How this calculator works
Reach, setback and working length form a right triangle. OSHA describes horizontal setback of approximately one-quarter of working ladder length, giving about 75.52 degrees. For upper-landing access, the selected vertical extension is converted into extra length along the ladder. The result is geometric length, before manufacturer overlap, rung placement, securing and duty-rating requirements.
Formula
working length = sqrt(reach² + setback²); angle = atan(reach/setback); quarter setup: setback = working length/4; extra length = vertical landing extension / sin(angle).
Worked example
A ladder reaching 4 m with a 3 m setback has a 5 m working length and 53.13 degree angle. Under the quarter-length rule a 4 m working ladder has a 1 m setback and 3.873 m reach.
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Frequently asked questions
Is any calculated angle a recommended setup?
No. Geometry mode reports the angle you entered through dimensions. Follow the ladder label, manufacturer instructions and applicable ladder-safety requirements.
How far should a ladder extend above a landing?
The cited OSHA rule requires side rails at least 3 ft above the upper landing, or specified alternative securing and a grasping device when that extension is not possible.
Does total length include extension-ladder overlap?
No. Required overlap and usable length depend on the ladder. Compare this geometric need with the manufacturer usable-length rating.