Example 1 — Roof with a moderate angle
- Rise: 2.8 m
- Half-span: 4.0 m
Roof angle: 34.99°
Slope: 70.0%
This is effectively a 35° roof, which makes it a clear example of the relationship between rise and half-span.
Roof pitch angle
Calculate roof angle from height and half-span, and compare it with slope percentage.
A roof pitch angle calculator lets you move quickly from basic roof dimensions to an angle in degrees. It is a useful tool for roof geometry analysis and comparing different pitch options. Related: ridge height, slope percent.
Results
Enter data and click Calculate.
How the results are calculated
Angle = arctan(rise ÷ half-span); slope % = (rise ÷ half-span) × 100. Optional rafter length = √(half-span² + rise²).
How to use this calculator
- Enter the rise to the ridge or the roof height difference.
- Add the half-span of the roof, which is the horizontal distance from wall to ridge.
- Read the result in degrees.
- If the calculator also shows slope percentage, use both values for easier comparison.
Example scenarios
Example 2 — Gentler roof slope
- Rise: 1.5 m
- Half-span: 3.5 m
Roof angle: 23.20°
Slope: 42.86%
A lower rise with a similar base quickly reduces the angle and changes the overall roof proportions.
Example 3 — Higher roof on a wider base
- Rise: 3.2 m
- Half-span: 5.0 m
Roof angle: 32.62°
Slope: 64.0%
This is a good example of why intuition is not always enough and why calculating the angle makes comparing options easier.
FAQ
How is roof angle calculated?
Most often from the relationship between roof rise and half-span. The result is expressed in degrees.
What is the difference between angle and slope percentage?
They are two ways of describing the same incline. Angle is shown in degrees, while slope percentage is the height-to-horizontal-distance ratio in percent.
Why is half-span used?
Because one roof slope is measured from the wall to the ridge, not across the full building width.
Is this calculator useful in design work?
Yes, as a quick planning tool for comparing options. It does not replace a full design, though.
What causes the most common mistakes?
Entering full span instead of half-span, or confusing rise with diagonal roof length.
Is it useful to know both angle and slope?
Yes. In some situations, degrees are easier to compare; in others, percentage is more practical.
Which calculator should be paired with this one?
Most naturally ridge height and slope percent.
Does a difference of a few degrees really matter?
Yes, because it affects the building form, ridge height, and practical roof performance.