Lawn Slope Calculator

Slope percentage and degrees are not interchangeable

Slope percent is (rise ÷ horizontal run) × 100. Slope angle is arctan(rise ÷ run), expressed in degrees. For example, a 2-foot vertical rise across a 10-foot horizontal run is 20% grade, or approximately 11.3°.

To measure safely, choose two visible points and measure the vertical height difference and level horizontal separation. Do not assume the distance measured directly along a hillside is the horizontal run. On very steep or inaccessible land, use a qualified professional rather than entering unsafe areas to take measurements.

How to interpret a mower's slope rating

Some manufacturers quote grade, others degrees. A 75% claim corresponds to approximately 36.9°, while 45% corresponds to approximately 24.2°. Different tire sets, dry-versus-wet traction, boundary slopes and navigation systems may change what can actually be operated. Always read the full manual, not only the marketing number.

We use exact configuration claims in the Mower Fit Checker. Even if a calculated slope is numerically below a manufacturer's limit, the result is not permission to operate that machine there.

Measuring slope for a remote-control or robotic mower

Choose a representative stretch of the hill and measure the vertical height gained between its endpoints. Separately measure the horizontal run over the same stretch. The run is the level ground distance, not the tape length laid along the hill's surface. Divide rise by run and multiply by 100 to get percent grade; use the arctangent of that ratio to obtain degrees. These are two ways of expressing the same measured geometry, but the numbers are not interchangeable.

For example, a 3-foot rise across 10 feet of horizontal run is a 30% grade, which is about 16.7 degrees. It is not a 30-degree hill. A 45% manufacturer grade rating is only about 24.2 degrees, not 45 degrees. That difference can change which mower models appear compatible in a first-pass numerical screening.

Measure the steepest section you expect to mow

A long gentle bank may include a short, much steeper transition near a driveway or retaining wall. Check that short section separately. Measure across the direction of machine travel where possible, and consider whether the mower must traverse sideways, turn, stop or reverse on the hill. Manufacturer figures may distinguish safe paths, allowable cross-slope travel, and boundary placement. The number alone cannot account for traction on wet grass or hidden ruts.

Once you have a reliable figure, enter it in the Mower Fit Checker. The model option here is a numeric comparison with published claims, not an operating approval. Consult the full manufacturer's instructions for the exact tire and wheel configuration, and consider professional help where conditions are hazardous.

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