Floor Joist Size, Span and Spacing Table

by Joanna Stewart

Thu, Sep 13, 2018

When building a house or even a deck, it is important to confirm you have the correct joist sizes, spans and spacing before you get started.

While most residential construction uses 2x8 joists with 16 inch spacing, there are many other factors you need to consider when determining the proper joist span length.

Joist span and spacing is set by your local building code. You should check with your local building department for construction requirements in your area. The information included in these charts is derived from the International Residential Code (2012).

Our joist span charts are for wood joists with a maximum dead load of 10 pounds per square foot and a live load of 40 pounds per square foot.

Dead load is the weight of the structure and any fixed items. Live load represents the weight of furniture, snow, etc.

Editor’s Note: This chart is for basic reference only. If you have any questions you should contact an engineer.

Maximum Span of 2x6 Floor Joist

Wood SpeciesSpacing (O.C.)SS Grade#1 Grade#2 Grade#3 Grade
Douglas fir-larch1211-410-1110-98-8
Douglas fir-larch1610-49-119-97-6
Douglas fir-larch249-08-88-16-2
Hem-fir1210-910-610-08-8
Hem-fir169-99-69-17-6
Hem-fir248-68-47-116-2
Southern pine1211-210-1110-99-4
Southern pine1610-29-119-98-1
Southern pine248-108-88-66-7
Spruce-pine-fir1210-610-310-38-8
Spruce-pine-fir169-69-49-47-6
Spruce-pine-fir248-48-18-16-2

Maximum Span of 2x8 Floor Joist

Wood SpeciesSpacing (O.C.)SS Grade#1 Grade#2 Grade#3 Grade
Douglas fir-larch1215-014-514-211-0
Douglas fir-larch1613-713-112-79-6
Douglas fir-larch2411-1111-010-37-9
Hem-fir1214-213-1013-211-0
Hem-fir1612-1012-712-09-6
Hem-fir2411-310-910-27-9
Southern pine1214-814-514-211-11
Southern pine1613-413-112-1010-3
Southern pine2411-811-511-08-5
Spruce-pine-fir1213-1013-613-611-0
Spruce-pine-fir1612-712-312-39-6
Spruce-pine-fir2411-010-310-37-9

Maximum Span of 2x10 Floor Joist

Wood SpeciesSpacing (O.C.)SS Grade#1 Grade#2 Grade#3 Grade
Douglas fir-larch1219-118-517-913-5
Douglas fir-larch1617-416-515-511-8
Douglas fir-larch2415-213-512-79-6
Hem-fir1218-017-816-1013-5
Hem-fir1616-516-015-211-8
Hem-fir2414-413-112-59-6
Southern pine1218-918-518-014-0
Southern pine1617-016-916-112-2
Southern pine2414-1114-713-19-11
Spruce-pine-fir1217-817-317-313-5
Spruce-pine-fir1616-015-515-511-8
Spruce-pine-fir2414-012-712-79-6

Maximum Span of 2x12 Floor Joist

Wood SpeciesSpacing (O.C.)SS Grade#1 Grade#2 Grade#3 Grade
Douglas fir-larch1223-322-020-715-7
Douglas fir-larch1621-119-117-1013-6
Douglas fir-larch2418-515-714-711-0
Hem-fir1221-1121-620-415-7
Hem-fir1619-1118-717-713-6
Hem-fir2417-515-214-411-0
Southern pine1222-1022-521-916-8
Southern pine1620-920-418-1014-6
Southern pine2418-117-515-511-10
Spruce-pine-fir1221-620-720-715-7
Spruce-pine-fir1619-617-1017-1013-6
Spruce-pine-fir2417-014-714-711-0

The most important design choices to consider when building a home are the species and grade of wood that is being used as well as joist size and spacing. These elements will greatly affect how far you can span your joists.

A few of the most common factors that affect joist span include:

Our joist span charts are based on the International Residential Code. While the IRC has been adopted throughout the United States, each county has different building code requirements. Before starting construction on your house consult your local building department.

READ NEXT

Cost to Build a House Home Design Ideas Home Inspection Cost Bedroom Paint Color Ideas Marble Countertops Average Bedroom Size TimberTech vs Trex Uba Tuba Granite Tile That Looks Like Wood Sanded vs Unsanded Grout