Calculate roof pitch as an angle, ratio and slope multiplier — enter the rise and run, or the pitch, to find the roof angle and true roof area factor.
Enter rise and run (e.g. 4 and 12 for a 4:12 pitch), or type an angle to convert back.
| Item | Value |
|---|
Roof pitch describes how steep a roof is. It is written as a ratio of vertical rise to horizontal run — a "4:12" pitch rises 4 units for every 12 units across. Pitch can also be expressed as an angle in degrees, and as a slope multiplier used to turn a roof’s flat footprint into its true, larger surface area.
| Pitch | Angle | Area multiplier |
|---|---|---|
| 3:12 | 14.0° | ×1.031 |
| 4:12 | 18.4° | ×1.054 |
| 6:12 | 26.6° | ×1.118 |
| 9:12 | 36.9° | ×1.250 |
| 12:12 | 45.0° | ×1.414 |
Say your roof is a 4:12 pitch and the building footprint under it is 100 m². The calculator gives a slope multiplier of about 1.054 for a 4:12 pitch. Multiply the footprint by the multiplier: 100 × 1.054 = 105.4 m² of actual roof surface. That true area — not the flat footprint — is what you use to order roofing materials like shingles, tiles or metal sheeting.
Roof pitch can be expressed three ways, and it helps to understand how they relate. The traditional builder’s notation is a ratio of rise to run, like 4:12, meaning the roof rises 4 units for every 12 units it runs horizontally. The same slope can be stated as an angle in degrees — a 4:12 pitch is about 18.4° — which is useful for cutting timber and setting out. It can also be given as a percentage grade, found by dividing rise by run, so 4:12 is a 33% grade. Beyond describing steepness, pitch has a practical effect on materials through the slope multiplier: because a sloped surface is longer than its flat shadow on the ground, a steeper roof has proportionally more area to cover. This is why two houses with identical footprints can need very different amounts of roofing if their pitches differ — and why estimating from the footprint alone, without applying the pitch, leads to under-ordering.
How do I calculate roof pitch?
Divide the vertical rise by the horizontal run and take the arctangent to get the angle. For example, a roof that rises 4 units over a 12-unit run is a 4:12 pitch, which is 18.4 degrees. Enter the rise and run above and the calculator gives the angle, ratio and area multiplier.
What does a 4:12 roof pitch mean?
It means the roof rises 4 units vertically for every 12 units of horizontal distance. That works out to an angle of about 18.4 degrees — a common, moderate slope for residential roofs.
What is a roof pitch multiplier?
The slope multiplier converts a roof’s flat footprint area into its actual sloped surface area. A 4:12 pitch has a multiplier of about 1.054, so the true roof area is 5.4% larger than the footprint. It is essential for estimating roofing materials.
How do I convert roof pitch to degrees?
Take the arctangent of rise divided by run. A 6:12 pitch is arctan(6/12) = 26.6 degrees. You can also enter an angle in the calculator above to convert it back to a rise-and-run ratio.
How do I calculate roof pitch?
Divide the vertical rise by the horizontal run and take the arctangent for the angle. A roof rising 4 units over a 12-unit run is a 4:12 pitch, or about 18.4°.
What does a 4:12 roof pitch mean?
It rises 4 units for every 12 units of horizontal run — an angle of about 18.4°, a common moderate slope for houses.
What is a roof pitch multiplier?
It converts a roof’s flat footprint into its true sloped area. A 4:12 pitch has a multiplier of about 1.054, so the real roof area is 5.4% larger than the footprint.
How do I convert roof pitch to degrees?
Take the arctangent of rise ÷ run. A 6:12 pitch is arctan(6/12) = 26.6°. You can also enter an angle above to convert it back to a ratio.
Why does pitch matter for ordering materials?
A steeper roof has more surface area than its footprint suggests. Using the pitch multiplier gives the true area, so you order enough shingles, tiles or sheeting instead of coming up short.