Roofing calculators

How to choose a calculation

Start with a roof sketch and mark the horizontal run, vertical rise and sloping length as different measurements. Pitch describes the rise over a specified horizontal run. A common rafter calculation uses that geometry to estimate a length from the numbers you enter. It can help compare a dimension on a drawing with a field measurement or supplier length before ordering.

Record what the horizontal dimension measures: a full building span and one side’s run are different. If the roof has two equal slopes, the common run is generally taken for one side of the sketch. For a roof with different pitches or bearing positions, draw each section separately and use its actual dimensions. Keep any entered overhang distinct from the base run so it is applied once.

A calculated length is a geometry reference. Actual cuts can depend on seat cuts, ridge details, material size, bearing, local rules and the approved structural design. Compare the model to the plan and field measurements before cutting. Confirm rafters, connections and loads with the responsible designer or qualified trade professional.

Roof pitch and common rafter length uses records for horizontal run from bearing reference to ridge reference and Additional horizontal overhang beyond bearing reference. Roof area and roofing squares uses records for extra material allowance for cuts and waste, Coverage printed on one shingle bundle, and Optional price per shingle bundle (0 to omit). Roofing accessories and underlayment uses records for actual sloping roof area, Measured edges requiring starter, Measured hips and ridges requiring cap, and Measured eave/rake edges requiring drip edge.

Start with these calculators

1. Roof pitch and common rafter length — Convert measured roof rise or pitch into slope angle and common-rafter line length.
2. Roof area and roofing squares — Estimate roof surface area, roofing squares and shingle bundles from measured roof planes, a simple pitched footprint or known surface area.
3. Roofing accessories and underlayment — Estimate underlayment rolls, starter bundles, ridge-cap bundles and drip-edge pieces from measured roof area and edge lengths.
4. Slope grade and rise run — Convert measured rise and horizontal run to grade, angle and sloping length, or find rise from a supplied grade.
5. Right triangle lengths and angles — Solve a right triangle from two legs, a hypotenuse and leg, or a horizontal leg and angle.