How to Measure Roof Pitch?
Roof pitch angle describes how steep one side of a roof is. It is based on the relationship between 2 measurements:
Run - the horizontal distance
Rise - the vertical height over the distance
Roof pitch can be expressed as a ratio (like 4:12) or converted into degrees (like 20 degrees) when required for calculators or for choosing the right roofing products.
Tools You Will Need:
- Tape Measure
- Spirit Level
- Ladder or safe roof or loft access
- Pen and paper or phone for making notes
Measure Roof Pitch Using Rise and Run
This is the most common and most accurate method of measuring roof angle.
Step 1: Measure the run
Place the spirit level horizontally against the roof slope, and measure a fixed horizontal distance. Common choices are 300mm or 12 inches.
This measurement is your run.
Step 2: Measure the rise:
From the end of the spirit level, measure vertically down to the roof surface.
This vertical distance is the rise.
Step 3: Calculate the pitch
You now have your roof pitch angle as a ratio - Rise: Run
For example, if the rise is 100mm over a 300mm run, the pitch is 1:3.
Convert Roof Angle to Degrees
Some roofing products and calculators require pitch to be entered in degrees rather than a ratio.
Once you have measured rise and run, you can convert this using a roof angle calculator. This removes the need for manual trigonometry and helps avoid errors.
You can calculate pitch in degrees using this tool:
https://www.metal-guttering.co.uk/ridges-valleys
Common Roof Angle Measurement Mistakes to Avoid
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Measuring along the roof slope instead of horizontally
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Using a run that is too short can reduce accuracy
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Mixing units between rise and run
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Estimating pitch by eye.
