Slope angle: degrees, percent, rise over run

Worked example

You measure a slope that rises 58 m over a horizontal run of 100 m. The angle is arctan(58 / 100) = 30.1 degrees, which is a 58% grade, or 58 of rise for every 100 across. That lands in the 30 to 45 degree band where, per Avalanche Canada, the vast majority of avalanches take place. A 100% grade is exactly 45 degrees, and a 30 degree slope is a 57.7% grade.

How it works

Slope angle = arctan(rise / run). Percent grade is rise / run x 100, so 100% is 45 degrees. The rise and run must be in the same units and the run is horizontal, not along the snow surface. If you read a clinometer or an app, you already have the angle in degrees and this page converts it to percent.

AvySavvy, from Avalanche Canada, says slope angle is the most significant characteristic of an avalanche slope. The vast majority of avalanches take place on slopes between 30 and 45 degrees; they can happen on slopes of 25 to 30 degrees but are not as common; and on slopes steeper than 45 degrees snow usually slides away frequently, so slabs are less likely to form. It also warns that an avalanche starting in steep terrain can run across a flat slope and even travel uphill, so the slope you stand on is not the only one that matters. The page recommends a clinometer (inclinometer), and smartphone apps do the same job.

Angle is only one factor. Check the avalanche forecast for your area, take an avalanche skills course and travel with trained partners and rescue gear before entering avalanche terrain.

Sources and basis: AvySavvy (Avalanche Canada), “Slope Angle”. Opened 2026-10-08. The arithmetic is standard trigonometry. Safety information only; this tool does not assess avalanche danger.

Planning guide only, not professional, medical or safety advice. Conditions, equipment and ability change real needs; use your own judgment and local guidance.

FAQ

What slope angle do most avalanches happen on?

According to Avalanche Canada’s AvySavvy, the vast majority of avalanches take place on slopes between 30 and 45 degrees, about the steepness of a black run on a ski hill.

Can avalanches happen on slopes under 30 degrees?

Avalanches can happen on slopes between 25 and 30 degrees, but they are not as common. An avalanche that starts on steeper terrain can also run across a flat slope and even travel uphill.

What about slopes steeper than 45 degrees?

AvySavvy says snow on slopes steeper than 45 degrees usually slides away frequently, so slabs are less likely to form. That does not make such terrain safe.

How do I convert percent grade to degrees?

Degrees = arctan(percent / 100). So 100% is 45 degrees and 58% is about 30 degrees. A vertical wall would be an infinite grade. This page converts in either direction.

Does a slope angle tell me if a slope is safe?

No. Angle is one factor. Snowpack, weather, terrain above and below and group decisions matter, so use the avalanche forecast, training and a qualified guide.