What does a roof pitch like 6/12 mean?

It means the roof rises 6 units for every 12 units of horizontal run — 6 inches of rise per foot, or 500 mm per metre. Pitch is always expressed against a run of 12, so a 6/12 and a 3/6 are the same slope written differently. This tool reduces whatever rise and run you enter to the /12 form.

How do I convert roof pitch to degrees?

Take the arctangent of rise divided by run. A 6/12 pitch is arctan(6 ÷ 12) = arctan(0.5) ≈ 26.6°. The tool shows the angle, the grade percent and the /12 pitch together, so you can hand over whichever one the next trade wants.

What is the rafter multiplier?

It is how much longer the sloping rafter is than the flat run beneath it. For a 6/12 the multiplier is about 1.118, so a rafter over a 12-foot run is roughly 13.4 feet before you add the overhang (over a 3.6 m run, about 4.02 m). It comes straight from the triangle: multiplier = √(rise² + run²) ÷ run.

Is pitch the same as grade or slope?

They describe the same steepness in different languages. Pitch is rise per 12 of run, grade is rise ÷ run as a percentage, and the angle is that same ratio in degrees. Roofers talk in /12, earthworks talk in percent, and a protractor reads degrees — this tool gives you all three at once.

Roof pitch calculator

Hauteur (verticale)

Longueur horizontale

Entrez la hauteur et la longueur horizontale réelles — n’importe quelle unité, pourvu que ce soit la même. La pente est toujours donnée pour une longueur horizontale de 12.

6/12 de pente

Garder ces résultats

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These figures describe the slope you enter. They do not size a rafter or judge whether a roof will carry snow, wind or its own weight — that is a structural matter for your plans or an engineer. Confirm the pitch against the actual roof.

Enter the rise and the run and you get the pitch as a /12 figure, the angle in degrees, the grade as a percentage, the reduced ratio and the rafter multiplier. All of them are the one ratio, rise over run, expressed the way each trade prefers.

Exemple détaillé

A roof that rises 6 ft over a 12 ft run is a 6/12 pitch. As an angle that is arctan(6 ÷ 12) ≈ 26.6°, or a 50% grade. The rafter multiplier is √(6² + 12²) ÷ 12 ≈ 1.118, so the rafter over that run is about 13.4 ft before the overhang.

In metric: 1.8 m of rise over a 3.6 m run is the same 6/12 — 500 mm per metre, 26.6°, a 50% grade — and the rafter over that run is 3.6 × 1.118 ≈ 4.02 m before the overhang.

Sur le chantier

Matching an addition to the existing roof. Nobody has the drawings. Hold a 2 ft level flat against the shingles, level it, and measure straight down from the 12 in mark to the roof: 5 in. That is 5/12 — 22.6°, a 41.7% grade — and the addition's rafters get cut to it. Measuring along the slope instead of level is the mistake that gives you a roof a couple of degrees flatter than the house. With a metric level, mark 1,000 mm along it instead: a 417 mm drop is the same 5/12.

The designer said 30 degrees. The framing crew does not cut in degrees. tan(30°) = 0.577, × 12 = 6.93 — so 7/12, near enough, and the speed square goes to 7. Put the rise as 6.93 and run as 12 in the tool and it shows the whole family: 6.93/12, 30.0°, 57.7% and a 1.155 multiplier.

Shingles from the footprint. A 30 × 40 house at 6/12: the footprint is 1,200 sq ft, the roof is 1,200 × 1.118 = 1,342 sq ft, and with 2 ft overhangs all round the footprint grows to 34 × 44 = 1,496 → 1,672 sq ft of roof. Roofing sells by the "square" of 100 sq ft, so that is 16.7 squares before waste, and the steeper the pitch the more squares the same house takes. In metric: a 9 × 12 m house is 108 m² of footprint, 120.7 m² of roof at 6/12; with 600 mm overhangs it is 10.2 × 13.2 = 134.64 m² → about 150.5 m² of roof.

Exercez-vous

Quick referencefor slope

Pitch to degrees: 2/12 = 9,5° · 3/12 = 14,0° · 4/12 = 18,4° · 5/12 = 22,6° · 6/12 = 26,6° · 8/12 = 33,7° · 10/12 = 39,8° · 12/12 = 45°
Pitch to grade: pitch ÷ 12 × 100 — 6/12 is 50%, 4/12 is 33%
Degrees to pitch: tan(angle) × 12 — 30° ≈ 7/12
Roof area: footprint × multiplier (6/12: × 1.118; 8/12: × 1.202)
A roofing square: 100 sq ft of roof
Métrique: a 6/12 is a 1:2 slope, 500 mm rise per metre
Pitch to rise per metre: 4/12 = 333 mm · 6/12 = 500 mm · 8/12 = 667 mm · 12/12 = 1 000 mm

Mistakes to catchbefore you trust the number

Measuring the rise from the plate to the peak of the sheathing, not to the top of the rafter — the pitch is the rafter line, and the difference is the sheathing thickness times the multiplier.
Confusing pitch with slope in the old sense: some drawings write a pitch as a fraction of the span (a 1/4 pitch is a 6/12 slope). This tool works in rise per 12 of run.
Holding the level along a bowed rafter; use a straight edge on the roof plane, and take the rise at the 12 in mark.

What an inspector looks forthe building inspector, and the roofing manufacturer's warranty behind them

On this part of the job

The actual pitch of the roof against the minimum the covering you are installing is approved for — that figure is on the product's own installation instructions, and a covering laid below its minimum slope is both a fail and a void warranty.
Underlayment and ice-and-water membrane where the slope and the climate call for them, at the coverage the instructions state.
That the pitch used to size the rafters or trusses matches the roof as built.
Ventilation appropriate to the roof type, intake as well as exhaust.

Have this ready

The covering manufacturer's printed installation instructions, on site.
A pitch reading taken on the rafter or the sheathing, not off the drawing.

Every figure an inspector measures against comes from the code your jurisdiction has adopted, the stamped drawing, or the manufacturer's printed instructions — so none of them are printed here. Look the number up in your own book, type it into the tool, and the arithmetic is yours.

La formule

pitch = (rise ÷ run) × 12 · angle = arctan(rise ÷ run)

Every output is the slope ratio in a different dress: multiply by 12 for pitch, by 100 for grade percent, take the arctangent for the angle, and use Pythagoras over the run for the rafter multiplier. The units cancel in the ratio, which is why pitch is the same whether you measured in feet or metres.

Questions

What does a roof pitch like 6/12 mean?: It means the roof rises 6 units for every 12 units of horizontal run — 6 inches of rise per foot, or 500 mm per metre. Pitch is always expressed against a run of 12, so a 6/12 and a 3/6 are the same slope written differently. This tool reduces whatever rise and run you enter to the /12 form.
How do I convert roof pitch to degrees?: Take the arctangent of rise divided by run. A 6/12 pitch is arctan(6 ÷ 12) = arctan(0.5) ≈ 26.6°. The tool shows the angle, the grade percent and the /12 pitch together, so you can hand over whichever one the next trade wants.
What is the rafter multiplier?: It is how much longer the sloping rafter is than the flat run beneath it. For a 6/12 the multiplier is about 1.118, so a rafter over a 12-foot run is roughly 13.4 feet before you add the overhang (over a 3.6 m run, about 4.02 m). It comes straight from the triangle: multiplier = √(rise² + run²) ÷ run.
Is pitch the same as grade or slope?: They describe the same steepness in different languages. Pitch is rise per 12 of run, grade is rise ÷ run as a percentage, and the angle is that same ratio in degrees. Roofers talk in /12, earthworks talk in percent, and a protractor reads degrees — this tool gives you all three at once.

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