Joist Span Calculator

How far can floor joists span?

Joist size
Spacing on center
Dead load
ft

The table allows

15 ft 7 inmaximum span

From the published residential span table for Douglas fir-larch No. 2 or better, 40 psf live load, L/360. Other species and grades span differently. Confirm against your local code or a licensed professional.

2x10 at 16 in on center, 10 psf deadTable span 15 ft 7 inYour span 14 ftWithin the table span
Your span14 ft
ResultWithin the table span
Spacing16 in on center
Dead load10 psf

Look up the published maximum span for Douglas fir-larch No. 2 floor joists at 40 psf live load.

How it works

This reads the published residential span table for your joist size, spacing and dead load, then compares your span against it.

Before you order

  • Sleeping rooms and other live loads use different tables, so check before you downsize.
  • Span is the clear distance between supports, which is shorter than the joist.
  • Add blocking or bridging where your code asks for it.

Common questions

How far can a 2x10 span at 16 inches?

In this table, 15 feet 7 inches at 10 psf dead load and 14 feet 3 inches at 20 psf.

Does this work for other species?

Only for Douglas fir-larch No. 2 or better. Other species have their own table values.