Deck Calculator
Free deck calculator that turns your deck's length and width into decking boards, linear feet, fasteners, and an estimated material cost. Set board size and waste to plan a build and compare contractor quotes before you buy.
Estimate decking boards and cost
How the deck calculator works
Building a deck starts with the decking itself. This deck calculator treats the surface as an area and each board as a strip of coverage: multiply length by width for square feet, add a waste allowance, then divide by the area one board covers. A 16 ft by 12 ft deck is 192 square feet; with 10% waste and 16-foot 5/4x6 boards, that is roughly 28 boards and about 448 linear feet.
The tool also estimates deck screws — figure about 3.5 fasteners per square foot with joists 16 inches on center. Boards and linear feet are what the lumberyard needs; the square-foot cost gives you a number to check quotes against. For the framing beneath, the same footprint drives your joist, beam, and footing counts.
Stairs, railings, and stain
Once the deck surface is planned, three add-ons remain. Stairs: a deck stair calculator divides the total height from deck to grade by a 7 to 7-3/4 inch riser to get the step count, pairing each with a 10 to 11 inch tread. Railings: a deck railing spindle spacing calculator spreads balusters evenly so no gap lets a 4-inch sphere pass, the guard requirement in the residential code; a 36-inch guard height is standard.
Finish: a stain calculator deck divides the surface area — plus rails and stairs — by the coverage on the can, typically 200 to 300 square feet per gallon per coat on smooth wood and less on rough or thirsty boards. Composite decking skips stain entirely, which changes the long-run cost more than the up-front board price.
How to use this calculator
- Measure the deck footprint in feet. Measure the length and width of the deck surface in feet. For an L-shaped or wrapped deck, split it into rectangles, run each through this deck building calculator, and add the board counts together.
- Use the deck material calculator for boards. Enter your board face width and length so the deck material calculator divides the deck area by the coverage of one board. A standard 1/8-inch gap between boards is assumed, which is why a 5.5-inch board is treated as 5.625 inches wide.
- Add a deck cost calculator estimate. Enter your local material price per square foot and the tool works as a deck cost calculator, multiplying deck area by that rate. Pressure-treated pine sits at the low end and capped composite at the high end.
- Plan stairs and railing spacing. Use the result to size the rest of the build: a deck stair calculator counts treads from the total rise, and a deck railing spindle spacing calculator keeps the gap under 4 inches to meet the guard code.
Frequently asked questions
How does a deck building calculator estimate boards?
It divides the deck's square footage, plus a waste allowance, by the area one board covers — its length times its face width plus a 1/8-inch gap — then rounds up to whole boards and multiplies by board length for linear feet.
What is the code for deck railing spindle spacing?
Balusters must be spaced so a 4-inch sphere cannot pass between them, and residential guards are at least 36 inches tall. Distribute the spindles evenly so none of the gaps exceed that limit.
How do I size deck stairs?
Divide the total height from deck to ground by a riser between 7 and 7-3/4 inches to get the number of steps, and pair each riser with a tread of at least 10 inches. A stair takeoff automates this from the total drop.
How much stain does a deck need?
One gallon covers about 200 to 300 square feet per coat on smooth decking and less on rough or weathered wood. Include the rail and stair surfaces, and plan on two coats for new bare wood.
What does a deck cost in 2026?
In 2026, decking materials run about $8 to $35 per square foot — pressure-treated at the low end, capped composite at the high end — and installed prices are roughly double once labor is added. Enter your own rate for a local estimate.
Deck size vs boards and material cost
| Deck size | Area | 5/4x6 boards (16 ft) | Material @ $25/sq ft |
|---|---|---|---|
| 10 × 10 ft | 100 sq ft | ~15 boards | ~$2,500 |
| 12 × 16 ft | 192 sq ft | ~28 boards | ~$4,800 |
| 16 × 20 ft | 320 sq ft | ~47 boards | ~$8,000 |
| 20 × 24 ft | 480 sq ft | ~70 boards | ~$12,000 |
Board counts include 10% waste for a straight lay. Material rate covers decking, framing, and fasteners at a mid-range level; pressure-treated builds run lower and capped composite higher, and labor roughly doubles an installed price.