Measure the footprint
Enter the overall finished length and width of your rectangular deck.
Free planning tool
Advanced Deck Material & Cost Calculator
Estimate deck boards, joists, fasteners, waste, and known material costs for a rectangular outdoor deck—in minutes.
✓ Imperial & metric✓ Private, local calculations✓ Print & PDF export
Start your estimate Rectangular deck estimator
Plan your deck materials
Start with the prefilled example or enter your own measurements. Prices are optional.
Your calculator inputs are processed and stored locally in your browser. They are not uploaded to an external server.
Your estimate will appear here
Review the defaults or enter your deck details, then select Calculate materials.
Planning guide
Build a more informed material estimate
Understand the quantities behind the result before ordering deck boards, framing lumber, and fasteners.
Match the products
Use the actual board width, stock length, gap, and joist-piece length.
Review allowances
Select waste and fastener allowances appropriate for your layout.
Confirm before buying
Take the printable list to a supplier or contractor for verification.
Getting started
Use DeckCalc with confidence
Everything runs locally, so you can plan without an account.
Choose a calculator
Use Quick Mode for one rectangle. Choose Advanced Mode for sections, levels, layouts, optional materials, labour, and customer estimates.
Save and reuse pricing
Advanced projects autosave after valid changes. Create price presets for products and labour you use regularly.
Export an estimate
Download JSON backups, CSV summaries, printable HTML, or locally generated branded PDFs. Exported files are never uploaded.
Install and work offline
When your browser offers Install app, use it for standalone access. After the first successful visit, cached calculator files remain available offline.
Protect local projects
Customer and pricing data stays in this browser. Regularly use Storage and Privacy to export a full backup because clearing site data removes local records.
Restore a backup
Open Storage and Privacy, choose Import full backup, validate the file, then merge it or explicitly replace local data.
Board planning
How deck-board quantities are calculated
The calculator first finds how many rows fit across the deck using actual board width plus the selected gap. It allows for no gap after the final row. Rows are multiplied by the board run length to get the total linear requirement, then divided by stock-board length. Both stock quantity and waste are rounded upward.
This linear approach works well for early planning but does not optimize cutting patterns, joints, picture-frame borders, or offcuts.
Product dimensions
Standard deck-board sizes
Common wood decking is sold under nominal labels such as 5/4×6 or 2×6, often in 8, 10, 12, 16, and 20-foot lengths. Composite and PVC products use manufacturer-specific profiles and lengths. Availability varies by market, species, color, and supplier.
Use the dimension printed in the current product specification, not an assumed standard.
Measure accurately
Nominal vs actual board width
A board sold as “2×6” is a nominal size; a finished wood board is commonly around 1.5 inches thick by 5.5 inches wide. The smaller actual width determines coverage, so using the nominal six-inch width can underestimate the rows required.
Installation spacing
Recommended gaps between deck boards
Common planning values range from 1/8 to 1/4 inch. Wood movement depends on moisture at installation and climate; manufactured decking can require different side and end gaps. Always follow current manufacturer instructions and account for drainage and ventilation.
Framing quantity
Common deck joist-spacing options
Twelve and sixteen inches on center are common planning selections; 24 inches may be permitted only in specific systems. Board direction, decking stiffness, loads, joist species, spans, and local rules affect the required spacing. This tool counts joist lines but does not determine structural suitability.
Purchase allowance
How much waste to add
Ten percent is a practical starting point for a straightforward rectangular deck. Five percent may be enough for highly efficient layouts with well-matched stock lengths. Diagonal patterns, many joints, defects, selective color matching, stairs, or picture framing can justify 15–20% or a project-specific takeoff.
Material comparison
Pressure-treated wood vs composite decking
Pressure-treated lumber often has a lower initial material price and can be cut with familiar woodworking tools, but it needs ongoing finishing and maintenance. Composite decking generally costs more upfront and requires system-specific fasteners and spacing, while offering consistent appearance and lower routine maintenance.
Transparent totals
How deck material costs are estimated
Costs are calculated only for prices you enter: final board quantity times price per board, estimated joist pieces times price per piece, and fastener boxes times price per box. Missing prices remain clearly marked and are excluded from the known subtotal. Labor, tax, delivery, permits, tools, finishes, railings, beams, posts, and footings are not included.
Straight answers
Frequently asked questions
Practical context for interpreting your deck material estimate.
01How many deck boards do I need?+
Divide the dimension across the boards by the combined actual board width and gap, then multiply the resulting rows by the board run length. This calculator converts that linear total into purchasable boards and adds your selected waste allowance.
02How do I calculate deck square footage?+
For a rectangular deck, multiply the deck length by the deck width. A 20-foot by 12-foot deck has 240 square feet of surface area.
03What is the actual width of a 2x6 deck board?+
A surfaced 2×6 wood deck board is commonly about 5.5 inches wide, but dimensions vary by product, moisture content, and manufacturer. Measure or verify the actual product specification.
04How much space should be left between deck boards?+
Common planning gaps include 1/8, 3/16, and 1/4 inch. The right gap depends on material, moisture, climate, and manufacturer instructions. Always follow the product's installation guidance.
05How much extra decking should I purchase for waste?+
Ten percent is a common starting allowance for a simple rectangular layout. Complex cuts, diagonal layouts, defects, and selective board matching can require 15–20% or more.
06How far apart should deck joists be?+
Common planning options are 12, 16, or 24 inches on center. The permitted spacing depends on decking, joist species and grade, loading, spans, installation angle, and local code. This calculator estimates quantity only.
07How many screws are needed per deck board?+
Face-fastened wood decking commonly uses two fasteners at each board-and-joist intersection. Hidden fastening systems and manufacturer-specific details can differ.
08Can this calculator be used for composite decking?+
Yes. Select composite decking and enter the product's actual width, available length, required gap, and recommended joist spacing. Confirm all settings with the manufacturer.
09Does this calculator calculate cutting patterns?+
No. Board quantity is an approximate linear-length calculation. It does not optimize staggered joints, offcut reuse, picture framing, breaker boards, or a cutting layout.
10Does this calculator verify local building codes?+
No. It does not approve structural design or verify joist spans, beams, footings, loads, connections, permits, or local codes. Consult qualified local professionals before construction.