Lumber Calculator

By Uzair Arshad , Senior Civil and Structural Engineer

Last updated: April 27, 2026

This lumber calculator converts board dimensions into board feet so you can estimate quantity, waste, and cost before buying. Enter the number of boards, length, width, and thickness to get a purchase-ready total with optional pricing.

How to use this calculator

Enter how many boards you plan to buy or cut. Set the count to the number of identical boards. If you have mixed sizes, run this lumber calculator once per size and add the totals.
Enter the board length in feet. Use the "Additional inches" field if the board isn't an even number of feet. For example, a 6 ft 6 in board is 6 in the feet field and 6 in the inches field.
Enter width and thickness in inches. Use actual measured dimensions when accuracy matters, not the nominal label. A nominal 2x4 actually measures 1.5 in by 3.5 in. For rough-sawn hardwood sold by the board foot, use the actual rough thickness your supplier quotes.
Set the waste allowance. Keep 10% for general projects like shelving, decking, or trim. Raise it to 15% or 20% for furniture builds or when selecting for grain, color, or figure. Waste covers crosscuts, end checks, knots, and boards you reject at the yard.
Enter price per board foot (optional). Type your supplier's price per board foot to see an estimated material cost. Leave it at zero if you only need the board footage total.

Pro tip: Keep a short cut list next to this lumber calculator when estimating for furniture, shelving, or small shop projects. Calculate each board size as a separate run, then add all the waste-adjusted totals for your full purchase list. This approach prevents under-ordering when boards vary in width or thickness.

How the calculation works

Board feet:
Board feet per board = Length (ft) × Width (in) × Thickness (in) / 12

Totals:
Total board feet = Board feet per board × Number of boards
Waste-adjusted BF = Total board feet × (1 + Waste % / 100)

Cost:
Estimated cost = Waste-adjusted BF × Price per board foot

Length: Board length in feet (add extra inches if the board isn't an even number of feet)
Width: Board width in inches, measured across the face
Thickness: Board thickness in inches (use actual measured thickness for accuracy)
Waste %: Extra material for cuts, defects, knots, end checks, and grain selection (default 10%)
Price per BF: Supplier's price per board foot for cost estimation (optional)

A board foot is the standard unit for measuring and pricing lumber. This lumber calculator uses that unit to convert your board dimensions into a purchase-ready total. One board foot equals a piece of wood 12 inches long, 12 inches wide, and 1 inch thick, or 144 cubic inches of material.

Main formula:

Board feet = Length (ft) × Width (in) × Thickness (in) / 12

Variables:

Length = board length in feet. Add extra inches as a decimal (6 inches = 0.5 ft).
Width = board width in inches, measured across the face of the board.
Thickness = board thickness in inches. Common values are 0.75 (3/4 in), 1.0, 1.25 (5/4 in), 1.5, and 2.0.
12 = the divisor that converts the mixed-unit product (ft × in × in) into board feet.

Length is measured in feet while width and thickness use inches because that's how lumber yards label and sell stock. The formula divides by 12 to normalize the result into the board foot unit.

Example:

5 boards, each 8 ft long, 10 in wide, and 1.25 in thick, with 10% waste at $6.50 per board foot.

Step	Calculation
Board feet per board	8 × 10 × 1.25 / 12 = 8.33 BF
Total board feet	8.33 × 5 = 41.67 BF
Waste (10%)	41.67 × 0.10 = 4.17 BF
Waste-adjusted total	41.67 + 4.17 = 45.83 BF
Estimated cost	45.83 × $6.50 = $297.92

Actual vs. nominal dimensions:

Nominal lumber sizes (2x4, 2x6, 1x6) don't match actual dimensions. A nominal 2x4 measures 1.5 × 3.5 in. If you enter the nominal size, your board foot estimate will be higher than the real volume. Rough-sawn hardwood is typically sold at actual thickness (4/4 = ~1 in, 5/4 = ~1.25 in, 8/4 = ~2 in), so use the thickness your supplier quotes.

Waste factor:

Waste covers material lost to crosscuts, end checks, knots, warped boards, and grain selection. A 10% waste factor is standard for straightforward projects. Raise it to 15% or 20% when building furniture or selecting boards for color and figure. Buying the exact calculated amount often leaves you one board short after trimming defects.

Quick rule:

A 1 in thick board that is 12 in wide and 1 ft long = exactly 1 board foot
For rough pricing, hardwood typically runs $4 to $15 per board foot depending on species (2026 prices)
Mixed-width or mixed-thickness boards should be calculated in separate groups, then totaled
1,000 board feet = 1 MBF (the unit mills use for bulk pricing)

Assumptions and limitations:

This lumber calculator assumes rectangular boards with uniform dimensions. Irregular shapes, live-edge slabs, or tapered stock require manual measurement.
The calculator does not account for surfacing loss. Rough lumber planed to finished thickness will yield slightly less usable volume than the raw board foot total.
Cost estimates use a flat rate per board foot. Suppliers may price differently by species, grade, or quantity tier.
Dimensional lumber (2x4, 2x6, etc.) is often sold by the linear foot, not the board foot. Match the unit your supplier quotes to avoid confusion.

Frequently Asked Questions

How do I calculate board feet of lumber?

Multiply the board's length in feet by its width in inches by its thickness in inches, then divide by 12. For example, 5 boards that are 8 ft long, 10 in wide, and 1.25 in thick equal 41.67 board feet before waste. Add 10% for cuts and defects to get the purchase quantity.

How do you calculate a board foot of lumber?

A board foot equals length in feet times width in inches times thickness in inches, divided by 12. One 8 ft board that is 6 in wide and 1 in thick equals 4 board feet. Multiply by the number of boards for your total, then add a waste factor before ordering.

Should I use nominal or actual lumber dimensions?

Use actual measured dimensions for accurate board foot estimates. A nominal 2x4 measures 1.5 by 3.5 inches, so entering 2 by 4 overstates board feet by about 31%. Rough-sawn hardwood is sold at actual thickness (4/4 = ~1 in, 5/4 = ~1.25 in), so match the dimensions your supplier quotes.

How much lumber do I need?

You need enough lumber to cover the calculated board footage plus a safety margin. If the calculator shows 80 board feet and you apply 10% waste, plan for 88 board feet. Use the exact board dimensions for hardwood, trim, shelving, or similar stock to avoid over-ordering.

How to calculate BF of lumber?

BF stands for board feet. The formula is length times width times thickness divided by 12, with length in feet and width and thickness in inches. A 12 ft board that measures 2 in by 6 in actual yields 12 BF. Always use actual dimensions for accuracy.