Roof Pitch Chart
Roof pitch is written as a x:12 ratio, but you often need it in degrees or as a percentage. This chart converts every common pitch, explains what each column means, and shows the quick formula behind it.
By the Calculate My Reno Team / Published
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Roof pitch is the steepness of a roof written as a ratio: the rise in inches for every 12 inches of horizontal run. A 6:12 roof climbs 6 for every 12 across. Because it is a ratio it reads the same in feet or metres, but to set a level, order materials or check a code limit you often need it in degrees or as a percentage. This chart converts them all.
Roof pitch conversion chart
| Pitch (x : 12) | Angle (degrees) | Grade (%) | Slope factor |
|---|---|---|---|
| 1 : 12 | 4.76° | 8.3% | 1.003 |
| 2 : 12 | 9.46° | 16.7% | 1.014 |
| 3 : 12 | 14.04° | 25.0% | 1.031 |
| 4 : 12 | 18.43° | 33.3% | 1.054 |
| 5 : 12 | 22.62° | 41.7% | 1.083 |
| 6 : 12 | 26.57° | 50.0% | 1.118 |
| 7 : 12 | 30.26° | 58.3% | 1.158 |
| 8 : 12 | 33.69° | 66.7% | 1.202 |
| 9 : 12 | 36.87° | 75.0% | 1.250 |
| 10 : 12 | 39.81° | 83.3% | 1.302 |
| 11 : 12 | 42.51° | 91.7% | 1.357 |
| 12 : 12 | 45.00° | 100.0% | 1.414 |
What each column means
- Pitch (x : 12) - the builder’s ratio, rise per 12 of run. The way pitch is quoted in the US and to most timber suppliers.
- Angle - the same slope measured in degrees from horizontal. This is what a digital level or “roof angle” reads, and the form used in the UK, Australia and New Zealand.
- Grade (%) - rise divided by run as a percentage. A 12:12 roof is a 100% grade because the rise equals the run.
- Slope factor - the rafter length per unit of run, and the multiplier that turns a flat footprint area into the real sloping roof area.
The formula behind the chart
Every column comes from one number, the slope ratio (rise ÷ run):
slope ratio = x ÷ 12 (for an x:12 pitch)
angle = atan(slope ratio)
grade % = slope ratio × 100
slope factor = sqrt(1 + slope ratio²)
So a 4:12 pitch is 4 ÷ 12 = 0.333; atan(0.333) = 18.43°; a 33.3% grade; and a slope factor of √(1 + 0.333²) = 1.054.
Reading the chart the other way
If you measured a roof angle with a level and want the x:12 pitch, multiply the tangent of the angle by 12. A 30° roof is tan(30°) × 12 = 6.9, so just under 7:12. The roof pitch calculator converts in both directions and also returns the rafter length for your run.
Slope bands at a glance
- Under 2:12 - near-flat / low slope; use a membrane, not shingles.
- 2:12 to 4:12 - low slope; shingles only with extra underlayment.
- 4:12 to 9:12 - conventional slope; most coverings work normally.
- 9:12 and up - steep slope; needs extra fixings and care to walk.
Next
Not sure of your current pitch? See how to measure roof pitch, then drop the figure into the calculator to get the rafter length and roof area.
Frequently asked questions
What is 4/12 roof pitch in degrees?
A 4/12 (or 4:12) roof pitch is 18.43° from horizontal. The pitch is a ratio - 4 units of rise for every 12 of run - so the angle is the arctangent of 4 ÷ 12, which is 18.43°. As a percentage grade it is 33.3%, and its slope factor is 1.054.
What is 6/12 roof pitch in degrees?
A 6/12 roof pitch is 26.57° from horizontal - the arctangent of 6 ÷ 12 (0.5). It is the most common "medium" residential pitch, a 50% grade, with a slope factor of 1.118.
How do I convert roof pitch to degrees?
Divide the rise by the run to get the slope ratio, then take the arctangent (atan) of it. For an x:12 pitch that is atan(x ÷ 12). So 3:12 is atan(0.25) = 14.04°, 8:12 is atan(0.667) = 33.69°, and 12:12 is atan(1) = exactly 45°. The roof pitch calculator does this both ways.
What pitch is considered a steep roof?
Roofers treat 9:12 (36.87°) and above as steep slope. Below that, 4:12 to 9:12 is conventional slope where most shingles and tiles work normally, 2:12 to 4:12 is low slope, and under 2:12 is near-flat and needs a membrane rather than shingles.
What is the slope factor in the chart?
The slope factor is the rafter length per unit of run, equal to the square root of (1 + slope ratio squared). It is also the roof-area multiplier: multiply the flat footprint area of the roof by the slope factor for the actual sloping surface area. A 6:12 roof has a factor of 1.118, so a 100 m² footprint is about 112 m² of roof.