Ladder Angle Calculator checks a leaning ladder against OSHA's 75.5° 4:1 rule from your height and base distance, then shows where to set the foot and which extension ladder works.
Height runs from the ground to where the rails touch the wall or roof edge.
Ladder Use and Weight
Extension Ladder Size Chart
| Ladder | Max Working | Roof Edge Up To | Foot Out | Max Reach |
|---|---|---|---|---|
| 16 ft | 13.0 ft | 9.7 ft | 2 ft 6 in | 15.3 ft |
| 20 ft | 17.0 ft | 13.6 ft | 3 ft 6 in | 19.2 ft |
| 24 ft | 21.0 ft | 17.4 ft | 4 ft 6 in | 23.0 ft |
| 28 ft | 25.0 ft | 21.3 ft | 5 ft 6 in | 26.9 ft |
| 32 ft | 29.0 ft | 25.2 ft | 6 ft 6 in | 30.8 ft |
| 36 ft | 32.0 ft | 28.1 ft | 7 ft 3 in | 33.7 ft |
| 40 ft | 35.0 ft | 31.0 ft | 8 ft | 36.6 ft |
| 44 ft | 39.0 ft | 34.9 ft | 9 ft | 40.5 ft |
| 48 ft | 43.0 ft | 38.7 ft | 10 ft | 44.3 ft |
Foot Position vs Angle
| Rise to Run | Foot Out | Angle | Friction Needed |
|---|---|---|---|
| 2.75 : 1 | 5 ft 5-1/2 in | 70.0° | 0.36 |
| 3.00 : 1 | 5 ft | 71.6° | 0.33 |
| 3.50 : 1 | 4 ft 3-3/8 in | 74.1° | 0.29 |
| 3.87 : 1 (OSHA) | 3 ft 10-1/2 in | 75.5° | 0.26 |
| 4.00 : 1 (1 per 4 up) | 3 ft 9 in | 76.0° | 0.25 |
| 4.50 : 1 | 3 ft 4 in | 77.5° | 0.22 |
| 5.00 : 1 | 3 ft | 78.7° | 0.20 |
| 5.67 : 1 | 2 ft 7-3/4 in | 80.0° | 0.18 |
Set Your Lean With the Ladder Angle Calculator
The Ladder Angle Calculator turns two tape measurements into the angle of a leaning ladder. It then shows where OSHA's 4:1 rule puts the foot, which extension ladder reaches the job, and how hard the feet have to grip.
Roofers, gutter cleaners, painters and siding crews use it before they climb. Safety leads use it to check a setup against OSHA, and homeowners use it to buy the right ladder the first time.
Five Ways Into the Ladder Angle Calculator
Height + Base Distance checks a ladder that is already standing. Height Only tells you which extension ladder to buy, and Ladder Size shows how high a given ladder reaches at the correct angle.
The last two modes pair a ladder length with the height or the base. Ladder length here runs along the rails from the feet to the top support, not the size on the label.
Lengths work in feet or meters, and weight in pounds or kilograms. The Ladder Use and Weight panel sets roof access or wall only, plus the weight of the climber and tools.
Where H, B and L Are Measured
Height H runs from the ground to the point where the rails rest on the wall or roof edge. Base B is the level distance out to the feet. Working length L is the stretch of ladder between those two points.
OSHA Measures 4:1 Along the Ladder
The angle itself is plain right-triangle math. With H as the height to the top support and B as the distance out to the foot, the angle from the ground comes from the inverse tangent.
The Angle of Depression Calculator runs the same inverse tangent on a sight line. For a ladder, OSHA 1926.1053(b)(5)(i) sets the target angle. The horizontal distance from the top support to the foot must be about one-quarter of the working length, measured along the ladder.
That works out to 75.5° from the ground, or 14.5° off the wall. Many guides teach one foot out for every four feet up instead. That version divides the height by four, so the tangent becomes exactly 4 and the angle lands at 76.0°.
The gap is small but real. At 15 ft of height, the OSHA foot spot is 3 ft 10-1/2 in out, while the height version gives 3 ft 9 in. The Ladder Angle Calculator uses the OSHA version and shows both rows in its Foot Position vs Angle table.
A common slip is typing the ladder's label size into the Ladder Length field. A 24 ft extension ladder never has 24 ft of working length, because its sections overlap and the rails may run past the roof edge.
One case changes the target completely. OSHA 1926.1053(b)(5)(ii) sets job-made wood ladders with spliced side rails at one-eighth of the working length. That is about 82.8°, far steeper than a factory extension ladder.
Reading the Angle and the Foot Move
The top result shows the measured angle and a verdict. Within 1° of 75.5° reads as on the 4:1 rule. Up to 5° off reads as slightly flat or slightly steep, and anything past that reads as too flat or too steep.
The first card turns the verdict into a tape measurement. At the default 15 ft height and 4 ft base, the ladder sits at 75.1°, and moving the foot in 1-1/2 in puts it on 75.5°.
The card also shows your rise to run, 3.75 to 1 here. Rise to run is the same idea used to lay out the Stair Calculator and the Ramp Calculator, but a ladder runs far steeper than either.
Distances must be above zero and up to 150 ft, about 45.7 m. The angle must fall between 30° and 89.5°, and a ladder length must be longer than the height or base paired with it. Near 90° the tangent heads toward infinity and the foot distance shrinks to almost nothing.
Extension Ladder Size for Roof Access
Roof access adds a second OSHA rule. Under 1926.1053(b)(1), the side rails must extend at least 3 ft above the upper landing. If the ladder is too short for that, the top has to be secured to a rigid support and a grab rail added.
So the Ladder Angle Calculator first finds the working length at 75.5° for your height. It then adds the 3 ft of rail that has to stand above the edge.
Next it subtracts the section overlap from each ladder size. ANSI A14.2 for metal ladders and the Cal/OSHA ladder rules call for about 3 ft of overlap up to 32 ft, 4 ft from there to 36 ft, and 5 ft from 36 to 48 ft.
Here S is the ladder size and O is the overlap. The smallest ladder whose max working length covers the need is the pick. For a 15 ft roof edge the need is 18.5 ft, a 20 ft ladder only works to 17 ft, so the result is a 24 ft ladder extended to 18.5 ft.
Werner's sizing advice lands in the same place, with an extension ladder 7 to 10 ft longer than the support point. The overlap stops on your own ladder still have the final word.
The size chart runs from 16 to 48 ft and shows the roof edge or wall contact each size serves. Cal/OSHA caps two-section metal ladders at 48 ft, so past that the calculator points to a lift or scaffold.
Highest Standing Rung and Reach
Werner puts the highest standing level of an extension ladder four rungs down from the top. The calculator takes about 4 ft off the extended rails and converts what is left to a height at the set angle.
Overhead reach adds a 5 ft 7 in person with a 12 in reach, the same person used in Werner's ladder height chart. A fully extended 24 ft ladder gives about 23 ft of reach, which matches Werner's published figure.
At a 15 ft roof edge, the highest standing rung sits at about 14 ft. That keeps you below the roof line, where Werner says you should never stand above.
Why a Flat Ladder Kicks Out at the Foot
The fourth card estimates the sideways push at the feet for a worst case. It puts the full weight at the top support on a slick wall with no friction, and it leaves out the ladder's own weight.
Taking moments about the foot gives the push in terms of the climber weight W. The wall presses on the top with the same force the ground has to hold at the base.
The friction the feet need is the same ratio without the weight. If the ground and the ladder shoes grip less than this, the base can slide out.
At 75.5° the feet need a friction coefficient of about 0.26. At 70° that rises to 0.36, about 41% more grip for the same climber. With 250 lb at the top of the default setup, the push comes to about 67 lb.
The weight you enter is not a capacity check. The duty rating must cover you, your clothes, tools and materials, and OSHA 1926.1053(a)(3) bars loading past it. Werner rates Type I ladders at 250 lb and Type IA at 300 lb.
Real-world safety also depends on firm ground, the condition of the ladder shoes and whether the top is tied off. Treat the angle as one check in the setup, not the whole safety review.
Measurements That Skew the Result
Measuring height to the top of the rails instead of the contact point is the most common error. The 3 ft of rail past the roof edge is not part of H.
The base distance starts from a point straight below the top support. OSHA's wording runs from the top support to the foot, so when the rails rest on a gutter that sticks out from the wall, measure from under the gutter rather than from the foundation.
A phone or angle finder must read the angle from the ground. A reading of 14.5° off the wall is the same setup as 75.5° from the ground, and mixing the two flips the verdict.
What Climbers Ask About Ladder Angle
What angle should an extension ladder be set at?
Set it at 75.5° from the ground, which is 14.5° off the wall. That is the angle OSHA's one-quarter rule produces, and it is why most guides round the answer to 75°.
OSHA writes the rule as a distance, not a degree figure. At 24 ft of height, the one-quarter rule puts the foot about 6 ft 2-3/8 in out, while dividing the height by four gives 6 ft even.
What size extension ladder do I need for a two-story house?
Measure from the ground to the roof edge where the ladder will rest. At 75.5° with 3 ft of rail above the edge, a 24 ft ladder serves a roof edge up to about 17.4 ft, and a 28 ft ladder serves one up to about 21.3 ft.
Roofing suppliers usually point two-story homes to a 24 or 28 ft ladder, and your measured height decides which. A 32 ft ladder covers a roof edge up to about 25.2 ft.
How can I check the ladder angle without a tape measure?
Stand with your toes against the feet of the ladder and hold your arms straight out in front of you. At about the right angle, your palms land on a rung near shoulder height, a check that OSHA training material describes.
It is a quick field check rather than a measurement. Arm length varies from person to person, so confirm the foot distance with a tape on any tall setup, or run the numbers through the Ladder Angle Calculator.
Does the 4-to-1 rule apply to a step ladder?
No. A step ladder is self-supporting, and OSHA's one-quarter rule covers non-self-supporting ladders only. A step ladder belongs fully open with its spreaders locked, never folded and leaned against a wall.
Using a step ladder as a straight ladder breaks OSHA 1926.1053(b)(4), which limits ladders to their designed use. Werner puts its highest standing level two steps down from the top.