Construction Calculators
Rafter Length Calculator
Compute rafter length from rise and run or from roof pitch; estimate truss count from roof length and on-center spacing, plus optional material and installation cost.
Rafter length uses the right-triangle relationship: √(rise² + run²), or run × √(pitch² + 1) when pitch is expressed as rise/run.
Truss count uses your roof length and truss spacing (converted to the same length units), rounded up with an end truss: ceil(length ÷ spacing) + 1.
Expenses can include a per-truss price and optional installation billed at a rate × duration.
I want to calculate...
Calculation should include...
Rise
m
Run
m
Rafter length
m
Leave one field empty to solve it from the other two (right triangle: rafter² = rise² + run²).