Ladder Angle Calculator
The ladder angle calculator helps you to measure the angle between the structure and the ladder.
Grade400%75.9638° from horizontal
Angle75.96376°
Ratio1 in 0.25
Rise per 12 of run48the roofing and stair convention
Rise16 ft4.8768 m
Run4 ft1.2192 m
Slope length16.4924 ftalong the surface, not the horizontal
ADA ramp limittoo steepa wheelchair ramp may not exceed 1 in 12, or 8.33%
Maximum ADA run without a landing98 ftand no more than 30 in of rise between landings
Ladder 4:1 rulecorrect ladder anglea ladder should stand one out for every four up — 75.96°
The formula
grade = rise ÷ run × 100%; angle = atan(rise ÷ run)
Four ways to say the same thing
Grade as a percentage, an angle in degrees, a ratio of 1 in N, and rise per 12 of run are all the same quantity dressed differently. Road engineers use per cent, roofers use rise per 12, drainage uses 1 in N, and only surveyors routinely use degrees.
Note that a 100% grade is 45°, not vertical. The percentage is rise over run, not over the slope length, so it has no upper bound — a 200% grade is a perfectly meaningful 63.4°.
Two limits worth remembering: a wheelchair ramp may not exceed 1 in 12, and a leaning ladder wants 1 out for every 4 up, which is about 76°.