Ladder Angle & Height Calculator: OSHA 4-to-1 Rule
Find how far to set a ladder from the wall with the OSHA 4-to-1 rule. Get the ladder length, base distance and 75.5° angle, in feet or metres.
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The roofline, gutter or edge of the platform the ladder rests against.
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The 4-to-1 rule for leaning ladders
OSHA's construction standard for portable ladders, 29 CFR 1926.1053(b)(5)(i), says a non-self-supporting ladder is used at an angle such that the horizontal distance from the top support to the foot of the ladder is approximately one quarter of the working length of the ladder. In the field that is 1 foot out for every 4 feet of ladder, which puts the ladder at 75.5 degrees to the ground. The working length is measured along the ladder, from its foot to the point where it touches the support.
How far to set the foot, by ladder length
| Working length | Foot from the wall | Height reached |
|---|---|---|
| 8 ft | 2 ft 0 in | 7 ft 9 in |
| 10 ft | 2 ft 6 in | 9 ft 8 1/4 in |
| 12 ft | 3 ft 0 in | 11 ft 7 3/8 in |
| 16 ft | 4 ft 0 in | 15 ft 5 7/8 in |
| 20 ft | 5 ft 0 in | 19 ft 4 3/8 in |
| 24 ft | 6 ft 0 in | 23 ft 2 7/8 in |
| 28 ft | 7 ft 0 in | 27 ft 1 3/8 in |
| 32 ft | 8 ft 0 in | 30 ft 11 3/4 in |
What ladder you need for a given height
Start from the height of the point of support, the roof edge or the platform you climb onto. If you are climbing onto it, the side rails must extend at least 3 feet above the landing (1926.1053(b)(1)), so add that to the working length.
| Support height | Working length | Foot from the wall | Ladder length with 3 ft above |
|---|---|---|---|
| 8 ft | 8 ft 3 1/8 in | 2 ft 0 3/4 in | 11 ft 3 1/8 in |
| 10 ft | 10 ft 3 7/8 in | 2 ft 7 in | 13 ft 3 7/8 in |
| 12 ft | 12 ft 4 3/4 in | 3 ft 1 1/8 in | 15 ft 4 3/4 in |
| 14 ft | 14 ft 5 1/2 in | 3 ft 7 3/8 in | 17 ft 5 1/2 in |
| 16 ft | 16 ft 6 1/4 in | 4 ft 1 5/8 in | 19 ft 6 1/4 in |
| 18 ft | 18 ft 7 1/8 in | 4 ft 7 3/4 in | 21 ft 7 1/8 in |
| 20 ft | 20 ft 7 7/8 in | 5 ft 2 in | 23 ft 7 7/8 in |
Setting a ladder up safely
- Stand the ladder on firm, level ground, and keep the rails clear of overhead power lines.
- Secure the top where you can, and keep three points of contact while you climb.
- Extension ladders are labelled by their fully extended length; the overlap between sections shortens the length you can use, so read the label before you choose one.
- This rule is for leaning ladders. A stepladder is used fully opened with its spreaders locked, and fixed ladders have separate requirements.
This tool is a setup aid based on the standard's wording, not a substitute for your site's procedures or the ladder maker's instructions.
Frequently asked questions
- What is the OSHA 4-to-1 ladder rule?
- OSHA's rule for portable ladders that lean on a support (29 CFR 1926.1053(b)(5)(i)) says the horizontal distance from the top support to the foot of the ladder should be approximately one quarter of the working length of the ladder. That is 1 foot out for every 4 feet of working length, an angle of about 75.5 degrees with the ground. The working length is measured along the ladder, from its foot to the point where it touches the support.
- How far from the wall should a 20-foot ladder be?
- 5 feet. One quarter of 20 feet is 5 feet, and a ladder set that way reaches a height of about 19 ft 4 3/8 in (19.36 ft) on the wall. The ladder, the wall and the ground form a right triangle, so the reach is the square root of 20² minus 5².
- What size ladder do I need to reach a 12-foot roof edge?
- For a support point 12 feet up, the working length is about 12 ft 4 3/4 in (12.39 ft) and the foot goes about 3 ft 1 1/8 in (3.10 ft) from the wall. If you are climbing onto the roof, OSHA requires the side rails to extend at least 3 feet above the landing (1926.1053(b)(1)), so the ladder needs to be at least 15 ft 4 3/4 in (15.39 ft) long. Check the label: extension ladders are rated by their maximum extended length, and the overlap between sections shortens the usable length.
- Does the 4-to-1 rule apply to stepladders?
- No. The one-quarter rule is for non-self-supporting ladders, the straight and extension ladders that lean on something. A stepladder stands on its own and is used fully opened with the spreaders locked. Fixed ladders have their own rules in the same standard.
- What happens if the ladder angle is wrong?
- Too steep (foot too close to the wall) and the ladder can tip backwards. Too shallow (foot too far out) and the base can slide out and the rails flex more. The Check a ladder I set up option takes your working length and the measured foot distance and tells you the angle and which way to move the foot. OSHA says the distance should be approximately one quarter, so this is a setup aid, not an inspection.
- Does this work in metres?
- Yes. Pick Metres and every figure is in metres. The ratio is the same, and the 3 foot rail extension becomes 0.9 m, the figure OSHA gives beside it.
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