Roof Pitch Calculator

Know the height and horizontal distance from a ladder or plans? Use Rise + Run. Only know the pitch number stamped on your framing square (e.g. "6:12")? Use Pitch + Run. Already measured the actual rafter board? Use Rise + Rafter.

Used only to flag a pitch below the IRC minimum slope for this covering — R905.2.2 for asphalt shingles, R905.10.2 for standing seam. For shingle/panel quantities, use the Shingles calculator.

RiseftVertical height from the top plate to the ridge.RunftHorizontal distance from the outside wall to the center of the ridge.Roof lengthftThe building's length along the eave — how far the rafters repeat.On-center spacinginRafter-to-rafter spacing. 16 or 24 in is standard framing.Overhang runoptionalftHow far the roof extends past the wall — typically 1–2 ft.Ridge board thicknessoptionalinUsually 1.5 in for a standard 2x ridge board.

Rafter sizing (optional)

Recommend the minimum rafter size for the calculated span, or look up a specific size, using the verified IRC rafter span table. Skip this if you just need rafter length and pitch.

Species groupIRC R802 tableType of framing lumber — SPF (spruce-pine-fir) is the most common choice if you're not sure.

Not sure what size lumber to use? Leave this on Auto — it recommends the smallest code-compliant rafter for your span.

Rafter sizeManual lookup rowRafter spacingin on centerRoof live loadpsfWeight code assumes from people/equipment/snow on the roof. Verified table covers 20 psf only — not a snow-load table.Dead loadpsfWeight of the roofing materials themselves. Verified table covers 10 or 20 psf only.

Active project chain

Valid roof results will auto-save roof area into the active project for the next calculators.

Plan for a — ft rafter at a —:12 pitch.

Plan for

Roof results

Warnings

ERROR Enter a roof length greater than zero.
ERROR Rise and run are required for the selected solve mode.
INFO This is a general reference only. Verify local code, loading, and manufacturer requirements.

Detail values

Rise: — ft
Run: — ft
Rafter length: — ft
Ridge-cut rafter length: — ft
Total rafter length (order length): — ft
Pitch: — : 12
Angle: — deg
Recommended rafter size: Data not available for this combination
Span lookup status: —

Assumptions

Pitch warning reference: IRC R905.2.2: asphalt shingles, 2:12 minimum, with double underlayment required from 2:12 up to 4:12
Overhang included in roof area: No
Ridge board thickness: 1.5 in (1.5 in default matches a standard 2x ridge board)
Rafter span table load basis: IRC "Rafter Spans for Common Lumber Species" table: 20 PSF roof live load, 10 or 20 PSF dead load, L/delta=180, ceiling not attached to rafters. Not a ground-snow-load table.
Rafter span measured as: Horizontal run, wall to ridge — not yet entered. Overhang is a cantilever past the support and is not part of the span, and the table is not indexed by sloped length.

Included: rafter length, rafter size recommendation, pitch/angle.

Not included: labor, permits, engineering review or stamped plans, fasteners and connectors unless explicitly itemized above.

Formula details

Rafter length: sqrt(rise^2 + run^2)
Pitch: (rise / run) x 12
Angle: atan(rise / run) x (180 / pi)
Rafter count: ceil(roofLength / spacing) + 1
Layout arithmetic, not a published figure: one rafter at every on-center position along the plane, plus one to close the last bay. Per single roof plane -- multiply by the number of planes (2 for a gable, more for a hip) for the whole roof.
Ridge-cut rafter length: rafterLength - (ridgeBoardThickness / 2) x (rafterLength / run)
Shortens the theoretical rafter length by the ridge board's half-thickness, projected onto the slope, so the ordered board matches the actual birdsmouth/ridge cut.
Roof plane area: roofLength x (rafterLength + overhangDiagonal)
Single roof plane, including the overhang. Measured on the theoretical rafter length rather than the ridge-cut length: the ridge cut is where the board stops, and the covering runs over it to the ridge centerline.
Soffit area: roofLength x overhangRun
Underside of the overhang only; zero when no overhang is entered.
Rafter span lookup: Use verified IRC "Rafter Spans for Common Lumber Species" table row for species, rafter size, and spacing.
Roof live load 20 PSF, L/delta=180, ceiling not attached to rafters. Not a snow-load table.

Material List

About this calculator

Use this roof calculator to solve common rafter geometry and feed roof area into shingles and sheathing.

FAQ

Can I solve from pitch and run only?

Yes. Pick the pitch-and-run mode and CrewMeasure will calculate rise, rafter length, angle, and roof area.

Does the calculator include overhang?

If you enter an overhang run, the calculator includes its diagonal length in total rafter length, roof area, and soffit area (the underside of the overhang).

What does the pitch warning mean?

It is only a general reference check for a couple common roof coverings. Local requirements still govern.

What is the ridge-cut rafter length?

Rafters don't actually reach the theoretical triangle apex — they're cut short by half the ridge board's thickness at the ridge (the birdsmouth/ridge cut). Ridge board thickness is editable and defaults to 1.5 in, a standard 2x ridge board; the ridge-cut length (not the raw triangle length) is what feeds total rafter length and roof area.

Disclaimer

This is a material estimate and general reference only. Verify local code, loading, and manufacturer requirements.