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Roof Pitch Calculator

Roof pitch to degrees, grade and slope factor.

Your measurementsEvery assumption editable01

Vertical rise per 12 inches of horizontal run.

Normally 12. Change it only if you measured over a different distance.

Pitch and slopeCalculated live02

Result

26.57degrees

6/12 pitch — 26.57°

Pitch6 in rise over 12 in run
6 / 12
Angle
26.565°
Grade
50%
Slope factormultiply footprint area by this for true roof area
× 1.118

The slope factor is the number to keep. Multiply a roof's footprint area by it and you have the actual sloped surface — a 6/12 roof is about twelve per cent larger than the plan it sits on, and a 12/12 is over forty per cent larger.

Pitch is conventionally expressed over a twelve inch run, which is why it reads as x/12. Measuring over a different run works fine; the result is normalised back to twelfths above.

Above about 6/12 a roof cannot be walked unaided. That is a working threshold rather than a code line, but it is the point at which fall protection stops being optional.

Enter rise over run and get the angle, the grade and — the figure worth keeping — the slope factor that converts a roof's footprint into its actual sloped area.

Why use this tool?What it does differently03

Why use this tool?

Slope factor given

Multiply footprint area by it for true roof area. A 6/12 roof is 12% larger than the plan beneath it.

Degrees and grade

The same slope expressed three ways, since specifications use all of them.

Any measured run

Pitch is conventionally over 12 in, but measure over whatever suits and it normalises back.

Walkability flagged

Above roughly 6/12 a roof cannot be walked unaided.

How this worksThe method04

How this roof pitch calculator works

The angle is the arctangent of rise over run, converted from radians to degrees. Grade is the same ratio expressed as a percentage.

The slope factor is the hypotenuse of the rise-and-run triangle divided by the run — geometrically, how much longer the sloped surface is than its horizontal projection. That is the number that turns a plan area into a real one.

Pitch is conventionally written over a twelve inch run, which is where the x/12 notation comes from. Measuring over a different run works and the result is normalised back to twelfths.

How to use itStep by step05

How to use it

  1. Step 1: Measure the rise

    Safest from inside the loft: hold a level horizontally against a rafter and measure vertically at a known distance along it.

  2. Step 2: Enter the run

    Normally 12 inches. Change it only if you measured over a different distance.

  3. Step 3: Take the slope factor

    Multiply your roof footprint by it for the actual surface area.

  4. Step 4: Check walkability

    Above about 6/12, plan for fall protection rather than confidence.

Example usageWorked figures06

Example usage

A common residential pitch
6 in of rise over 12 is 26.57°, a 50% grade, and a slope factor of 1.1180 — the roof is 11.8% larger than its footprint.
A steep roof
12/12 is exactly 45°, a 100% grade, and a slope factor of 1.4142. The roof surface is over forty per cent larger than the plan.
A low slope
3/12 is 14.04°, a 25% grade, and a slope factor of 1.0308 — barely three per cent more area than the footprint.
Frequently asked questionsCommon questions07

Frequently asked questions

What is a 6/12 roof pitch in degrees?

26.57 degrees. The pitch notation means six inches of rise for every twelve inches of horizontal run.

What is a roof slope factor?

The multiplier that converts footprint area into actual sloped roof area. At 6/12 it is 1.1180, so the roof is about twelve per cent larger than the plan beneath it.

How do I measure roof pitch safely?

From inside the loft. Hold a level horizontally against a rafter, measure twelve inches along it, then measure vertically from that point up to the rafter. That vertical figure is the rise.

What pitch can I walk on?

Up to about 6/12 most people can walk with care. Above that you are on a surface you cannot stand on unaided, and fall protection stops being a judgement call.

Is pitch the same as grade?

They describe the same slope differently. Pitch is rise over a twelve inch run; grade is the same ratio as a percentage. A 6/12 pitch is a 50% grade.

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