Common Lumber Sizes Explained (Nominal vs Actual + Cut Lists)

Ask for a 2x4 and you will not get a board that measures two by four inches. Nominal sizes are names. Actual sizes are what the tape reads. Cut lists that use the wrong one produce face frames that do not meet and tenons that hang in air.

This guide covers softwood nominal vs actual tables, hardwood S4S thickness language, common trim lengths, and why available stock length is a first-class input for linear cut optimization.

Linear optimization packs cut lengths onto stock sticks with kerf between cuts. If every rail is 900 mm and stock is 2400 mm, you get two rails per stick plus a usable or scrap remnant depending on kerf. If stock is 2100 mm, you may get only two with a tiny scrap — or one rail and a large remnant if grain defects force shorter usable length.

Worked example: 20 face-frame stiles at 720 mm and 20 rails at 450 mm, kerf 3 mm, stock 2438 mm (8 ft).

Use actual cross-section for joinery dimensions. Use nominal language on purchase notes when that is how you order (twenty 2x4x8). For hardwood, list finished or rough part length, target thickness after milling, and estimate BF separately for the purchase order.

Keep sheet goods on a separate material group — plywood sizes are not lumber sizes. See the plywood sheet sizes guide for 4x8, 5x5, and metric panels.

In metric markets, CLS and carcassing timber is sold as 38 x 89 mm, 45 x 95 mm, and similar — already stated as actual or finished sizes rather than 2x4 names. Put the millimetre size on the cut list and stock length in mm. Linear optimization works the same: parts, kerf, stock lengths.

Measure actual stock, write actual sizes into part rows, set real stock lengths, then run the free linear optimizer before you buy. For mixed cabinet jobs, nest plywood separately and optimize lumber as its own 1D list.