Roof Pitch Calculator
Calculate roof pitch from rise and run. Get X/12 pitch, angle, slope %, rafter length, and the pitch multiplier.
Roof pitch calculator
What is roof pitch?
Roof pitch is the amount a roof rises vertically for every 12 inches of horizontal run. A 6/12 roof rises 6 inches for every 12 inches of run and has an angle of about 26.57°. The same geometry can be written as a slope percentage (50%) or as a rafter multiplier (about 1.118).
How to Use the Roof Pitch Calculator
- Enter the vertical rise.
- Enter the horizontal run in the same unit.
- Read the X/12 roof pitch.
- Check the angle and slope percentage.
- Use rafter length or the pitch multiplier if you need them.
You can also start from an X/12 pitch, an angle in degrees, or a slope percentage. The other values update from the same rise/run ratio.
Roof Pitch Formula
All results come from one ratio: rise ÷ run. Rise and run must use the same unit.
- Pitch:
(rise ÷ run) × 12, shown as X/12. - Angle:
atan(rise ÷ run) × 180 ÷ π. - Slope %:
(rise ÷ run) × 100. - Rafter length:
√(rise² + run²). - Multiplier:
√(1 + (rise ÷ run)²). Multiply a simple horizontal footprint by this factor to estimate one sloped roof plane.
Reverse conversions use the same ratio: rise per 12 = 12 × tan(angle), or 12 × (slope% ÷ 100).
Common Roof Pitch Examples
4/12 roof pitch
Rise 4 in · Run 12 in · Angle 18.43° · Slope 33.33% · Multiplier 1.054
6/12 roof pitch
Rise 6 in · Run 12 in · Angle 26.57° · Slope 50% · Multiplier 1.118
8/12 roof pitch
Rise 8 in · Run 12 in · Angle 33.69° · Slope 66.67% · Multiplier 1.202
12/12 roof pitch
Rise 12 in · Run 12 in · Angle 45° · Slope 100% · Multiplier 1.414
Roof Pitch Conversion Chart
Calculated values for 1/12 through 12/12. Use this as a roof pitch to degrees and slope-percentage reference, not as a substitute for measuring the roof.
| Roof pitch | Angle | Slope % | Multiplier |
|---|---|---|---|
| 1/12 | 4.76° | 8.33% | 1.003 |
| 2/12 | 9.46° | 16.67% | 1.014 |
| 3/12 | 14.04° | 25% | 1.031 |
| 4/12 | 18.43° | 33.33% | 1.054 |
| 5/12 | 22.62° | 41.67% | 1.083 |
| 6/12 | 26.57° | 50% | 1.118 |
| 7/12 | 30.26° | 58.33% | 1.158 |
| 8/12 | 33.69° | 66.67% | 1.202 |
| 9/12 | 36.87° | 75% | 1.25 |
| 10/12 | 39.81° | 83.33% | 1.302 |
| 11/12 | 42.51° | 91.67% | 1.357 |
| 12/12 | 45° | 100% | 1.414 |
Pitch, Slope, Angle, and Rise Over Run
People search for a roof slope calculator, roof angle calculator, rise over run calculator, or pitch ratio. Those names describe the same triangle in different units. Pitch is the X/12 ratio used on U.S. plans. Angle is that slope in degrees. Slope percentage is rise ÷ run × 100. The rafter multiplier, also called a slope factor, converts a flat footprint into sloped-plane area for simple geometry.
How to Measure Roof Pitch
Place a level so it reads horizontal, mark 12 inches of run along the level, then measure the vertical rise at the 12-inch mark. Six inches of rise over that 12-inch run is a 6/12 pitch.
Do not climb onto a roof just to measure pitch. When possible, measure from an attic, accessible framing, drawings, or another safe location.
When to Use These Results
- Checking a stated roof pitch on plans
- Converting pitch to degrees or slope percentage
- Estimating rafter length from rise and run
- Applying a pitch multiplier before a roof-area takeoff
- DIY planning before you talk to a roofer
This is a geometry planner. It is not structural engineering, a building-code check, or manufacturer approval. Continue with the Roof Area Calculator when you have a footprint, then the Roofing Shingle Calculator or Metal Roofing Calculator for materials.
Common Roof Pitch Calculation Mistakes
- Swapping rise and run — rise is vertical; run is horizontal.
- Using the full building span — a simple gable run is usually half the span, not wall to wall.
- Mixing units — inches and feet cannot be mixed in one ratio.
- Confusing angle with pitch — 6/12 is not 6°.
- Treating slope % as X/12 — 50% is 6/12, not 50/12.
- Assuming every roof is 6/12 — measure or read the plans.
- Using the multiplier as area — it only scales a footprint.
- Rounding too early — convert first, then round the displayed result.
Roof Pitch FAQ
What is roof pitch?
Roof pitch is the vertical rise for every 12 units of horizontal run, written as X/12. It describes how steep the roof plane is.
How do I calculate roof pitch from rise and run?
Divide rise by run and multiply by 12. Rise 6 and run 12 give (6 ÷ 12) × 12 = 6/12. Rise and run must use the same unit.
What does 6/12 roof pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run. That is about 26.57° and a 50% slope.
What angle is a 4/12 roof?
About 18.43°. The slope is 33.33% and the multiplier is about 1.054.
What angle is a 6/12 roof?
About 26.57°. The slope is 50% and the multiplier is about 1.118.
What angle is an 8/12 roof?
About 33.69°. The slope is 66.67% and the multiplier is about 1.202.
What angle is a 12/12 roof?
Exactly 45°. The slope is 100% and the multiplier is about 1.414.
How do I convert roof pitch to degrees?
Degrees = atan(rise ÷ run) × 180 ÷ π. For an X/12 pitch, that is atan(X ÷ 12) in degrees.
How do I convert degrees to roof pitch?
Rise per 12 = 12 × tan(angle). A 45° roof is 12/12.
What is roof slope percentage?
Slope % = (rise ÷ run) × 100. A 6/12 pitch is a 50% slope. That is not the same number as the X/12 pitch.
What is the roof pitch multiplier?
√(1 + (rise ÷ run)²). Multiply a simple horizontal footprint by this factor to estimate one sloped roof plane. It is not the roof area by itself.
How do I calculate rafter length from roof pitch?
Rafter length = √(rise² + run²) when rise and run are the actual triangle sides. If you only know pitch, enter a horizontal run and the calculator scales it by the multiplier.
What is the difference between roof pitch and roof slope?
They describe the same steepness. Pitch is usually X/12 on U.S. plans. Slope is often a percentage or an angle in degrees.
Can I calculate roof pitch without climbing on the roof?
Yes. Measure from an attic, accessible framing, or drawings when you can. Do not climb onto a roof just to take a pitch reading.