# The Carpentry Calculator

> Free calculators for decks, stairs and wall framing, with to-scale drawings and a list of what to buy. US units. Stair results follow the International Residential Code (IRC): risers 7 3/4 in max, treads 10 in min.

Lengths can be typed the way people measure: 9' 2", 110, 36 1/2. Answers are rounded to the nearest 1/16 inch.

## Calculators

- [Deck calculator](https://thecarpentrycalculator.com/deck-calculator/): Deck boards, joists, screws and hangers to buy
- [Deck stair calculator](https://thecarpentrycalculator.com/deck-stair-calculator/): Steps, stringers and tread boards from the deck height
- [Stair calculator](https://thecarpentrycalculator.com/stair-calculator/): Risers, treads, stringers and framing square settings to code
- [Lumber calculator](https://thecarpentrycalculator.com/lumber-calculator/): Studs, plates and board feet for a wall
- [Board foot calculator](https://thecarpentrycalculator.com/board-foot-calculator/): Board feet and cost for a stack of boards

## Formulas

- Board feet = thickness (in) × width (in) × length (ft) ÷ 12, per board.
- Stairs: risers = total rise ÷ max riser (7 3/4 in), rounded up; riser height = total rise ÷ risers; treads = risers − 1; total run = treads × tread depth (10 in min). Stringer length = √(rise² + (run + one tread)²). Handrail required at 4 or more risers (IRC R311.7.8).
- Deck stairs: same riser math; tread = two 5 1/2 in boards with a 1/4 in gap = 11 1/4 in; stringers no more than 16 in apart, at least 2.
- Deck: rows of boards = deck width ÷ (board width + gap), rounded up; joists = length ÷ joist spacing, rounded up, + 1 (both end joists); deck screws = 2 per row of boards at every joist.
- Wall framing: studs = wall length ÷ spacing, rounded up, + 1, + 2 per corner, + 2 per opening; stud length = wall height − 4 1/2 in (one bottom and two top plates); plate stock = 3 × wall length. Precut studs: 92 5/8 in (8 ft wall), 104 5/8 in (9 ft), 116 5/8 in (10 ft).

## Notes

- Results are estimates for planning. Local codes can differ from the IRC; joists, beams and headers must be sized for the span and load.
- Lumber is priced and sold by nominal size (a 2x4 is 1 1/2 x 3 1/2 in actual) and in even foot lengths.