A rafter tables PDF condenses the math of common rafter framing into quick-reference rows you can print and bring to the jobsite. The two most useful kinds in any rafter tables PDF reference are span tables (maximum allowable span by lumber size, spacing, and load) and length tables (rafter length per foot of run by pitch).
This guide walks through both, with a length table for every common pitch and pointers to the IRC R802 span tables for sizing. The full rafter tables pdf reference (length plus span) is included below in printable form for field use.
Rafter length per foot of run
For any pitch, rafter length per foot of run = √(rise² + 144) ÷ 12. This factor multiplied by your run (in feet) gives total rafter length before adjustments for ridge thickness and overhang.
For 4/12: 1.054. For 5/12: 1.083. For 6/12: 1.118. For 7/12: 1.158. For 8/12: 1.202. For 12/12: 1.414.
Example: a 12-foot run at 6/12 pitch gives 12 × 1.118 = 13.42 feet of rafter length, before ridge offset and overhang.
Span tables
Span tables are published in IRC R802 and updated each code cycle. They list maximum allowable span by lumber size, spacing, species/grade, and snow load.
For typical residential framing in moderate snow (20–30 lbs/sq ft), a 2x8 #2 SPF on 16-inch centers spans about 13 feet; a 2x10 spans about 16 feet; a 2x12 spans about 19 feet. Always verify with the actual code table for your jurisdiction.
Tables on the framing square itself
Most quality framing squares have rafter tables stamped on the blade — common rafter length per foot of run, hip and valley rafter lengths, and jack rafter offsets.
Once you can read them, you can lay out any rafter without external tables: find your pitch on the inch markings of the blade, and the corresponding rafter length is printed below.
Need to run the numbers?Use the free roof pitch calculator on the home page to convert pitch to angle, calculate rafter length, or estimate roof area in any unit.