Lawn slope calculator (% and °)
Work it out for your lawn
Worked example
For a bank that rises 0.9 m over 4 m, and a second section where a phone reads 8°, against a mower rated for 35%:
- Section 1: 22.5% (12.7°).
- Section 2: 14.1% (8°).
- Steepest: section 1, at 22.5% (12.7°). A mower rated for 35% (19.3°) is within its rating by 12.5 percentage points.
Mower brands usually quote slope in %, while phone level apps and some reviews use degrees, and the two are easy to mix up. A 45° slope is 100%, and 20° is about 36%, not 20%. This calculator converts both ways and checks your steepest section against a mower's rating.
How it works
- Rise and level distance: slope % = rise ÷ level distance × 100.
- Rise and distance along the ground: we work out the level distance first (Pythagoras), then the same sum.
- Degrees: % = tan(angle) × 100, and back again with the inverse.
Measure the steepest part of the lawn the mower will cover, not the average. If there's more than one steep bit, add each as a section and the calculator flags the steepest.
FAQs
How do I measure the rise?
Hold a string or a straight piece of timber level from the top of the slope, with a spirit level on it, and measure down to the grass at the far end. Or lay your phone on a straight board on the slope and read the angle from a level app.
Why leave a margin below the rated slope?
Rated slopes are usually for dry, firm grass. Wet grass and soft ground make wheels slip, so a slope right at the limit may be fine in summer and a struggle in autumn.
Read the guide: Robot mowers for slopes
More tools
- Boundary wire or wire-free? DeciderAnswer six questions about your garden and see which navigation suits it: boundary wire, RTK satellite, camera vision, LiDAR or a hybrid, with the reasons and the trade-offs.
- Lawn area calculatorMeasure your lawn in m² from simple shapes or points round the edge, across several zones, minus beds and patios. The figure every robot mower spec is rated against.
- Which robot mower fits my lawn?Tell us your lawn's size, zones, steepest slope, narrowest passage and surroundings. We'll show which navigation tech suits it and which UK models are rated to cover it, each with its specs checked date.