Ladder angle and ladder size calculator
Where to put the foot of an extension ladder, how long the ladder must be, and which duty rating you need.
How it works
OSHA requires non-self-supporting ladders to be set so the base is one quarter of the working length away from the support. That is the 4:1 rule, about 75.5°. If you will step onto a roof or platform, the side rails must extend at least 3 feet above the landing. Duty ratings come from ANSI A14. Count your weight plus clothing, tools and materials.
Quick reference
| Type III | 200 lb | Light household |
| Type II | 225 lb | Medium duty |
| Type I | 250 lb | Heavy duty |
| Type IA | 300 lb | Extra heavy duty |
| Type IAA | 375 lb | Special duty |
Ladders are the single biggest cause of emergency room visits among the tools on this site.
Questions
Is there a quick check for the angle?
Stand at the foot with your toes against the rails and stretch your arms out. Your palms should just reach the rung at shoulder height.
What about stepladders?
Stepladders must be fully opened with the spreaders locked. Do not stand on the top cap or the top step.
Sources
Injury data for these tools
ER visits in 2025