Convert a slope between percent grade, angle and ratio (1 : n) — enter rise and run, and read all three. For ramps, drainage, roads, roofs and earthworks.
Grade % = rise / run × 100; angle = arctan(rise / run); ratio = 1 : (run / rise). Reference points: an accessible ramp is often max 1:12 (≈ 8.3%), and minimum pipe drainage is frequently around 1–2%.