Lumber Calculator

How Does the Formula Work?

The lumber calculator works out how much wood a cut list adds up to. In the United States lumber is measured in board feet: one board foot is a piece 1 inch thick, 12 inches wide and 12 inches long, or 144 cubic inches. Enter the actual thickness and width of the boards (not the nominal size), the length of one piece, how many pieces you need and a waste percentage. The calculator returns the board feet of one piece, the piece count with waste, the total board feet, the total volume in cubic metres and the total length to order.

Nominal vs Actual Lumber Sizes

In the US, lumber is sold by nominal dimensions that differ from the minimum dressed sizes set out in Table 3 of the American Softwood Lumber Standard (Voluntary Product Standard PS 20, U.S. Department of Commerce). A 2×4 actually measures 1.5 × 3.5 inches (38 × 89 mm). A 2×6 is 1.5 × 5.5 inches. A 2×8 is 1.5 × 7.25 inches. A 2×10 is 1.5 × 9.25 inches. A 2×12 is 1.5 × 11.25 inches. A 4×4 post is actually 3.5 × 3.5 inches. A dressed size is the size once the rough-sawn board has been surfaced, so enter the size you actually have: the default values are the actual size of a 2×4, 1.5 × 3.5 inches.

Common Lumber Sizes and Board Feet

A 2×4×8 (actual 1.5 × 3.5 × 8 ft) contains 3.5 board feet. A 2×6×8 contains 5.5 BF. A 2×6×12 contains 8.25 BF. A 1×6×8 (actual 0.75 × 5.5 × 8) contains 2.75 BF. Ten 2×4×8s are 35 board feet, and with 10 percent waste the calculator rounds the order up to 11 pieces, 38.5 board feet.

Waste

The waste field adds a percentage to the piece count before it is rounded up to a whole piece: 100 pieces with 10 percent waste come to 110 pieces, and 7 pieces with 15 percent come to 9, because 8.05 pieces still means buying a ninth board. Choose the percentage from your own cutting list; straight framing cuts lose less than angled work or joinery.

Lumber Grades

Softwood lumber (used for framing) is graded under the American Softwood Lumber Standard (PS 20). The American Lumber Standard Committee does not grade boards itself: it maintains the standard, certifies the grading rules, approves design values and accredits the agencies whose inspectors grade and stamp lumber, while a separate consensus body, the National Grading Rule Committee, maintains the grade descriptions for dimension lumber.

Moisture Marks

PS 20 sets the seasoning marks: S-GRN for lumber surfaced green, S-DRY for lumber surfaced dry, and KD for lumber kiln dried to a maximum moisture content of 19 percent. Tighter limits come from the grading rules rather than from PS 20 itself, so for interior trim and furniture look for an MC 15 or KD 15 stamp, which means 15 percent or less.

Metric Sizes

Switch to Metric to enter thickness and width in centimetres and length in metres. The result then gives the volume of one piece in cubic centimetres with its board-foot equivalent beside it: a 5 × 10 cm piece 3 m long is 15,000 cm³, or 6.36 board feet.