Most ladder accidents are not caused by a broken ladder. They happen because the ladder was set up badly. If the foot is too close to the wall, the ladder can tip backwards. If it is too far out, the foot can slide away. The right angle is not hard to find, and this calculator does the sum for you.
Enter the height you need to reach, and the calculator will tell you how far to place the ladder from the wall.
What is the 4 to 1 rule?
The 4 to 1 rule is the simplest way to get a safe ladder angle. For every 4 units of height that the ladder reaches up the wall, the foot of the ladder should be 1 unit away from the wall. So if the top of the ladder touches the wall at 4 metres, the foot should be 1 metre out.
This gives an angle of about 75 degrees from the ground, which is steep enough to avoid slipping and shallow enough to avoid tipping.
The ladder angle formula
Distance from the wall = Height reached / 4
To find the length of ladder needed to touch the wall at that height, you can use the right-angle triangle rule:
Ladder length = square root of (Height squared + Distance squared)
Worked example
A worker needs to reach a roof edge 4.8 metres above the ground.
- Distance from the wall = 4.8 / 4 = 1.2 m
- Ladder length to touch the wall at 4.8 m = square root of (4.8 x 4.8 + 1.2 x 1.2) = about 4.95 m
The ladder must also stick out about 1 metre above the roof edge, so the worker has something to hold when stepping on and off. That means the ladder needs to be about 6 metres long, not 5.
Another quick case: to reach 3 metres, the foot should be 0.75 m from the wall, and the ladder should be at least 3.1 m long.
A quick check without a tape
Here is a trick that works on site. Stand with your toes at the foot of the ladder and hold your arms straight out in front of you. Your palms should just reach the rung at shoulder height. If you have to lean forward, the ladder is too upright. If your arms are bent, the ladder is too flat. This is only a rough check, so use the calculation when you can.
Before you climb: a short checklist
- Is a ladder the right tool? A ladder is for short, light, low-risk jobs. For long or heavy work, use a platform, scaffold or tower.
- Check the ladder: look for bent rails, cracks, missing or loose rungs, damaged feet and a clear inspection tag.
- Level, firm ground: never put the foot on loose bricks, boxes or soft ground.
- Secure it: tie the top, or get someone to foot the base, so it cannot slide.
- Extend it: the ladder should rise about 1 metre above the landing point.
- Keep three points of contact: two hands and one foot, or two feet and one hand, all the time.
- Do not overreach: keep your belt buckle between the rails, and move the ladder instead of leaning out.
- Stay away from live power: use non-conductive ladders for electrical work, and keep well clear of overhead lines.
Step by step
- Measure the height of the point where the ladder will touch the wall or edge.
- Enter that height in the calculator.
- Read the distance for the foot of the ladder.
- Choose a ladder that is long enough, and which rises about 1 metre above the landing.
- Place the foot at the correct distance on firm, level ground.
- Secure the ladder before anyone climbs.
What goes wrong with the wrong angle
- Too steep: the climber’s weight can pull the top away from the wall, and the ladder can fall backwards. This is a real danger on tall ladders and when carrying loads.
- Too shallow: the foot can kick out from under the climber, and the ladder slides down the wall. The rungs also become harder to climb safely.
Common mistakes
- Setting the ladder by eye, which usually gives an angle that is too flat
- Measuring from the top of the ladder instead of the point where it touches the wall
- Forgetting that the ladder must go about 1 metre above the landing
- Using the top rungs, which are not meant to be stood on
- Putting the ladder in front of a door that may open
- Carrying heavy or bulky items up the ladder
- Leaving a ladder unsecured “just for a minute”
Linking it to your wider plan
Work at height is one of the main causes of serious injury and death. Score the task with the risk matrix calculator, since a fall can easily reach the highest severity level. When a fall arrest harness is used, the fall clearance calculator shows how much free space you need below the anchor point.
Frequently asked questions
What is the safe angle for a ladder?
About 75 degrees from the ground. The 4 to 1 rule gives you this angle.
How far from the wall should a 6 metre ladder be?
It depends on the height that the ladder reaches. If the ladder touches the wall at 4.8 metres, the foot should be 1.2 metres out.
How far above the roof should a ladder extend?
About 1 metre above the landing point, so that there is something to hold when you step on or off.
Does the 4 to 1 rule work for step ladders?
No. A step ladder is free-standing and should be fully opened and locked. The 4 to 1 rule is for leaning ladders.
Is a ladder safe for long jobs?
Not usually. For long or heavy work, a platform or scaffold is a safer choice.
Learn this properly
Work at height and ladder safety are covered in NEBOSH, IOSH and OSHA courses. ISH Institutes teaches these in Peshawar. Chat with us on WhatsApp and we will help you pick the right course.