Cut list calculator: pieces per board and boards needed

New to this? Words explained.

Why kerf matters

Every cut turns a strip of wood into sawdust — about ⅛ in (3 mm) for most circular, miter and table saw blades, less for thin-kerf blades. It sounds trivial until the pieces divide the board exactly. Four 24 in pieces need 96 in plus three kerfs, and an 8 ft board is only 96 in. You get three — the full story is in How many 24 in pieces from an 8 ft board, and the framing version in How many 16 in pieces from an 8 ft 2x4.

pieces per board = (board length − trim + kerf) ÷ (piece + kerf), rounded down
boards needed = packed longest-first across boards

Bookcases and boxes: the width trap

When the shelves sit between the sides — the usual way a bookcase is built — they are shorter than the case is wide, by two side thicknesses. A 30 in wide case with ¾ in sides takes 28½ in shelves. Cut them 30 in and the case grows to 31½ in. Enter the outside width in the optional box above and the calculator works out the shelf length for you.

shelf length = outside width − 2 × side thickness
30 in − 2 × ¾ in = 28½ in

The full layout for that case is on Cut list for a 30 in wide bookcase: two 8 ft 1×12s give both sides and four shelves. Before you cut, check the shelves won’t bow under books with the shelf sag calculator.

How the layout is packed

The calculator first sorts the pieces longest first and places each one on the first board that still has room (“first-fit decreasing”). It then tries a second layout that fills each board as full as it will go, and keeps whichever needs fewer boards. The difference shows up on furniture lists: for the bookcase above, first-fit puts both 36 in sides on one board and needs three, while one side and two shelves per board needs only two. The table under the result lists each board’s cuts and the offcut left over, so you can mark the boards at the store or on the bench.

A piece exactly as long as the board needs no cut at all, so it fits even with a kerf set — that is how the long sides in Cut list for a 4×8 raised garden bed come out as whole 8 ft 2×6s. Set an end trim and they no longer fit, because the board is then shorter than the piece.

Rough-stock takeoff for hardwood

Hardwood dealers sell rough boards by the board foot in quarter-inch thicknesses, so a furniture cut list has to be turned into board feet before you order. Switch the first box to the takeoff and enter each part’s finished size. The calculator picks the thinnest rough thickness that still planes to the part, using the NHLA standard surfaced thicknesses, adds a working allowance, and totals the board feet by thickness.

Each part also gets 1/4 in extra width for jointing an edge and ripping, and 1 in extra length for squaring the ends. Those are working allowances, not a rule — long, wide or glued-up parts often need more. The waste percentage on top covers knots, checks and the parts you cut wrong. For single boards, the board foot calculator and the guide What is a board foot cover the arithmetic.

Tips for a better cut list

• Measure your real stock. “8 ft” boards are often a fraction over 96 in, and sometimes under. Factory ends can be split or out of square — add an end trim if you need to square them.
• Cut long parts first. Long pieces are the hardest to fit and need the straightest, clearest wood. Short parts can come from the offcuts.
• Plan for defects. Knots, checks and bowed sections mean a board rarely yields its theoretical count. Buy one extra board for every five or so.
• Mind the grain and colour. For furniture, parts that sit side by side look better cut from the same board.
• Crosscut after ripping if you also need narrower widths; ripping a long board is easier and safer than ripping short pieces.

This calculator handles lengths only. It does not lay out rectangles on a sheet of plywood; for sheet counts by area use the plywood calculator and sketch the parts on a scaled drawing of the sheet.

Trim work follows the same rules. The battens for Board and batten spacing for a 12 ft wall are one 8 ft stick each, but the top rail and any shorter pieces are worth running through the calculator so the offcuts get used.