Reading the spec sheet

45% or 45°?

Two robot mowers are both advertised with the number 45. One of them climbs roughly twice the pitch of the other. Nothing on either box tells you which is which, and buying the wrong one on a hill wastes several thousand dollars.

Percent and degrees are not the same scale

Percent grade is rise divided by run. Climb 45 feet over 100 feet of ground and that is a 45% grade — about 24 degrees. Degrees measure the angle directly. The two scales cross at exactly one point: 100% grade is 45 degrees.

That crossing point is why the confusion is so expensive. A 45 in degrees is the steepest rating on the consumer market. A 45 in percent is an ordinary flat-lawn machine. The number is identical and the capability is not close.

How to measure your own grade

You do not need survey equipment. Find the steepest run on your lawn, not the average — the mower has to handle the worst part or it strands itself there. Lay a board along the slope, put a level on it, and measure how far you have to lift one end to bring the bubble to centre. That lift divided by the board length, times 100, is your percent grade. A smartphone inclinometer works too, though it usually reports degrees, so check which number you are reading.

Then leave margin. Wet grass, worn treads and a full grass box all cost traction, and a rating is a laboratory ceiling rather than a promise.

Match your own acreage and grade → · Mowers rated for 1 acre →