CategoriesCarpentry

Carpentry Calculators

Carpentry calculators for stairs, decks, and framing projects. Calculate dimensions, materials, and costs with building code compliance checks.

7 Calculators

Code compliant

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Framing and trim estimates are counts on a spacing, plus the waste from cuts.

Almost every carpentry quantity comes from a length divided by a spacing, plus one. Studs at 16 inch centres, joists at 16 or 24, deck boards at their actual width plus a gap. The plus one matters: a 12 foot wall at 16 inch centres needs 10 studs, not 9, before you add the extra ones at corners and either side of every opening.

Lumber is then bought in stock lengths, which is where the real waste appears. Framing a 9 foot wall from 10 foot studs wastes a foot per piece, while 16 foot boards on a 15 foot deck waste one. Picking the stock length that matches your dimensions saves more than shaving the spacing does.

Settle this before you calculate

Spacing and span: 16 inch centres is the default, 24 is allowed in some assemblies. Span tables decide joist depth, and depth decides price.
Stock lengths available: Lumber comes in 8, 10, 12, 14 and 16 foot pieces. Match your run to one of those and the waste drops sharply.
Openings and their extras: Every door and window needs king studs, jack studs and a header. Those pieces are why a stud count from spacing alone always reads low.

Where the estimate goes wrong

Forgetting the extra stud at every corner and opening: Add 2 to 3 studs per opening and per corner. On a house with fifteen openings that is forty pieces the spacing calculation missed.
Ordering deck boards by nominal width: A 5/4 by 6 board is 5.5 inches wide, and with a 3/16 inch gap it covers 5.69. Using 6 inches undercounts by about 5%.
Buying all one length: Cut lists usually want a mix. Work out which stock lengths your dimensions divide into cleanly before you order.