Roof Gradient Calculator
Convert a measured roof slope between rise/run, degrees, x:12, percentage and 1:n. Add a horizontal plan area or run for sloping area or length. This is a geometry calculator; it does not approve a covering or design a roof.
- Free to use
- No sign-up
- Runs in your browser
Roof gradient calculator
Geometry only. No roof-covering approval, structural design, phone measurement or material order quantity is supplied. A common-rafter slope length excludes overhang and cuts.
Roof Pitch Reference Pack
Optional editable files: two calculating spreadsheets and two Word records. All four PDFs and the web calculator are free. No roof design, professional survey or covering approval.
- Roof slope conversion
- Roof area planning
- Product specification check
- Observation and handoff record
Formats: PDF, XLSX, DOCX. Instant download after payment (link valid 72 hours, up to 5 downloads). AI-assisted: AI tools were used to help draft these materials.
$3.00 USD, one-time
- Instant download
- 7-day refund
- Secure checkout by Stripe
7-day money-back guarantee. Full refund within 7 days of purchase, even after you download.
Free sample: Product specification check (PDF, 57 KB)
Full refund within 7 days — see the refund policy and license.
One slope, consistent units
Use vertical rise divided by horizontal run, with both in the same length unit. Plan area means the horizontal projection of one roof plane. For planes with different slopes, calculate each separately and add only areas expressed in the same unit.
Worked example
For a rise of 7 over a run of 12, the angle is 30.256437 degrees and the slope factor is 1.157704 when displayed to six decimals. With 600 sq ft of horizontal plan area, unrounded calculation gives 694.622199 sq ft of sloping area. A horizontal run of 14 ft gives 16.207851 ft along that plane, before overhang or cuts.
Formulas
- Slope = rise / horizontal run. Angle = arctan(slope).
- Pitch per 12 = slope x 12; gradient percentage = slope x 100.
- For a nonzero slope, the run n in 1:n is 1 / slope. A flat slope has no finite 1:n value.
- Slope factor = sqrt(1 + slope squared). Multiply horizontal plan area or run by the unrounded factor.
Input and output limits
Rise, run, pitch and percentage inputs accept values up to 1 billion; angles must be from 0 up to, but not including, 89.9 degrees. Horizontal run and ratio denominators must be positive. Optional area and length may be blank or zero. These are calculation limits, not construction recommendations. Excessively large results are rejected.
Roof-covering suitability needs an exact specification
A single category-wide minimum can be misleading. Marley publishes different limits for named profiles; its concrete Plain tile entry is 35 degrees. GAF R-127 explains special low-slope installation requirements. Consult the current instructions for your exact product and local requirements with a qualified roofer or designer. No pass/fail suitability result is provided here.
Free references and PDFs
Marley product-specific minimum pitches · GAF low-slope shingle bulletin R-127. Sources checked 27 October 2026.
What the optional $3 pack adds
Two calculating Excel worksheets and two editable Word records, plus four manual/reference PDFs and a README: nine files. The conversion workbook has 24 editable pitch rows; the area workbook has 11 rows with explicit area units and a user-chosen allowance. The Word records organize exact-product requirements and observations for professional review.
Scope before purchase
The files do not synchronize or certify suitability. PDFs do not calculate. The area worksheet produces a planning area, not a tile, shingle or bundle order. Confirm actual product coverage, cuts, waste, overhangs and purchase units separately. Phone tilt readings and perspective photographs are not verified measurements; no sensor feature or accuracy claim is included.
Frequently asked questions
How do I convert 6:12 to degrees?
Use arctan(6/12), which gives approximately 26.565051 degrees.
Can the calculator handle a flat slope?
Yes, use zero rise, zero degrees, zero pitch or zero percentage. A flat slope has no finite 1:n ratio.
Does changing ft to m convert the inputs?
No. The selector identifies your input units. Convert the numeric values before changing units; do not mix units within a calculation.
Can I order roofing materials from the area result?
It is geometry only. Confirm product coverage, waste, cuts, overlaps, overhangs and packaging separately.
Will it tell me which roof covering is allowed?
No. Use the current exact-product instructions, local requirements and qualified professional advice.
What is paid and what is free?
The web calculator and all four PDFs are free. The optional $3 ZIP adds two calculating spreadsheets and two editable Word records, with the PDFs and README included.