Ladder Angle Calculator
Set a leaning ladder at a safe angle. Enter the ladder length and how far the base sits from the wall, and get the angle, the height it reaches up the wall, and a safety check against the 4:1 rule (about 75.5°) — plus the recommended base distance, how far to move the feet, an optional roof-edge 3-ft extension check, by-base and by-length tables, and a downloadable PDF.
| Base | Angle | Vertical reach | vs target |
|---|---|---|---|
| Enter a ladder to compare | |||
| Length | Base (4:1) | Vertical reach | Highest standing |
|---|---|---|---|
| Enter a ladder to compare | |||
How to use the ladder angle calculator
Four quick steps turn your ladder length and base distance into the ladder angle, how high it reaches and whether it meets the 4:1 safety rule — with by-base and by-length tables and a downloadable report.
Enter the ladder
Give the ladder length to the top support point and how far the feet sit out from the wall.
Add a roof edge
Optionally enter the gutter or roof height to check the 3 ft extension above it.
Pick a target angle
Choose 75.5° for the 4:1 rule, or a slightly shallower or steeper target.
Read results & save a PDF
Get the angle, reach and where to move the base, compare setups — then download a report.
How the ladder angle is calculated
The ladder, wall and ground form a right triangle, so the angle and reach come straight from the ladder length and base distance. Here is the exact math the calculator runs.
Worked example — 24 ft ladder, base 6 ft from the wall, 75.5° target
Angle: arccos(6 ÷ 24) ≈ 75.5° · Ratio: 24 ÷ 6 = 4 : 1
Reach: √(24² − 6²) ≈ 23.2 ft · Recommended base: 24 × cos(75.5°) ≈ 6.0 ft
Standing height: 23.2 − 3 ≈ 20.2 ft · Roof check (20 ft edge): 23.2 − 20 ≈ 3.2 ft above
≈ 75.5° — a good 4:1 setup reaching about 23.2 ft, safe to step onto a roof up to about 20 ft high.
Ladder angle reference charts
Handy lookups for how base distance changes the angle, where to set the base for common ladder lengths, and the base for each target angle.
| Base | Angle | Vertical reach | vs 75.5° target |
|---|---|---|---|
| 3 ft | 82.8° | 23.8 ft | Too steep |
| 4 ft | 80.4° | 23.7 ft | Too steep |
| 5 ft | 78.0° | 23.5 ft | Too steep |
| 6 ft | 75.5° | 23.2 ft | OK |
| 7 ft | 73.0° | 23.0 ft | Too shallow |
| 8 ft | 70.5° | 22.6 ft | Too shallow |
OK means within 2° of the target. Each foot of base changes the angle by about 2.5° on a 24 ft ladder.
| Ladder length | Base (4:1) | Vertical reach | Highest standing |
|---|---|---|---|
| 16 ft | 4 ft | 15.5 ft | 12.5 ft |
| 20 ft | 5 ft | 19.4 ft | 16.4 ft |
| 24 ft | 6 ft | 23.2 ft | 20.2 ft |
| 28 ft | 7 ft | 27.1 ft | 24.1 ft |
| 32 ft | 8 ft | 31.0 ft | 28.0 ft |
| 40 ft | 10 ft | 38.7 ft | 35.7 ft |
Length is measured to the top support point. Extension ladders lose some length to section overlap.
| Target | Base | Notes |
|---|---|---|
| 73° | 7.02 ft | Shallower — more slide-out risk |
| 75.5° | 6.01 ft | 4:1 rule (OSHA/ANSI) |
| 77° | 5.40 ft | Steeper — more tip-back risk |
Base = length × cos(angle). Always set up on firm, level ground.
Everything the calculator works out
A ladder length and a base distance give you the full setup picture — angle, reach, a safety check and exactly how far to move the feet.
Key figures behind the estimate
Built for anyone climbing a ladder
From cleaning gutters to painting a second story, the same calculator tells you whether your ladder is set up safely.
Cleaning gutters or fixing trim and wants to know where to set the ladder feet and whether it reaches.
- Enter ladder length
- Set base to length ÷ 4
- Check the reach
Moving ladders around a job all day and wants a fast check on angle and standing height.
- Compare base distances
- Read standing height
- Save a PDF for crews
Shopping for an extension ladder and needs one long enough to clear the roof edge by 3 ft.
- Enter the roof height
- Try different lengths
- Allow for section overlap
7 things to know about ladder safety
A correct angle is only part of a safe setup — these habits keep the ladder, and you, steady.
Ladder angle calculator FAQ
The angle, reach and setup questions people ask most about using a leaning ladder safely.
The recommended angle for a leaning ladder is about 75.5 degrees from the ground. That is the angle you get by following the 4-to-1 rule, and it is the setup recommended by OSHA and ANSI ladder safety standards for portable extension and straight ladders.
At this angle the ladder is steep enough that the feet are unlikely to slide out, but not so upright that it can tip backward when you climb or lean. This calculator treats anything within 2 degrees of your target as a good setup.
Step ladders are different: they are designed to be used fully opened and locked, not leaned against a wall, so this angle applies only to leaning ladders.
The 4-to-1 rule says the base of the ladder should be 1 foot out from the wall for every 4 feet of ladder length up to the point where it rests. A 20-foot ladder goes 5 feet out, a 24-foot ladder 6 feet out, and a 32-foot ladder 8 feet out.
Following the rule sets the ladder at about 75.5 degrees, which is why it is the most widely used ladder safety guideline.
Measure the length along the rails from the feet to the top support point, not the total length of the ladder if part of it extends above the wall or roof edge.
The ladder, the wall and the ground form a right triangle. The angle at the ground equals the arccosine of the base distance divided by the ladder length: angle = arccos(base ÷ length).
For a 24-foot ladder with its feet 6 feet from the wall, that is arccos(6 ÷ 24), or about 75.5 degrees. Moving the base to 8 feet drops the angle to about 70.5 degrees, and moving it in to 4 feet raises it to about 80.4 degrees.
To find where to put the base for a target angle, work it backward: base = length × cos(angle). For 75.5 degrees on a 24-foot ladder, that is about 6 feet.
The vertical reach is the height of the triangle: reach = the square root of (length² − base²). A 24-foot ladder set 6 feet out reaches about 23.2 feet up the wall.
Set at the 4-to-1 angle, a 16-foot ladder reaches about 15.5 feet, a 20-foot ladder about 19.4 feet, a 28-foot ladder about 27.1 feet, and a 32-foot ladder about 31 feet.
For extension ladders, the sections overlap, so the usable length is shorter than the size printed on the label. Measure the extended length to the top support point for an accurate figure.
To step on and off a roof safely, the ladder should extend about 3 feet above the roof edge so you have something to hold onto during the transition. That means the vertical reach needs to be at least the edge height plus 3 feet.
For example, a 24-foot ladder at the 4-to-1 angle reaches about 23.2 feet, so it extends about 3.2 feet above a 20-foot roof edge, which is enough. For a 21-foot edge, it would extend only about 2.2 feet, so you would need a longer ladder.
Enter the roof or gutter height in the calculator and it checks whether your ladder reaches the edge and clears it by 3 feet.
If the angle is too shallow, meaning the base is too far from the wall, the feet are more likely to slide out from under you as you climb. If it is too steep, with the base too close to the wall, the ladder can tip backward, especially when you lean out or reach overhead.
For a 24-foot ladder, a base 8 feet out gives about 70.5 degrees, which is too shallow, so the base should move in about 2 feet. A base 4 feet out gives about 80.4 degrees, which is too steep, so it should move out about 2 feet.
The calculator shows how far to move the base, and in which direction, to reach your target angle.
As a planning guide, this calculator puts the highest safe standing height about 3 feet below the top support point, so you can keep your hands on the rails and your body inside them. A 24-foot ladder set at 75.5 degrees reaches about 23.2 feet, giving a standing height of about 20.2 feet.
Always follow the ladder’s own labels, which mark the highest standing level, and never stand on the top rungs or the top cap of a ladder.
Keep three points of contact while climbing, keep your belt buckle between the rails, and move the ladder rather than overreaching to the side.
Yes. A common field check is to stand with your toes touching the feet of the ladder and stretch your arms straight out in front of you. If your palms rest on a rung at shoulder height, the angle is close to correct.
Many extension ladders also have an angle indicator label on the side rail that shows when the ladder is set at about 75 degrees.
For a precise setup, measure the ladder length to the top support and set the base at one quarter of that distance, or enter both numbers in this calculator.
Planning aid only — follow your ladder’s labels. This calculator works in US units (feet): angle = arccos(base ÷ length), vertical reach = √(length² − base²), and the recommended base = length × cos(target angle). The 4:1 rule (base out 1 ft for every 4 ft of length) gives about 75.5°, the OSHA and ANSI target for a leaning ladder; setups within 2° of the target are shown as good. The roof check looks for about 3 ft of ladder above the edge, and the standing height is the reach minus 3 ft. Set the ladder on firm, level ground, secure the top or have the base footed, keep three points of contact, stay clear of power lines, and follow the ladder maker’s duty rating and instructions and any local rules. For planning purposes only.