What Size Extension Ladder Do I Need? Height and Reach Chart
Part of the project planner: Planning a roof replacement.
To reach a roof edge 18 ft up you need a 28 ft extension ladder, set 4.6 ft from the wall. The ladder has to run from the ground to the roof edge at the safe angle and then extend 3 ft above it, and an extension ladder works about 3 ft shorter than its label because the sections overlap. The ladder length calculator does the math for your own height, or tells you how high the ladder you own will reach.
Ladder size for each height
Stepping from the ladder onto a roof, which means the ladder extends 3 ft above the edge:
| Roof edge or gutter height | Extension ladder size | Set the base this far out |
|---|---|---|
| 8 ft | 16 ft | 2.1 ft (25 in) |
| 10 ft | 20 ft | 2.6 ft (31 in) |
| 12 ft | 20 ft | 3.1 ft (37 in) |
| 14 ft | 24 ft | 3.6 ft (43 in) |
| 16 ft | 24 ft | 4.1 ft (50 in) |
| 18 ft | 28 ft | 4.6 ft (56 in) |
| 20 ft | 28 ft | 5.2 ft (62 in) |
| 22 ft | 32 ft | 5.7 ft (68 in) |
| 24 ft | 32 ft | 6.2 ft (74 in) |
| 26 ft | 36 ft | 6.7 ft (81 in) |
Working against a wall, such as painting or fixing a gutter, with no landing:
| Height of the top of the ladder | Extension ladder size | Set the base this far out |
|---|---|---|
| 8 ft | 16 ft | 2.1 ft (25 in) |
| 10 ft | 16 ft | 2.6 ft (31 in) |
| 12 ft | 16 ft | 3.1 ft (37 in) |
| 14 ft | 20 ft | 3.6 ft (43 in) |
| 16 ft | 20 ft | 4.1 ft (50 in) |
| 18 ft | 24 ft | 4.6 ft (56 in) |
| 20 ft | 24 ft | 5.2 ft (62 in) |
| 22 ft | 28 ft | 5.7 ft (68 in) |
| 24 ft | 28 ft | 6.2 ft (74 in) |
| 26 ft | 32 ft | 6.7 ft (81 in) |
How high a ladder reaches
| Ladder size | Working length | Reaches a roof edge | Reaches a wall |
|---|---|---|---|
| 16 ft | 13 ft | 9.7 ft | 12.6 ft |
| 20 ft | 17 ft | 13.6 ft | 16.5 ft |
| 24 ft | 21 ft | 17.4 ft | 20.3 ft |
| 28 ft | 25 ft | 21.3 ft | 24.2 ft |
| 32 ft | 29 ft | 25.2 ft | 28.1 ft |
| 36 ft | 33 ft | 29.0 ft | 32.0 ft |
| 40 ft | 36 ft | 32.0 ft | 34.9 ft |
| 44 ft | 40 ft | 35.8 ft | 38.7 ft |
| 48 ft | 44 ft | 39.7 ft | 42.6 ft |
For example, a 32 ft ladder works 29 ft and reaches a roof edge 25.2 ft up. These are the highest points where the ladder can rest. You never stand at the top of the ladder, so the height you can work at is lower.
The rules of safe setup
- The 4 to 1 rule. The base goes one foot out for every four feet of ladder up to the support point. Too upright and the ladder can tip back; too shallow and the foot can slide.
- Extend 3 feet above a roof. The rails give you something to hold as you step on and off.
- The overlap. The two sections of an extension ladder overlap by 3 ft (up to 36 ft), 4 ft (up to 48 ft) or 5 ft above that, so the size on the label is longer than the ladder works.
- Firm, level ground. Level the feet with a ladder leveler on a slope, never with blocks or bricks.
- Tie it off. Secure the top, and use a stabilizer or stand-off so that the ladder does not rest on a gutter.
- Three points of contact, and never stand above the fourth rung from the top.
- Keep 10 feet from overhead power lines, and choose a fiberglass ladder near any electrical work.
Choosing the ladder
- Duty rating. Ladders are rated for the weight of you plus tools and materials: type IAA 375 lb, IA 300 lb, I 250 lb, II 225 lb and III 200 lb. Pick one that covers your weight plus what you carry.
- Material. Fiberglass does not conduct electricity and is the safe choice near wires. Aluminum is lighter and cheaper but conducts.
- Weight. A 28 ft fiberglass ladder is heavy: think about who will carry it and whether you can raise it safely.
- A step ladder is not a lean-to ladder. Never lean a step ladder against a wall, and never use the top step.
If the job needs more than about a 40 ft ladder, or a roof with a steep pitch, hire a pro or a lift. See the roof pitch calculator for the slope of a roof, and the roofing calculator if you are re-roofing. Follow the ladder label, the manufacturer's instructions and your local rules.
Frequently asked questions
What size ladder do I need to reach a roof?
Measure the height of the roof edge and add 3 ft for the part of the ladder above it. A roof edge 18 ft up needs 21.6 ft of working ladder, so a 28 ft extension ladder. A 20 ft edge needs a 28 ft ladder.
How high will a 24 ft extension ladder reach?
About 17 ft to a roof edge you step onto, or 20 ft to a wall. Its working length is 21 ft, since the sections overlap by 3 ft.
How high will a 28 ft extension ladder reach?
About 21 ft to a roof edge, or 24 ft against a wall. It is the usual size for the gutter of a two-story house.
What is the 4 to 1 rule for ladders?
Set the foot of the ladder one foot out from the wall for every four feet of ladder to the support point. For a ladder reaching 18 ft that is 4.6 ft out, at an angle of about 75.5 degrees.
How far above the roof should a ladder extend?
At least 3 feet above the edge, so that you can hold the rails as you step on and off.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.