Ladder Height Chart: What Size Ladder Do I Need?

The ladder height chart

A ladder is a fit for the reach, not just a length: it should be tall enough to reach the work and short enough that you are not standing on the top rung. Too short and you climb past the top, which is how people fall. Too long and the ladder is heavy, hard to carry, and hard to set at the right angle. The rule is simple: the reach decides the size, and the lookup picks the smallest ladder that reaches — 12 ft takes the 8-ft step ladder, not the 16-ft extension, because the step ladder is the smallest ladder that reaches.

The sizes are the standard ladders the shops sell: 4 ft to 8 ft step ladders, and 16 ft to 28 ft extension ladders. The step-ladder reach is the height plus 4 ft, because you stand on the second rung from the top and reach up 4 ft. The extension-ladder reach is the length minus 3 ft, because the sections overlap by about 3 ft and the ladder leans at 75 degrees, and the ladder must extend 3 ft above the landing surface. The reach is the highest you can safely work, not the top of the ladder: never stand on the top two rungs of a step ladder, and never stand on the top three rungs of an extension ladder.

How to measure your reach

The sizing rule is reach first. Stand where the ladder will stand, and measure from the ground to the work in feet, not from the wall to the wall. A gutter is usually 10 to 12 ft up, which is the 8-ft step ladder. If you are between two ladders, take the larger one: a ladder that is a few feet too long is easier to live with than a ladder that is a foot too short, and you can always set it at a steeper angle.

The worked example, line by line

Setup: a target reach of 12 ft; find the ladder size.

Line 1 — the rule. A step ladder reaches its height plus 4 ft, so an 8-ft step ladder reaches 12 ft.

Line 2 — the smallest that reaches. The 4-ft step ladder reaches 8 ft and the 6-ft step ladder reaches 10 ft, so neither reaches 12 ft. The 8-ft step ladder reaches 12 ft, so the answer is the 8-ft step ladder.

Line 3 — the extension check. The 16-ft extension ladder reaches 16 − 3 = 13 ft, so it also reaches — but it is bigger and heavier than the step ladder, so the step ladder is the right one.

Line 4 — the reverse. A 24-ft extension ladder reaches up to 21 ft, so a job at 12 ft is well inside what it can do.

Every branch, checked

8 ft: 8 ft is the reach of the 4-ft step ladder (4 + 4 = 8 ft) — the smallest ladder in the chart, and the right one for a low gutter or a ceiling.

10 ft: 10 ft is the reach of the 6-ft step ladder (6 + 4 = 10 ft) — the size for a first-floor window or a high shelf.

17 ft: 17 ft is the reach of the 20-ft extension ladder (20 − 3 = 17 ft) — the size for a second-floor gutter. The 16-ft extension only reaches 13 ft, so it falls 4 ft short.

21 ft: 21 ft is the reach of the 24-ft extension ladder (24 − 3 = 21 ft) — the size for a high roof edge.

14 ft: 14 ft is more than the 16-ft extension reaches (13 ft), so the answer is the 20-ft extension ladder, which reaches 17 ft. The 16-ft extension falls 1 ft short — and a ladder that falls short is a ladder you climb past the top of.

Reverse — the 24-ft extension ladder: a 24-ft extension ladder reaches up to 21 ft, so a job at 12 ft is well inside what it can do. A 6-ft step ladder reaches up to 10 ft, so a job at 12 ft is 2 ft beyond it. If you already own the ladder, the reverse tells you how high you can safely work; if you are buying, the forward lookup tells you what to buy.

What the defaults assume

This chart is a ladder height chart only: it is not a weight-capacity chart — it does not say how much weight a ladder holds, which depends on the duty rating and the load — and it is not a paddle-length chart — it does not say which paddle length fits a kayak, which depends on the paddler and the boat — and it is not an OSHA-training chart — it does not say how to set, climb, or secure a ladder, which depends on the job and the training. It assumes a step ladder is used on flat ground and an extension ladder leans at 75 degrees: a ladder set at the wrong angle reaches less, and a ladder on soft ground sinks. It assumes the reach is the highest you can safely work: never stand on the top two rungs of a step ladder, and never stand on the top three rungs of an extension ladder. Rounding convention: all reaches are whole feet, and all figures are computed from the ladder size as written.

Output · formula · meaning

Who uses this

• The homeowner cleaning a gutter: they learn a gutter at 12 ft needs an 8-ft step ladder — and a 6-ft step ladder only reaches 10 ft, so it falls 2 ft short and they would climb past the top.
• The renter hanging a picture high on the wall: they learn a reach of 8 ft needs a 4-ft step ladder — and an 8-ft step ladder is too big, so it is heavy and hard to carry up the stairs.
• The homeowner painting a second-floor wall: they learn a reach of 17 ft needs a 20-ft extension ladder — and a 16-ft extension only reaches 13 ft, so it falls 4 ft short.
• The buyer who already owns a ladder: they learn a 24-ft extension ladder reaches up to 21 ft — so they know how high they can safely work, and whether the ladder they own fits the job they have.

Accuracy & limitations

The lookup is exact for the numbers you enter: the ladder comes from the target reach, and the reach comes from the ladder size by the step or extension rule. What the chart cannot do is know your ground: a ladder on soft ground sinks, and a ladder set at the wrong angle reaches less, so set the base a quarter of the working height out from the wall. It is explicitly not a weight-capacity chart — the duty rating depends on the ladder and the load — and not an OSHA-training chart — how to set, climb, or secure a ladder depends on the job and the training. It assumes a step ladder is used on flat ground and an extension ladder leans at 75 degrees. For the same idea on a roof, see roof pitch chart; for the same idea on a deck, see deck joist span chart.