The safe angle for a straight or extension ladder is about 75 degrees from the ground, and the easy way to set it is the 4-to-1 rule: for every 4 ft of ladder between its feet and the point where it rests on the wall, set the feet 1 ft out from the wall. That rule is written into the US federal construction safety standard for ladders, 29 CFR 1926.1053. This page has a quick calculator for the base distance and the ladder length you need, a chart for common ladder lengths, and a plain-English summary of the other OSHA ladder rules.
Ladder angle calculator
The 4-to-1 rule explained
OSHA’s wording is that a ladder that is not self-supporting must be set so that the horizontal distance from the top support to the foot of the ladder is about one quarter of the ladder’s working length, the distance along the ladder from its feet to the top support. A ratio of 1 to 4 gives an angle of arccos(1/4) = 75.5° from the ground, and the top support is then 0.968 × the working length above the ground. Steeper than that and the ladder can tip backwards as you climb; flatter and the feet can slide out.
Two quick checks on site: count the rungs (on most ladders they are about 12 in apart, so a ladder resting 16 rungs up the rails needs its feet about 4 ft out), or stand with your toes at the feet and reach forward with straight arms; at about the right angle your hands meet a rung at shoulder height.
Ladder length and base distance chart
| Working length | Base out from the wall | Height of the top support | Highest standing level (top 3 ft not used) |
|---|---|---|---|
| 8 ft | 2.0 ft | 7.7 ft | 4.8 ft |
| 10 ft | 2.5 ft | 9.7 ft | 6.8 ft |
| 12 ft | 3.0 ft | 11.6 ft | 8.7 ft |
| 14 ft | 3.5 ft | 13.6 ft | 10.7 ft |
| 16 ft | 4.0 ft | 15.5 ft | 12.6 ft |
| 20 ft | 5.0 ft | 19.4 ft | 16.5 ft |
| 24 ft | 6.0 ft | 23.2 ft | 20.3 ft |
| 28 ft | 7.0 ft | 27.1 ft | 24.2 ft |
| 32 ft | 8.0 ft | 31.0 ft | 28.1 ft |
| 36 ft | 9.0 ft | 34.9 ft | 32.0 ft |
| 40 ft | 10.0 ft | 38.7 ft | 35.8 ft |
What size ladder to reach a roof
| Eave or landing height | Working length to the edge | Minimum ladder length (3 ft above the edge) | Base out from the wall |
|---|---|---|---|
| 8 ft | 8.3 ft | 11.4 ft | 2.1 ft |
| 9 ft | 9.3 ft | 12.4 ft | 2.3 ft |
| 10 ft | 10.3 ft | 13.4 ft | 2.6 ft |
| 12 ft | 12.4 ft | 15.5 ft | 3.1 ft |
| 14 ft | 14.5 ft | 17.6 ft | 3.6 ft |
| 16 ft | 16.5 ft | 19.6 ft | 4.1 ft |
| 18 ft | 18.6 ft | 21.7 ft | 4.6 ft |
| 20 ft | 20.7 ft | 23.8 ft | 5.2 ft |
| 24 ft | 24.8 ft | 27.9 ft | 6.2 ft |
OSHA ladder requirements (construction)
| Topic | Requirement | 29 CFR section |
|---|---|---|
| Ladder angle | Foot of the ladder out from the top support by about 1/4 of the working length (the 4-to-1 rule); job-made wood ladders with spliced rails: 1/8 | 1926.1053(b)(5)(i)-(ii) |
| Access to a roof or landing | Side rails at least 3 ft above the upper landing, or the top secured to a rigid support with a grab rail | 1926.1053(b)(1) |
| Load | Never more than the maximum intended load or the maker’s rated capacity | 1926.1053(b)(3) |
| Strength | Portable ladders must hold at least 4 times the maximum intended load (3.3 times for extra-heavy-duty type 1A metal or plastic) | 1926.1053(a)(1) |
| Rung spacing | 10 to 14 in centre to centre on portable and fixed ladders; 8 to 12 in on step stools | 1926.1053(a)(3) |
| Footing | Only on stable, level surfaces unless secured; not on slippery surfaces unless secured or fitted with slip-resistant feet | 1926.1053(b)(6)-(7) |
| Traffic | Secure or barricade a ladder in a doorway, passageway or driveway | 1926.1053(b)(8) |
| Stepladders | Do not stand on the top or top step, or climb the rear cross-bracing unless it has steps | 1926.1053(b)(13)-(14) |
| Electrical | Non-conductive side rails where the ladder or worker could contact energized equipment | 1926.1053(b)(12) |
| Climbing | Face the ladder, keep at least one hand on it, and do not carry anything that could cause a fall | 1926.1053(b)(20)-(22) |
| Moving | Do not move, shift or extend a ladder while someone is on it | 1926.1053(b)(11) |
| Inspection | Inspected by a competent person periodically and after any event that could affect it; defective ladders tagged and removed | 1926.1053(b)(15)-(16) |
| When a ladder is required | A stairway or ladder at any point of access with a break in elevation of 19 in or more, unless a ramp, runway or hoist is provided | 1926.1051(a) |
Duty ratings
| Type | Duty | Rated load |
|---|---|---|
| IAA | Special duty | 375 lb |
| IA | Extra heavy duty | 300 lb |
| I | Heavy duty | 250 lb |
| II | Medium duty | 225 lb |
| III | Light duty | 200 lb |
Pick a ladder rated for you plus your tools and materials. A 200 lb roofer carrying a 60 lb bundle of shingles is at 260 lb before boots and tool belt, which is beyond a Type I ladder’s 250 lb.
Common mistakes
- Resting the ladder on gutters, which bend, instead of the wall or a stand-off.
- Feet on soft ground, loose gravel or a sloping drive without levellers or a tie-off.
- Overreaching: keep your belt buckle between the rails and move the ladder.
- Aluminium ladders near overhead power lines: keep well clear, and use fibreglass for electrical work.
- Extension ladders set too short, so the top rungs are used as steps.
Frequently asked questions
What is the 4 to 1 ladder rule?
For every 4 ft of ladder working length (feet to top support), set the base 1 ft away from the wall. It puts the ladder at about 75.5° and is the OSHA requirement for ladders that are not self-supporting (29 CFR 1926.1053(b)(5)(i)).
What angle should a ladder be at?
About 75 degrees from the ground (75.5° exactly for the 4-to-1 ratio).
How far should a ladder extend above a roof?
At least 3 ft above the roof edge or landing when you use it to get onto the roof, or the top must be secured to a rigid support with a grab rail (1926.1053(b)(1)).
What size ladder do I need for a 10 ft roof?
At least 13.4 ft of ladder at the correct angle, so a 14 ft straight ladder, or an extension ladder with a maximum working length of 14 ft or more.
How far apart are ladder rungs?
10 to 14 in centre to centre under OSHA rules (1926.1053(a)(3)(i)); most ladders are about 12 in.
Sources
- 29 CFR 1926.1053, Ladders; 29 CFR 1926.1051, General requirements (stairways and ladders); 29 CFR 1910.23, Ladders (general industry, scope only). US federal regulations, read at law.cornell.edu (text cached 24 October 2026).
- ANSI A14 ladder standards: duty classes and ratings as marked on ladder labels (names and ratings only).
Last reviewed: 24 October 2026. Numbers in the tables are our arithmetic from the sources listed; code sections are summarised, not quoted. How we check our work: methodology and corrections. Spotted an error? Please let us know.