Deck Calculator
Estimate deck area, board quantities, waste allowance and material cost.
Enter your deck dimensions and board details below to estimate how much decking material you may need.
Your Deck Estimate
Enter your deck measurements above to estimate your decking materials.
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About the Creator
MyCruncher — Founded by Bobby Dues
MyCruncher provides free online calculators designed to make everyday calculations easier to understand and use.
Meet Bobby Dues →Free Deck Calculator – Estimate Decking Boards, Square Footage and Material Cost
Planning to build a new deck or replace existing decking? The free MyCruncher Deck Calculator helps estimate your deck's square footage, the number of decking boards needed, waste allowance, total board length, and material cost.
Whether you're planning a backyard deck, replacing worn deck boards, comparing lumber prices, or preparing a home improvement budget, knowing the estimated materials can help you plan your project.
Enter your deck dimensions, decking board size, board spacing, waste allowance, and board price to generate a material estimate.
The calculator focuses on surface decking materials rather than the complete structural design or total installed cost of a deck.
How to Use the Deck Calculator
The MyCruncher Deck Calculator uses seven inputs to estimate decking board quantities and material costs.
- Enter your deck length. Provide the overall deck length in feet, such as 12, 16, or 20 feet.
- Enter your deck width. Provide the deck width in feet. Together with the length, this determines the rectangular deck area.
- Select your board width. Choose the actual width of the decking material, such as 5.5 inches.
- Choose your board gap. Select the intended spacing between adjacent boards, following the decking manufacturer's installation requirements.
- Select the board length. Choose the stock length of the decking boards you plan to purchase, such as 12 feet.
- Choose a waste allowance. Add an allowance for trimming, cutting, material defects, and other expected waste.
- Enter the price per deck board. Provide the price of one board in dollars. Use a current price for the material and length you selected.
- Click Calculate Deck Materials. The calculator generates your estimated decking material quantities.
- Review your deck estimate. Examine total deck area, estimated deck boards, boards with waste, total board length, and estimated decking cost.
You can change the dimensions, board size, spacing, waste allowance, or price to compare different material scenarios.
Use Reset when you want to return to the calculator's initial settings.
How Do You Calculate Deck Square Footage?
For a rectangular deck, multiply the length by the width to determine the surface area in square feet.
Both dimensions should be measured in feet.
For example, a deck that measures 16 feet long and 12 feet wide has an area of 192 square feet.
Deck square footage provides a useful starting point for estimating the amount of surface decking required.
Board quantities also depend on the width of the boards, spacing between boards, the direction they run, cutting requirements, and stock lengths.
Deck Square Footage Chart
The following table shows the surface area of several common rectangular deck sizes.
| Deck Size | Square Footage |
|---|---|
| 8 ft × 10 ft | 80 sq ft |
| 10 ft × 12 ft | 120 sq ft |
| 12 ft × 12 ft | 144 sq ft |
| 12 ft × 16 ft | 192 sq ft |
| 14 ft × 20 ft | 280 sq ft |
| 16 ft × 20 ft | 320 sq ft |
| 20 ft × 20 ft | 400 sq ft |
These values represent surface area only. The amount of decking required may vary with layout and material dimensions.
How Many Decking Boards Do I Need?
The number of boards needed depends on the deck dimensions and the actual size of the decking material.
Board spacing and installation direction also affect the estimated quantity.
For a simple straight-board layout, an approximate board coverage width can be estimated by adding the board width and the planned gap.
For example, a 5.5-inch-wide board with a 3/16-inch gap has an approximate repeating coverage width of 5.6875 inches.
The required number of board rows can then be estimated by dividing the deck dimension across those rows by the approximate coverage width and rounding up.
The last row may require trimming, and the actual number of purchased stock boards depends on how many pieces are needed to complete each row.
For more complicated patterns, a detailed cutting layout is necessary.
Deck Material Calculation Example
Example: Suppose you're planning a rectangular backyard deck that measures 16 feet long by 12 feet wide.
You plan to use decking boards that are 5.5 inches wide and 12 feet long, with a 3/16-inch gap between adjacent boards.
For this illustration, the 12-foot boards run across the deck's 12-foot dimension, creating rows across the 16-foot dimension.
Example Deck Information
- Deck Length: 16 ft
- Deck Width: 12 ft
- Board Width: 5.5 inches
- Board Gap: 3/16 inch
- Board Length: 12 ft
- Waste Allowance: 10%
- Price Per Board: $18
Step 1: Calculate Deck Area
Multiply the deck length by the width.
The total rectangular deck surface is 192 square feet.
Step 2: Convert the 16-Foot Dimension Into Inches
Multiply 16 feet by 12 inches per foot.
Step 3: Calculate Approximate Board Coverage Width
Add the board width and spacing allowance.
Step 4: Estimate Board Rows
Divide the 192-inch dimension by the approximate board coverage width.
Round up to allow sufficient coverage.
For this example layout, each row uses one 12-foot board running across the 12-foot span.
The final row can be trimmed to fit the finished deck width.
Step 5: Add a 10% Waste Allowance
Multiply the estimated 34 boards by 1.10.
Because boards are purchased as whole units, round up.
Step 6: Calculate Board Length
Multiply the purchase quantity by the stock length.
The example order contains 456 linear feet of 12-foot decking boards.
Before the waste allowance, 34 boards represent 408 linear feet.
Step 7: Calculate Estimated Decking Cost
Multiply the number of boards being purchased by the price per board.
The estimated purchase cost for these decking boards is $684, before sales tax, delivery, fasteners, and other project expenses.
Deck Calculation Example Summary
| Calculation | Illustrative Result |
|---|---|
| Deck Area | 192 sq ft |
| Board Width | 5.5 inches |
| Board Length | 12 ft |
| Board Gap | 3/16 inch |
| Estimated Board Rows | 34 |
| Waste Allowance | 10% |
| Boards Including Waste | 38 |
| Linear Feet Purchased | 456 ft |
| Board Material Cost | $684 |
This example demonstrates how deck dimensions, board spacing, material lengths, and waste can be combined for a preliminary material estimate.
This is one illustrative straight-board layout, not a guarantee of the live calculator's exact board-count algorithm. Actual quantities may differ due to board direction, butt joints, cutting layouts, gaps, perimeter details, and rounding. Always verify a physical cut plan before ordering.
How Much Extra Decking Should You Allow for Waste?
A waste allowance provides additional material for cutting, trimming, damaged boards, irregular areas, and other installation requirements.
Ten percent is one commonly used preliminary allowance for relatively simple decking layouts.
However, the actual amount of waste depends on the project.
Deck Board Waste Comparison
The following chart starts with 34 boards before waste and assumes a price of $18 per board.
| Waste | Boards to Buy | Board Cost |
|---|---|---|
| 0% | 34 | $612 |
| 5% | 36 | $648 |
| 10% | 38 | $684 |
| 15% | 40 | $720 |
| 20% | 41 | $738 |
The board counts are rounded up to whole boards.
More complicated layouts, angled patterns, picture-frame borders, and numerous cutouts may require a greater allowance.
The waste percentage is a planning input, not a substitute for a detailed material takeoff.
How Does Deck Board Spacing Affect Material Quantities?
Deck boards usually require an appropriate gap between adjacent pieces.
Gaps can help accommodate drainage, ventilation, and changes in material dimensions caused by moisture or temperature.
The correct spacing depends on the decking product and installation conditions.
Common Deck Gap Measurements
| Fractional Gap | Decimal Inches |
|---|---|
| 1/8 inch | 0.125 |
| 3/16 inch | 0.1875 |
| 1/4 inch | 0.25 |
These are common fractional measurements used when discussing deck board spacing, not universal installation recommendations.
A wider gap changes the overall coverage of a row of boards and may change the estimated quantity needed.
Pressure-treated lumber, hardwood, composite, and PVC decking can have different spacing requirements.
Always follow the installation guide for the exact decking product, including side gaps, end gaps, temperature requirements, and fastening instructions.
Why Does Actual Board Width Matter?
Some decking materials are sold using nominal size descriptions that differ from their actual measured dimensions.
For example, a common nominal 5/4×6 wood decking board may have an actual width of approximately 5.5 inches.
Composite and other manufactured decking products may have different actual widths.
Using an incorrect board width can affect the estimated number of board rows needed to cover your deck.
Measure the actual board or consult the product specification before selecting its width in the calculator.
How Does Board Length Affect a Deck Estimate?
The length of the boards you purchase can affect material usage, butt joints, waste, and installation planning.
For example, a deck layout using 12-foot boards may require more end-to-end joints if the boards run across a 16-foot span.
Choosing longer boards may reduce the number of joints in some designs, depending on available stock lengths.
However, longer boards can have different prices, handling requirements, and installation considerations.
Choosing a Board Length
Before ordering materials, consider how the boards will run relative to the deck dimensions and supporting joists.
A detailed layout should account for joint placement, adequate support, perimeter cuts, and any manufacturer-required fastening details.
The most economical stock board length depends on your cutting plan and available pricing.
Wood Decking vs. Composite Decking
Decking materials vary in appearance, maintenance needs, product specifications, and cost.
Two commonly considered options are wood and composite decking.
Wood Decking
Wood decking may include pressure-treated lumber, cedar, redwood, or other suitable wood products.
The appearance, durability, maintenance requirements, and price vary by species, grade, treatment, and local conditions.
Many wood decks require periodic cleaning and protective maintenance.
Composite Decking
Composite decking is manufactured from materials designed for exterior decking applications.
Different product lines can have different finishes, dimensions, installation requirements, and warranty conditions.
Composite products may require less routine finishing than some natural wood products, but they still need appropriate care and installation.
Material Comparison
| Consideration | Wood | Composite |
|---|---|---|
| Appearance | Natural Wood | Manufactured Finishes |
| Maintenance | Varies by Wood | Varies by Product |
| Board Sizes | Product-Specific | Product-Specific |
| Spacing | Follow Specifications | Follow Manufacturer |
| Cost | Compare Quotes | Compare Quotes |
The MyCruncher Deck Calculator can help compare board quantities and board-only costs using the selected dimensions and prices.
It does not independently evaluate structural suitability, long-term durability, or maintenance expenses.
How Much Do Decking Boards Cost?
Decking board prices depend on material type, board dimensions, grade, manufacturer, retailer, and location.
The calculator lets you enter the price per board rather than using a fixed market price.
To estimate the board-only purchase cost, multiply the estimated purchase quantity by the current price per board.
Decking Price Comparison Example
The following table assumes a purchase quantity of 38 boards.
| Price Per Board | Estimated Cost |
|---|---|
| $15 | $570 |
| $18 | $684 |
| $22 | $836 |
| $25 | $950 |
| $30 | $1,140 |
These are mathematical price scenarios rather than current retail quotations.
The quantity and overall cost may change when the decking product or layout changes.
What Is the Difference Between Square Feet and Linear Feet?
Square feet measure area, while linear feet measure length.
Square Feet
Square footage describes the deck surface area.
Linear Feet
Linear footage describes the combined length of material.
For example, 38 boards that are each 12 feet long represent:
These are different measurements and should not be used interchangeably.
Square footage helps describe the area being covered, while linear footage helps describe the amount of decking material.
How to Estimate Deck Materials for an Irregular Shape
Decks with L-shaped layouts, angled sections, or other irregular dimensions may be more difficult to estimate using one rectangular measurement.
One preliminary approach is to divide the deck into smaller rectangular sections.
Calculate the area of each section, then add the areas together.
L-Shaped Deck Area Example
Suppose an L-shaped deck can be represented by two nonoverlapping rectangular areas.
Section 1 measures 12 feet by 10 feet.
Section 2 measures 8 feet by 6 feet.
Add the sections together.
The combined area is 168 square feet.
However, board quantities for irregular decks also depend on the cutting layout, board orientation, joints, and waste.
The basic Deck Calculator is best treated as a preliminary estimator for simple dimensions, not a complete cutting diagram for irregular designs.
Does Deck Board Direction Affect the Estimate?
Yes. The direction decking boards run can significantly affect the number of purchased boards, the location of joints, and cutting waste.
For example, 12-foot boards may fit one dimension of a 12-by-16-foot deck without an end joint.
If those same boards instead run along the 16-foot direction, each row requires a plan for additional material and properly supported joints.
Diagonal or decorative patterns can add even more cutting requirements.
The simple material example in this guide assumes a specific straight-board orientation. Actual results should be confirmed using your intended layout.
What Materials Are Not Included in the Deck Calculator?
The MyCruncher Deck Calculator focuses on estimating surface decking boards and their material cost.
A complete deck project may require many additional materials and expenses.
- Joists. Framing members that support the decking boards.
- Beams. Structural members that support joists or transfer loads to posts.
- Posts and footings. Structural supports and foundations designed for applicable loads and site conditions.
- Ledger and connectors. Components used in certain deck attachment and framing designs.
- Fasteners. Suitable screws, clips, brackets, hangers, and other hardware.
- Railings and guards. Safety components where required.
- Stairs and landings. Additional framing, decking, treads, railings, and related materials.
- Fascia and trim. Perimeter finishing materials.
- Labor. Costs for layout, construction, installation, and cleanup.
- Permits and inspections. Applicable building department requirements.
- Delivery and taxes. Additional purchase and transportation costs.
- Site preparation. Excavation, removal, grading, or other project-specific work.
These costs should be considered separately when preparing a full deck construction budget.
Why Are Joist Spacing and Structural Design Important?
Joists and other structural framing members support the weight of the decking, occupants, furniture, and applicable environmental loads.
Proper framing depends on the selected materials, spans, connections, load requirements, and local building codes.
Some decking products have specific allowable joist spacing requirements, which may also depend on board orientation.
The Deck Calculator does not design the framing, verify structural spans, determine foundation requirements, or establish building-code compliance.
Before building or modifying a deck, consult the applicable building department, product installation instructions, and qualified professionals when needed.
Does Building a Deck Require a Permit?
Deck permit requirements vary by jurisdiction, construction type, height, size, location, and structural details.
Some projects may require construction permits, inspections, engineering, or other approvals.
Replacing surface boards may involve different requirements from building a new structural deck.
Contact your local building department before beginning work to determine which requirements apply.
Helpful Tips for Planning a Deck Project
- Measure carefully. Confirm the finished deck dimensions before ordering materials.
- Choose the decking material early. Board dimensions, price, fastening, and spacing requirements can vary.
- Check actual board width. Do not assume nominal sizes equal finished dimensions.
- Plan board direction. Consider the relationship between decking runs and structural framing.
- Review board lengths. Select stock sizes with your cutting layout in mind.
- Allow for waste. Include additional boards for trimming, defects, and planned cuts.
- Verify manufacturer instructions. Follow product-specific gap, fastening, and support requirements.
- Compare material prices. Review current quotes from suppliers before finalizing a budget.
- Include structural materials. Surface boards are only part of the complete project.
- Check local permits. Confirm building and inspection requirements before construction.
- Plan a contingency. Unexpected site conditions and material needs can change total cost.
Frequently Asked Questions
How do I calculate deck square footage?
For a rectangular deck, multiply the length by the width in feet.
For example, a 16-by-12-foot deck has 192 square feet of surface area.
How many square feet is a 12-by-16 deck?
A 12-foot by 16-foot rectangular deck has 192 square feet of surface area.
How many decking boards do I need for a 12-by-16 deck?
The required number depends on board width, length, gaps, orientation, and waste.
In the straight-board example in this guide, 34 board rows are estimated before waste, with approximately 38 full 12-foot boards purchased after adding 10% waste.
Different layouts or cutting plans can produce different quantities.
Does board spacing change the number of boards?
Yes. The planned gap affects the width covered by each board row.
Different gaps may change the estimated quantity needed.
What size gap should I leave between deck boards?
Follow the installation instructions for your specific decking material.
Appropriate spacing can vary with product type, moisture content, installation temperature, and manufacturer requirements.
Is a 3/16-inch deck board gap acceptable?
A 3/16-inch gap is used in some decking installation systems.
However, it is not universally correct for every wood, composite, or PVC product. Verify the product's required gap before installation.
What is the actual width of a 5/4×6 deck board?
Many common nominal 5/4×6 wood decking boards measure approximately 5.5 inches wide.
Check the actual dimensions of the product being purchased.
How much decking waste should I add?
A 10% allowance can provide a preliminary starting point for a simple deck.
Complicated layouts, angled cuts, or numerous obstacles may require more material.
How much does it cost to buy deck boards?
Multiply the number of boards being purchased by the price per board.
For example, 38 boards at $18 each cost $684 before additional expenses.
Does the calculator include labor?
No. The Deck Calculator estimates the cost of the surface decking boards using your entered board price.
Labor and other project costs must be considered separately.
Does the calculator include deck framing?
No. Joists, beams, posts, footings, and structural connectors are not separately estimated by the surface decking calculator.
Does the calculator include deck screws?
The basic decking estimate does not separately calculate fastener quantities or costs.
Use your decking manufacturer's fastening specifications when planning hardware.
Can I calculate composite decking materials?
Yes, for preliminary surface board estimates using appropriate board dimensions, spacing, stock length, and price.
Confirm the actual product specifications and installation requirements before purchasing.
Can I calculate pressure-treated wood decking?
Yes. Enter the dimensions and current price for the boards you plan to use.
Account for the product's installation spacing, condition, and cutting requirements.
Do longer deck boards reduce waste?
Sometimes. Longer stock boards may reduce joints or offcuts for certain layouts, but the result depends on the overall cutting plan.
Compare different stock lengths before ordering.
What are linear feet of decking?
Linear footage is the combined length of the decking boards.
For example, 38 boards that are each 12 feet long represent 456 linear feet.
Is deck square footage the same as linear footage?
No. Square footage measures area, while linear footage measures length.
Both can be useful for planning decking materials.
Can I use the calculator for an L-shaped deck?
You can estimate separate rectangular areas, but the actual board quantity requires consideration of the cutting pattern and layout.
A detailed material takeoff is recommended for irregular shapes.
Can I use it for diagonal decking?
The basic estimate may provide an approximate planning reference, but diagonal layouts have different cutting and support requirements.
Verify quantities using the intended installation pattern.
Why does my material estimate differ from a contractor's estimate?
Differences may arise from board orientation, actual stock dimensions, joint placement, waste factors, product specifications, and other project details.
A contractor's estimate may also include materials and labor beyond the surface decking.
Does the calculator include railings or stairs?
No. Railings, stairs, structural components, and related materials should be estimated separately.
Does the calculator estimate the entire cost of building a deck?
No. It focuses on the surface decking boards and their estimated purchase cost.
A complete project budget must account for structural materials, hardware, labor, permits, and other expenses.
Can I use this calculator to replace old deck boards?
Yes. It can provide a preliminary estimate for replacement decking quantities.
Before replacement, inspect the existing framing and confirm that it is structurally suitable for continued use.
Do I need a permit to build a deck?
Permit requirements depend on local rules and project details.
Contact your local building department before starting construction.
Does the calculator verify building-code compliance?
No. It estimates surface material quantities and costs, not structural safety or compliance with building codes.
Are the deck material estimates guaranteed?
No. Actual quantities and costs vary with measurements, products, installation patterns, cutting plans, waste, and other conditions.
Is the MyCruncher Deck Calculator free?
Yes! The MyCruncher Deck Calculator is free to use for estimating deck area, decking board quantities, waste, linear footage, and board material cost.
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Important: The MyCruncher Deck Calculator provides preliminary educational material and cost estimates. Actual decking requirements can vary due to board dimensions, gaps, cutting layouts, waste, manufacturer instructions, and site conditions. The calculator does not provide structural engineering, framing design, building-code verification, or permit approval. Before purchasing materials or beginning construction, confirm the measurements, specifications, required support, fasteners, and local building requirements. Seek qualified professional advice when appropriate.