Free tool
Board foot calculator
Board feet and cost, from thickness, width and length. Nothing is sent anywhere — the arithmetic happens in your browser and the page keeps working with the connection off.
How it works
A board foot is 144 cubic inches of timber — a piece one inch thick, twelve inches wide and twelve inches long, or anything else of the same volume. Hardwood is sold this way because you are buying material, not surface.
The formula, with every measurement in inches:
board feet = thickness × width × length ÷ 144
Length is usually quoted in feet, so the shortcut most people use is to divide by 12 instead and leave the length in feet:
board feet = thickness (in) × width (in) × length (ft) ÷ 12
A worked example
Six boards of 8/4 walnut, 7 inches wide and 10 feet long, at $12.50 per board foot.
Each board is 2 × 7 × 10 ÷ 12 = 11.67 board feet. Six of them is 70 board feet, and at $12.50 that is $875.
The mistake that costs money
Hardwood is priced on its nominal thickness. A 4/4 board is sold as one inch thick even after surfacing has taken it down to about 13/16. Use the thickness you are being charged for, not the one your calipers report, or your total will come out short of the invoice.
Questions
- What is a board foot?
- A board foot is a unit of volume used for hardwood: 144 cubic inches. That is a piece one inch thick, twelve inches wide and twelve inches long — or any other combination that multiplies to the same volume. It measures how much timber you are buying, which is why hardwood is priced by it and sheet goods are not.
- How do you calculate board feet?
- Multiply thickness in inches by width in inches by length in inches, then divide by 144. If your length is in feet, multiply thickness by width by length in feet and divide by 12 instead. Both give the same answer.
- Do I use the nominal or the actual thickness?
- Use the thickness you are being charged for, which for rough-sawn hardwood is the nominal one. Hardwood is quoted in quarters: 4/4 is one inch, 8/4 is two inches. A 4/4 board that has been surfaced measures about 13/16 of an inch, but it is still sold and priced as a full inch.
- Is a board foot the same as a square foot?
- No. A square foot is area and ignores thickness; a board foot is volume. Two boards of the same face size but different thicknesses cover the same square footage and cost different amounts.
- How do I work out board feet for plywood?
- You normally do not. Sheet goods — plywood, MDF, melamine — are sold by the sheet, not by the board foot. For those you want a cutting plan rather than a volume, which is what SawKit does.
- Should I add extra for waste?
- Yes, if you are buying rough stock. Allowing 15 to 30 per cent over your finished measurements is normal, more if the boards have significant defects or you need to match grain. This calculator gives you the exact figure; the allowance is a judgement about your material.
Cutting sheet goods instead?
Board feet are for timber. Plywood, MDF and melamine are sold by the sheet, and the question there is not how much volume you need but how to get your parts out of the sheets with the least waste.
For that, use theplywood cut calculator: enter your parts and the sheet, and it shows how many sheets you need, the waste and every cut, with the kerf counted. Or readhow to cut a sheet of plywood with the least waste, which covers the part no software does for you.