Carpentry & Lumber Calculators
Turn deck, fence, and stair dimensions into a lumber list, and price rough lumber by the board foot.
Quick answer: board feet = thickness (in) × width (in) × length (ft) ÷ 12. Stairs: number of risers = total rise ÷ 7.75 in (IRC maximum), rounded up. Fence posts = fence length ÷ post spacing + 1, plus extra posts at gates and corners.
Decks, fences & framing
Deck Calculator
Decking boards and linear feet, joist count, deck screws or clips, and rough footings for a deck.
Open calculator →Deck Footing Calculator
Deck footing count, load per footing, minimum footing size for your soil, concrete bags, and sonotubes.
Open calculator →Fence Calculator
Fence posts, rails, pickets, and post concrete bags for picket, privacy, and board-on-board fences.
Open calculator →Fence Cost Calculator
Installed fence cost by material: material and labor per foot, gates, tear-out, permit, and cost per foot.
Open calculator →Stair Calculator
Risers, riser height, treads, total run, stringer length, and angle from total rise, with IRC checks.
Open calculator →Board Foot Calculator
Board feet, linear feet, and cost for lumber using thickness × width × length ÷ 12.
Open calculator →Building a cut list you can order from
Carpentry estimates are counts, not volumes: how many boards, posts, joists, pickets, and stringers. The safest approach is to calculate the count, round each line item up to whole pieces in the lengths your lumberyard stocks, and add a few spares for crooked or split boards.
Code minimums that affect quantities
Residential stairs under the International Residential Code allow a maximum riser of 7¾ in and a minimum tread of 10 in, so the total rise sets the riser count. Deck joist spans and footing sizes depend on lumber species, grade, and load. Use the IRC span tables (Section R507) or your local code rather than rules of thumb.
Board feet in common lumber sizes (nominal)
| Nominal size | Board feet per linear foot | Board feet in a 12 ft piece |
|---|---|---|
| 1 × 6 | 0.50 | 6 |
| 2 × 4 | 0.667 | 8 |
| 2 × 6 | 1.00 | 12 |
| 2 × 8 | 1.333 | 16 |
| 2 × 10 | 1.667 | 20 |
| 4 × 4 | 1.333 | 16 |
Frequently asked questions
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in feet, then divide by 12. A 2 × 6 that is 10 ft long is 2 × 6 × 10 ÷ 12 = 10 board feet.
How many stairs do I need for a 9 ft rise?
A 108 in total rise divided by the 7.75 in maximum riser is 13.9, so you need 14 risers of about 7.71 in each and 13 treads.
How many fence posts do I need?
Divide the fence length by the post spacing and add one. A 100 ft run with 8 ft spacing needs 100 ÷ 8 = 12.5, rounded up to 13 sections, so 14 posts, plus extra posts for gates and corners.