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Home improvement

Ladder Angle Calculator

Ladder angle against the 4:1 rule, and the length you need.

Your measurementsEvery assumption editable01

Where the ladder touches the wall or the edge of the roof.

Three feet is the usual requirement where you step off at the top.

Ladder setupCalculated live02

Result

76degrees

Within the 4:1 working range

Height to contact
16 ft
Base distance
4 ft
Ratio4:1 is the target
4 : 1
Angle to the groundabout 75.5° at 4:1
75.96°
Ideal base distancea quarter of the working height
4 ft
Ladder length to contact
16.492 ft
Total ladder neededincluding 3 ft above the landing
19.49 ft
Assessment
Within the 4:1 working range

The four-to-one rule is one foot of base for every four feet of working height, which puts the ladder at about 75.5 degrees. Shallower and the base tends to slide out from under you; steeper and it can tip backwards as you climb.

Where you step off at the top, the ladder should extend about three feet above the landing so there is something to hold while transitioning. That extension is above the contact point, so the ladder has to be longer than the height alone suggests.

A ladder's rated length is its overall length, and the usable height is always less once the angle and the overlap between sections are accounted for. Buy longer than the arithmetic suggests.

One foot of base for every four feet of working height, which puts the ladder at about 75.5°. Shallower and the base slides out; steeper and it tips backwards. This checks your setup and works out the length to buy.

Why use this tool?What it does differently03

Why use this tool?

Assessed, not just measured

States whether the setup is too shallow, too steep or within the working range.

Ideal base distance

A quarter of the working height, so you can correct rather than guess.

Length to buy

Including the three feet above the landing you need to hold while stepping off.

Rated versus usable

A ladder's rated length is not its usable height once angle and section overlap are counted.

How this worksThe method04

How this ladder angle calculator works

The angle is the arctangent of height over base distance. At the 4:1 ratio that comes out at about 75.5 degrees, which is the setup angle every ladder standard converges on.

Too shallow and the horizontal force at the base exceeds what friction can hold, so it slides out. Too steep and the centre of gravity moves behind the rails as you climb, so it tips backwards. The acceptable window is narrower than it feels.

Where you step off at the top, the ladder should extend about three feet above the landing so there is something to hold during the transition. That extension is measured above the contact point, so the ladder must be longer than the height alone implies.

How to use itStep by step05

How to use it

  1. Step 1: Measure the height

    To the point where the ladder touches the wall or roof edge.

  2. Step 2: Set the base

    A quarter of that height out from the wall.

  3. Step 3: Check the assessment

    Adjust the base until it falls in the working range.

  4. Step 4: Add the landing extension

    Three feet above where you step off, if you are stepping off at all.

Example usageWorked figures06

Example usage

A correct setup
16 ft to the contact point with the base 4 ft out is exactly 4:1 — 75.96°, comfortably in range. The ladder to the contact point is 16.49 ft, so with 3 ft above the landing you need about 19.5 ft.
Too shallow
The same 16 ft height with the base 6 ft out drops to 69.4° and a 2.7:1 ratio. That is the classic slide-out setup.
Too steep
Base at 2.5 ft gives 81.1° and 6.4:1. It feels secure until your weight moves the centre of gravity behind the rails near the top.
Frequently asked questionsCommon questions07

Frequently asked questions

What is the 4 to 1 ladder rule?

One foot of base distance for every four feet of working height, which sets the ladder at about 75.5 degrees. It is the setup angle every major ladder standard converges on.

What angle should a ladder be at?

About 75.5 degrees from the ground. Meaningfully shallower risks the base sliding out; meaningfully steeper risks tipping backwards as you climb.

How far above the roof should a ladder extend?

About three feet above the landing point, so there is something to hold while stepping on and off. That is the most dangerous moment of any ladder use.

What size ladder do I need?

Longer than the straight-line distance to the contact point, plus the landing extension. A 16 ft working height at 4:1 needs roughly a 19 to 20 ft ladder.

Why is rated length more than usable height?

Because the ladder leans rather than standing vertical, and extension ladders lose length to the overlap between sections. Both mean usable height is always less than the rating.

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