About the Ladder Calculator
Ladder Calculator helps you set up a leaning ladder safely. Enter the height where the ladder will rest and it tells you how far from the wall to place the foot (one quarter of the height, the 4-to-1 rule), the safe angle of about 76 degrees and the shortest ladder that can reach, plus how much longer it must be if it should stick out above the landing. Or enter the length of the ladder you already have and the distance of its foot from the wall, and the page tells you the angle, the height it reaches and whether the angle is safe. Use feet or metres.
Updated October 2026
How to use the Ladder Calculator
- 1Choose feet or metres.
- 2To plan, enter the height where the ladder will rest.
- 3Read the foot distance, the angle and the ladder length.
- 4To check a ladder you have, enter its length and the foot distance.
- 5See whether the angle is safe and how high it reaches.
Why the angle matters
A ladder stays up by friction at its foot and the support at its top. If it is too shallow, the foot can slide out. If it is too steep, it can fall backwards and the climber's weight pulls the top away from the wall. The 4-to-1 rule gives an angle near 75 degrees, where both risks are low.
Setting up in steps
Find the height where the ladder will rest, divide it by four for the foot distance and check that the ladder is long enough, with at least three rungs above the top if you will step off. Check that the feet are on solid ground and tie or hold the top if you can.
- Divide the height by 4 to find the foot distance
- Make sure the ladder reaches 3 rungs (about 1 m) higher
- Face the ladder and keep three points of contact
- Do not overreach: move the ladder instead
Safety checks
Inspect the ladder before every use for cracks, loose rungs and damaged feet. Keep away from power lines and never use a metal ladder near electricity. If the work is high or long, consider a scaffold or a platform ladder, and ask someone to foot the ladder.
Related tools
Work out roof slopes with the Roof Pitch Calculator, find triangle sides with the Pythagorean Theorem Calculator, plan stairs with the Stair Calculator and convert lengths with the Length Converter. The Roofing Calculator estimates materials.
Features
- 4-to-1 rule and safe angle
- Ladder length for a height
- Check the angle of a ladder you already have
- Allowance for extending above the landing
- Feet or metres
- Private: nothing is uploaded
Frequently asked questions
What is the 4-to-1 rule for ladders?
For every 4 units of height to the point where the ladder touches the wall, the foot should be 1 unit from the wall. That puts the ladder at about 75 degrees.
What angle is safe?
About 75 degrees. Below about 70 the ladder can slide and above about 80 it can tip backwards.
How far above the roof or landing should the ladder reach?
At least three rungs, or about one metre (three feet), so that you can step on and off safely and have something to hold.
How long a ladder do I need for a 12 foot height?
The ladder must be at least 12.4 feet long to lean at 12 feet, and you need about 15.5 feet if it should reach three feet above. Choose the next standard size up.
How do I set up a ladder on uneven ground?
Use a ladder leveller or stabiliser made for the job, never bricks or boxes. Make sure that the feet are on firm, level ground.
Does the ladder's weight rating matter?
Yes. Add your own weight, your clothing and your tools, and stay below the duty rating on the ladder.
Can I use the ladder on a slippery or windy day?
No. Wet, icy or windy conditions make ladders much more dangerous.
Is this a safety guarantee?
No. It is a geometry helper. Always read the ladder's label, check the ladder and follow your local rules.