Joist Span Table for Floor Joists

Floor Joist Span Tables for Common Sizes and Species of Wood

Joist span table - use these span tables to determine maximum spans based on the species and grade of lumber, the size of the floor joists, the spacing of the floor joists, and either of these two common design scenarios:

Live load of 30 PSF / a dead load of 20 PSF / and a deflection limit of L/360.
Live load of 40 PSF / a dead load of 10 PSF / and a deflection limit of L/360.

You must determine your actual design requirements based on your local building code for allowable live load, dead load, and deflection.

Floor Joist Diagram

When determining the span of a floor joist, use the horizontal distance between two vertical supports (see diagrams below and above). The span tables on this page are based on the #2 grade of four common species of lumber.

Floor Joist Span Diagram

How to use the Span Tables

Example: In the joist span table below, the highlighted cell (10-5) indicates that a #2 grade 2" x 8" Douglas Fir joist, spaced 24" apart, can have a maximum span of 10 feet - 5 inches (10-5) if designing for a live load of 40 PSF, a dead load of 10 PSF, and a deflection limit of the total span in inches divided by 360.

Floor Joist Span Table

Live Load = 30 PSF, Dead Load = 20 PSF

Size	Spaced (o.c.)	Species/Grade
		S. Pine	Doug. Fir	Hem-fir	S.P.F.
		#2 grade	#2 grade	#2 grade	#2 grade
2" x 6"	12	10-9	11-8	11-0	11-3
	16	9-4	10-1	9-10	9-11
	24	7-7	8-3	8-0	8-1
2" x 8"	12	13-8	14-9	14-4	14-7
	16	11-10	12-9	12-5	12-7
	24	9-8	10-5	10-2	10-3
2" x 10"	12	16-2	18-0	17-6	17-9
	16	14-0	15-7	15-2	15-5
	24	11-5	12-9	12-5	12-7
2" x 12"	12	19-1	20-11	20-4	20-7
	16	16-6	18-1	17-7	17-10
	24	13-6	14-9	14-4	14-7

Live Load = 40 PSF, Dead Load = 10 PSF

Size	Spaced (o.c.)	Species/Grade
		S. Pine	Doug. Fir	Hem-fir	S.P.F.
		#2 grade	#2 grade	#2 grade	#2 grade
2" x 6"	12	10-3	10-9	10-0	10-3
	16	9-4	9-9	9-1	9-4
	24	7-7	8-3	7-11	8-1
2" x 8"	12	13-6	14-2	13-2	13-6
	16	11-10	12-9	12-0	12-3
	24	9-8	10-5	10-2	10-3
2" x 10"	12	16-2	18-0	16-10	17-3
	16	14-0	15-7	15-2	15-5
	24	11-5	12-9	12-5	12-7
2" x 12"	12	19-1	20-11	20-4	20-7
	16	16-6	18-1	17-7	17-10
	24	13-6	14-9	14-4	14-7

The above spans are based on American Softwood Lumber standard sizes.

To calculate maximum joist spans using different design criteria (loading, spacing, grade, etc.) for these species of framing lumber, see the International Residential Code (IRC).

To calculate maximum spans on species not shown above, use the Span Calculator or the Span Tables for Joists and Rafters on the American Wood Council website.

To learn more about framing a floor and general information on floor framing, visit Framing a Floor on mycarpentry.com.