Sight and hold this level with a vertical tree...

or a corner of a building...

or a fence post

15°

Use this page as a guide to determine slopes where you may not operate safely.

WARNING: Do not operate your lawn mower on such slopes. Do not mow on inclines with a slope in excess of 15 degrees (a rise of approximately 2-1/2 feet every 10 feet). A riding mower could overturn and cause serious injury. Operate riding mowers up and down slopes, never across the face of slopes. Operate walk-behind mowers across the face of slopes, never up and down slopes.

Section 2 — Important Safe Operation Practices