The 4-to-1 Rule for Ladder Safety
The most important rule for using an extension ladder safely is the "4-to-1 Rule". This OSHA-recommended rule states that for every four feet of height you need to climb, the base of the ladder should be moved one foot away from the wall.
Following this rule creates a stable working angle of approximately 75.5 degrees. This calculator helps you verify that angle instantly. A ladder that is too steep can tip over backward, while a ladder that is too shallow can slide out from the bottom.
4-to-1 Rule Quick Reference
| If Ladder Touches Wall at: | Base Should be This Far Out: |
|---|---|
| 8 ft | 2 ft |
| 12 ft | 3 ft |
| 16 ft | 4 ft |
| 20 ft | 5 ft |
| 24 ft | 6 ft |
How to Use the Calculator
- Set up your ladder on firm, level ground.
- Measure the vertical distance from the ground to the point where the ladder touches the wall.
- Measure the horizontal distance from the base of the wall to the base of the ladder's feet.
- Enter both values into the calculator and click "Check Angle" to see your safety status.
Frequently Asked Questions
Does this apply to all ladders?
No. This calculator and the 4-to-1 rule are specifically for single and extension ladders. They do not apply to stepladders or A-frame ladders, which should always be fully opened with their spreaders locked.
What if the ground is not level?
Never set up a ladder on uneven ground. Use a dedicated ladder leveling tool or dig out the high side to create a level, stable base. Do not use bricks or blocks to prop up one side, as they can easily slip.