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Slope, pitch
& falls calculator

BETA

Calculate slope, pitch and falls. Input through any two of rise, going and angle.

Results from brickdims.com tools are indicative only. Using this site does not create a professional relationship or duty of care. Not a substitute for professional advice or formal compliance sign-off.

Enter any two values

Pitch angle
RiseGoingSlope
Enter any two values

Common gradients

Click a row to apply that gradient.

ApplicationGradient (1:x)AnglePercentage
Roof drainage (min)1:800.72°1.25%
Paved drainage (min)1:600.95°1.67%
Drainage channel (typical)1:401.43°2.5%
Gentle pedestrian slope1:202.86°5%
Steeper pedestrian slope1:124.76°8.33%
Steps / stairs (approx.)1:226.6°50%
45° slope1:145°100%

Ramp gradients (1:12–1:20) removed from this table. Use the Ramp & Landing calculator → for AD M reference checks on flights, landings and gradients.

FAQs

How do I convert a gradient to degrees?

The angle is the inverse tangent of rise divided by run. A 1:40 fall is arctan(1/40), or about 1.43 degrees.

What is the difference between a ratio, a percentage and an angle?

They describe the same slope three ways. A ratio of 1:50 means 1 unit of rise for every 50 of run. As a percentage that is 1 ÷ 50 × 100 = 2%, and as an angle it is about 1.15 degrees.

How do I work out the rise from a roof pitch?

Multiply the horizontal run by the tangent of the pitch angle. A 30 degree pitch over a 4m run rises 4000 × tan(30°), or about 2309mm.

What fall does a flat roof need?

BS 6229:2025 sets a minimum finished fall of 1:80 for most flat roofs. The design fall needs to be steeper to allow for deflection and building tolerances: 1:60 is a common starting point, with 1:40 where the deck deflects more, and the standard now expects the figure to come from structural analysis or survey.

Related toolsRamp and landing·Pythagoras