Ladder Size
18 ft
Reach
17.2 ft
Setback
3.4 ft
Recommended Ladder
18 ft
Extension Ladder
Safe Configuration
Must extend 3 ft above roof/landing
Inputs
Result
Target 13 ft wall height. At 75.5° angle, ladder length = 13 / sin(75.5°) + 3 ft deduction = 13 / 0.968 + 3 = 16.4 ft. Rounded up to 18 ft (nearest even). Setback from wall: 13 / tan(75.5°) = 3.4 ft.
Inputs
Result
Person reach = 5.67 ft + 1.5 ft overhead = 7.17 ft. Standing height needed = 9 - 7.17 = 1.83 ft. Add 2 ft deduction for top-step rule = 3.83 ft. Rounded to 4 ft minimum, but 6 ft step ladder recommended for comfort.
For extension ladders, you need a ladder 3–4 feet longer than the height you want to reach, because the top 3 feet must extend above the support point and the base sits away from the wall. A 1-story roof (13 ft) needs a 16–20 ft extension ladder. A 2-story roof (22 ft) needs a 24–28 ft ladder.
| Task | Height | Extension Ladder | Step Ladder |
|---|---|---|---|
| Gutter cleaning | 10 ft | 16 ft | 8 ft (if accessible) |
| 1-story roof | 13 ft | 20 ft | N/A |
| Paint 2-story | 20 ft | 24 ft | N/A |
| 2-story roof | 22 ft | 28 ft | N/A |
The 4-to-1 rule means the base of an extension ladder should be 1 foot away from the wall for every 4 feet of ladder height. This creates a 75.5° angle, which provides the best balance of stability and strength. A 20-foot ladder should have its base 5 feet from the wall.
On a step ladder, never stand on the top two steps (or top cap). On an extension ladder, your feet should be at least 3 rungs from the top. Standing too high on any ladder moves your center of gravity above the support point, making it unstable.
Step ladders are self-supporting and best for indoor work, painting, and tasks where you can't lean against a wall. Extension ladders lean against a structure and reach much higher. Use step ladders up to 10–12 feet of reach; extension ladders for anything above that.
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Last Updated: Mar 19, 2026
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