Lumber Calculator
Use this lumber calculator to count the studs or joists for a wall or floor and total the board feet. Enter the length, spacing on center, stock length and size, plus waste and a price per piece, or switch to find how many boards you need for a board-feet total.
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Studs or joists
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Plate pieces
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Pieces before waste
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Pieces to buy (with waste)
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Total board feet (actual size)
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Estimated cost
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Studs or joists = length ÷ spacing, rounded up, plus 1. Plate pieces = plate rows × length ÷ stock length, rounded up. Waste is added to the total and rounded up. Board feet use the actual size of the lumber (a 2×4 is 1.5 × 3.5 in). Corners, openings, blocking and cripples are not counted separately, so add them by hand or through the waste percentage.
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How it works
- How many studs do I need for a wall?
- Divide the wall length by the spacing, round up, and add 1. A 20 ft wall at 16 in on center is 240 ÷ 16 = 15, plus 1 = 16 studs. Corners, door and window openings and blocking need extra studs, so this is a starting count.
- How many plates does a wall need?
- A common layout is one bottom plate and two top plates, which is 3 rows. For a 20 ft wall that is 60 ft of plate, and with 8 ft stock pieces it is 60 ÷ 8 = 7.5, rounded up to 8 pieces. Set the plate rows to match your plan.
- What does on center spacing mean?
- On center (o.c.) is the distance from the middle of one stud or joist to the middle of the next. 12, 16 and 24 in are commonly used spacings. Closer spacing means more pieces, so the count and the cost go up. Check your plans or local code for the spacing you must use.
- How is waste calculated?
- The waste percentage is added to the total piece count and the result is rounded up. For example 24 pieces with 10% waste is 24 × 1.10 = 26.4, rounded up to 27. The percentage is your choice, so raise it for complex layouts or lower it for simple ones.
- How do I find the number of boards for a board-feet total?
- Switch the mode to boards for a board-feet total. Board feet per board = thickness × width × length in feet ÷ 12, using the actual size. A 2×6 that is 8 ft long is 1.5 × 5.5 × 8 ÷ 12 = 5.5 board feet. For 100 board feet plus 10% waste, 110 ÷ 5.5 = 20 boards.