Roof Pitch Calculator
Use this free calculator to convert between roof pitch, angle, rise, run, slope percentage, and rafter length.
What is roof pitch?
Roof pitch describes how steep a roof is. In construction, pitch is often written as X:12, which means the roof rises X units vertically for every 12 units of horizontal run. For example, an 8:12 roof rises 8 inches for every 12 inches of run. A pitch calculator helps you quickly convert among common roof slope formats without manual trigonometry.
Why use a pitch calculator?
Whether you are a homeowner, contractor, roofer, or DIY builder, getting pitch right matters for material planning, drainage, appearance, and code compliance. A pitch calculator saves time and reduces mistakes when you need to:
- Estimate rafter lengths for framing.
- Convert roof angle in degrees to a pitch ratio.
- Convert pitch ratio to percent grade.
- Figure out total rise from a known run.
- Order roofing materials more accurately.
Core formulas used in this calculator
1) From rise and run
If you already know rise and run, slope is straightforward:
- Pitch (X:12) = (rise ÷ run) × 12
- Angle (degrees) = arctan(rise ÷ run)
- Grade (%) = (rise ÷ run) × 100
- Rafter length = √(rise² + run²)
2) From pitch and run
If your drawings show something like 6:12 and you know the run:
- Rise = run × (pitch ÷ 12)
- Angle = arctan(pitch ÷ 12)
3) From angle and run
If you know the roof angle directly:
- Rise = tan(angle) × run
- Pitch X = tan(angle) × 12
Common roof pitch reference table
| Pitch | Approx. Angle | Approx. Grade | Typical Use |
|---|---|---|---|
| 3:12 | 14.0° | 25% | Low-slope residential areas |
| 4:12 | 18.4° | 33.3% | Common traditional roof |
| 6:12 | 26.6° | 50% | Popular balance of style and drainage |
| 8:12 | 33.7° | 66.7% | Steeper climates (snow/rain) |
| 12:12 | 45.0° | 100% | Very steep or specialty architecture |
Practical tips before building
- Measure run horizontally, not along the roof surface.
- Check local building codes for minimum slope by roofing material.
- Remember overhang and ridge details can change cut lengths.
- Use a framing square or digital angle finder to verify field measurements.
- Round carefully when ordering materials to avoid shortages.
Frequently asked questions
Is roof pitch the same as roof angle?
Not exactly. Pitch is usually expressed as a ratio (like 6:12), while roof angle is shown in degrees. They describe the same slope, but in different formats.
What is a good roof pitch?
It depends on climate, architecture, and material. Many homes use 4:12 to 8:12. Low-slope roofs need specific waterproofing systems.
Can I use this as a rafter length calculator?
Yes. The result includes rafter length from the rise and run values you provide. For final cuts, include ridge thickness, birdsmouth details, and local framing standards.
Final note
A pitch calculator is a simple but powerful planning tool. By converting between pitch ratio, angle, rise, run, and grade, you can move faster from idea to accurate material estimates and cleaner construction decisions.