How to Measure Roof Trusses
Measuring for a truss order means capturing four field numbers accurately: span (outside wall to outside wall), pitch (rise per 12" of run), existing truss spacing if replacing trusses, and overhang. Enter your field measurements below to check them against expected chord lengths.
Check Your Field Measurements
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How to Measure Span, Pitch, and Spacing On Site
Measure span at the top plate — outside face of exterior wall to outside face of the opposite exterior wall — not at the foundation, which can differ slightly from the framed wall width. Take the measurement at both ends of the building and in the middle; if they differ by more than an inch, the building is out of square and your supplier needs to know before cutting trusses.
To measure existing pitch without climbing on the roof, hold a level horizontally against the fascia or a rafter, measure 12 inches along the level, then measure the vertical distance down to the roof surface at that 12" mark — that vertical number is your pitch (e.g., 6 inches down at 12" out is a 6/12 pitch).
For truss spacing on an existing roof, measure center-to-center between two adjacent trusses at the top plate, not edge-to-edge — this is the number your new trusses need to match if you are replacing or adding to an existing run.
Frequently Asked Questions
Where exactly do you measure roof span?
Measure span at the top wall plate, from the outside face of one exterior wall to the outside face of the opposite exterior wall — not at the foundation or roofline, which can differ from the actual framed width.
How do you measure roof pitch without a pitch gauge?
Hold a level horizontal against the roof, measure exactly 12 inches along it, then measure straight down to the roof surface at that point — that vertical measurement in inches is your pitch (rise per 12" of run).