Joist Span Table for Floor Joists

Floor Joist Span Tables for various Sizes and Species of Wood

Joist span table - Use these tables to determine floor joist spans based on grade of lumber, size of joist, floor joist spacing, and a live load of 30 lbs/ft² or 40 lbs/ft². These tables can also be used to determine deck joist span.

For example, in the joist span table below, the highlighted cell shows that 2" x 8" Southern Yellow Pine joists, that have a grade of #2, and are spaced 24" apart can have a maximum span of 10 feet - 3 inches (10-3) if designing for a live load of 40 lbs/ft².

Nominal Size	Spacing (o.c.)	Species and Grade of Lumber ( based on 30 lb / ft². Live Load)
		Southern Yellow Pine	Southern Yellow Pine	Douglas Fir	Eastern Spruce
		#1 grade (kiln dried)	#2 grade	#2 grade	Structural
2" x 6"	12	12-6	11-3	12-0	11-0
	16	11-4	10-10	10-11	10-0
	24	9-11	8-8	9-7	8-9
2" x 8"	12	16-6	14-11	15-10	14-6
	16	15-0	13-6	14-5	13-2
	24	13-1	11-6	12-7	11-6
2" x 10"	12	21-0	19-0	20-3	18-6
	16	19-1	17-3	18-5	16-10
	24	16-8	14-7	16-1	14-8
2" x 12"	12	25-7	23-1	24-8	22-6
	16	23-3	21-0	22-5	20-6
	24	20-3	17-9	19-7	17-11

Nominal Size	Spacing (o.c.)	Species and Grade of Lumber ( based on 40 lb / sq. ft. Live Load)
		Southern Yellow Pine	Southern Yellow Pine	Douglas Fir	Eastern Spruce
		#1 grade (kiln dried)	#2 grade	#2 grade	Structural
2" x 6"	12	11-4	10-3	10-11	10-1
	16	10-4	9-4	9-11	9-2
	24	9-0	7-9	8-8	7-11
2" x 8"	12	15-0	13-6	14-5	13-2
	16	13-7	12-3	13-1	12-0
	24	11-11	10-3	11-3	10-6
2" x 10"	12	19-1	17-3	18-5	16-10
	16	17-4	15-8	16-9	15-3
	24	15-2	13-1	14-6	13-4
2" x 12"	12	23-3	21-0	22-5	20-6
	16	21-1	19-1	20-4	18-7
	24	18-5	15-11	17-6	16-3

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

** Note: The data in the floor joist span tables above was obtained from Architectural Drawing and Light Construction by Edward J. Muller.

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