Published by BuildCalculators Editorial · Updated 1 October 2026
Roof pitch and rafter length
Roof pitch compares vertical rise with horizontal run. It can be expressed as an angle or as rise per 12 units of run. A rafter calculation then uses the diagonal distance, with an overhang added where required. These figures help plan material lengths and compare options, but do not specify member sizes or connection details.
What a roof calculation cannot decide
Snow, wind, roof covering weight, span, bracing, drainage, ventilation and local code requirements are site-specific. Valleys, hips, dormers, openings and non-standard roof geometry need more than a common-rafter estimate.
Stair rise and run
A straight stair estimate divides total floor-to-floor rise into a workable number of risers, then divides available run across the treads. Small changes can affect headroom, landings, handrails and code compliance. Measure from finished floor level to finished floor level.
For safety-critical work, use the calculator to understand the question and discuss the final design with a qualified professional or local authority.