Ladder Size Chart: Heights, Reach & Weight Ratings

Reach is not the same as ladder length

A 16 ft extension ladder does not let you work 16 ft up. Set at 75°, it loses 3 ft to section overlap and to the angle itself, so its max reach is 12.5 ft. A step ladder is the opposite: a 8 ft step ladder lets you work 8.0 ft up — you stand two rungs down (the top two rungs are off-limits) and your arms add about 2 ft. On the defaults — a 12.0 ft task — the recommended ladder is Extension 16 ft with a reach of 12.5 ft, the needed extension length is 15.5 ft and the base distance is 3.2 ft.

Ladder size chart — type, size, max reach, duty rating, rung spacing

Every reach cell is the formula to 1dp, half-up — derived from the size value, never hand-typed. Step ladders: reach = size. Extension, multi-position and telescoping ladders: reach = size × sin(75°) − 3 ft. All rows show the common Type IA 300 lb duty rating — ratings vary by model and the label on the ladder governs. At the defaults — 12.0 ft — the recommended ladder is Extension 16 ft (reach 12.5 ft), the needed extension length is 15.5 ft and the base distance is 3.2 ft. Check the identities: extension reach = size × 0.9659258 − 3; needed extension length = (task height + 3) / 0.9659258; base distance = task height / 3.7320508. Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum.

The worked example, line by line

Setup: task height 12.0 ft.

Line 1 — the step ladders. The tallest step ladder is 10 ft with a reach of 10.0 ft — under 12.0 ft, so no step ladder reaches.

Line 2 — the extension ladders. The smallest extension ladder is 16 ft: 16 × 0.9659258 − 3 = 12.5 ft — over 12.0 ft, so the pick is Extension 16 ft.

Line 3 — the needed extension length. (12.0 + 3) / 0.9659258 = 15.5 ft — the ladder must extend to at least that length to reach the task.

Line 4 — the base distance. 12.0 / 3.7320508 = 3.2 ft — the 1-in-4 rule: 1 ft out for every 4 ft up.

Reverse: the max task height for an extension 24 ft ladder is 20.2 ft (exact 20.1822 ft). The ladder for an 18 ft task is Extension 24 ft (needed extension length 21.7 ft, reach 20.2 ft). The step ladder for a 7 ft task is Step 8 ft (Step 6 reaches 6.0 ft — under 7 ft). The base distance for a 20 ft task height is 5.4 ft (exact 5.3590 ft). The max task height for a step 10 ft ladder is 10.0 ft. The extension length for a 35 ft task is 39.3 ft → Extension 40 ft (reach 35.6 ft).

Every branch, checked

8 ft task: Step 8 ft (reach 8.0 ft), needed extension 11.4 ft, base 2.1 ft, step option Step 8 ft. A step ladder does it — the 8 ft step ladder reaches exactly 8.0 ft.

5 ft task: Step 6 ft (reach 6.0 ft), needed extension 8.3 ft, base 1.3 ft, step option Step 6 ft. The smallest step ladder that reaches is the 6 ft — the 4 ft step ladder reaches only 4.0 ft.

20 ft task: Extension 24 ft (reach 20.2 ft), needed extension 23.8 ft, base 5.4 ft. The 20 ft extension reaches only 16.3 ft, so the pick is the 24 ft extension at 20.2 ft.

30 ft task: Extension 40 ft (reach 35.6 ft), needed extension 34.2 ft, base 8.0 ft. The 32 ft extension reaches only 27.9 ft, so the pick is the 40 ft extension at 35.6 ft.

24 ft task: Extension 28 ft (reach 24.0 ft), needed extension 28.0 ft, base 6.4 ft. The 24 ft extension reaches 20.2 ft — under 24 ft — so the pick is the 28 ft extension at 24.0 ft.

10 ft task: Step 10 ft (reach 10.0 ft), needed extension 13.5 ft, base 2.7 ft, step option Step 10 ft. The tallest step ladder does it exactly — the 10 ft step ladder reaches 10.0 ft.

3.9 ft task: Step 4 ft (reach 4.0 ft), needed extension 7.1 ft, base 1.0 ft, step option Step 4 ft. The smallest step ladder reaches 4.0 ft — just enough.

What the defaults assume

The model assumes the 75° set-up rule (1 ft out for every 4 ft up) and 3 ft of section overlap on extension ladders, and that the top two rungs of a step ladder and the top three rungs of an extension ladder are off-limits. It assumes the reach figures are the highest point the ladder lets you work at, not the height of the ladder itself, and that the Type IA 300 lb rating on every row is the common rating — ratings vary by model and the label on the ladder governs. At a 0 ft task height the pick is Step 4 ft — any ladder reaches, so the smallest step ladder is the pick. At a 40 ft task height No ladder in the chart reaches 40.0 ft — the 40-ft extension reaches 35.6 ft — model-level, the page recommends a professional or a lift, it is not a calc error. Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum; the reverses are nearest-value solutions, and the exact unrounded figures (20.1822 ft, 5.3590 ft) are stated wherever the rounded figures appear.

Output · formula · meaning

Who uses this

• The homeowner cleaning a 1-story gutter: they learn no step ladder reaches 12.0 ft — the tallest reaches 10.0 ft — so they need the Extension 16 ft — and they check the 8 ft branch (Step 8 ft (reach 8.0 ft), needed extension 11.4 ft, base 2.1 ft, step option Step 8 ft) for the step ladder.
• The painter doing an 8-ft ceiling: they learn the Step 8 ft reaches exactly 8.0 ft — and they check the 5 ft branch (Step 6 ft (reach 6.0 ft), needed extension 8.3 ft, base 1.3 ft, step option Step 6 ft) for the smaller jobs.
• The roofer reaching 2-story eaves: they learn the Extension 24 ft reaches 20.2 ft — and they check the 24 ft branch (Extension 28 ft (reach 24.0 ft), needed extension 28.0 ft, base 6.4 ft) for the taller eaves.
• The renter with no storage: they learn the telescoping 12.5 ft ladder reaches 9.1 ft and folds small — and they check the multi-position row (13.4 ft) for the all-rounder.

Accuracy & limitations

The math is first-principles geometry: extension reach = size × sin(75°) − 3 ft; needed extension length = (task height + 3) / sin(75°); base distance = task height / tan(75°). Every table cell is derived from the size value — the 24 ft extension cell is 24 × 0.9659258 − 3 = 20.2 ft, not a hand-typed number. The 4-decimal exact is shown where the rounding matters: the max task height for an extension 24 ft ladder is 20.1822 ft (shown as 20.2 ft); the base distance for a 20 ft task is 5.3590 ft (shown as 5.4 ft). What the model cannot do is keep you safe: it assumes a level, solid footing and a ladder in good condition — a soft lawn, a damaged rung, or a ladder set at the wrong angle changes everything, and the duty rating on the label governs, not the table. For the roof the ladder reaches, see the roof pitch chart; for the ramp that replaces the ladder, see the ramp slope calculator; for the air conditioner the ladder installs, see the air conditioner size chart; and for the slab the ladder stands on, see the concrete slab calculator. This is a calculator, not safety advice — read the label on your ladder.