Joist calculator

16 ft at 16 in on center: 13 joists.

Job sheet

Plumb joist job sheet

16 ft at 16 in on center.

  • Joists13One extra for the end. This count does not pick a size.
Plumb joist job sheet
16 ft at 16 in on center.

Joists: 13 (One extra for the end. This count does not pick a size.)

The end joist

Count = span in inches ÷ spacing, rounded up, plus one. Ceiling joists use the same count. Studs in a wall, which add extras at openings, are studs. The board-foot tally of the stock is board feet. Deck boards on top are deck boards.

FAQ

How many joists for a 16 foot span at 16 inches?

Sixteen feet is 192 inches. 192 divided by 16 is 12 spaces, and the end joist makes 13. A 12 inch spacing on the same span is 17 joists. A 24 inch spacing is 9.

Does this pick the joist size?

No. Span tables in the code decide the depth for the load and the species. This page only counts pieces at the spacing you already chose. Board feet of those pieces are the board-foot page.

Sources

  1. NIST Handbook 44: The count is geometry: one joist at the start, then one more at each spacing across the span.