How to Calculate the Ladder Length for the Job

Ladders are used by people completing maintenance and construction work in commercial and residential buildings. Despite being a simple tool, each year an average of 300 people are killed and approximately 65,000 people are injured when using ladders. Alongside length considerations, a ladder is rated by standards set by the American National Standards Institute for the maximum weight capacity. Each ladder sold in the U.S. should carry a label giving the manufacturers recommendations for the maximum height the ladder should be used for.

Tape measure

Instructions

- 1
  Assess the work environment in which the ladder is to be used. Choose which type of ladder is needed. A stepladder is best used indoors; an extension ladder is best for outdoor jobs. Measure the height of the area at which an individual will be working using a tape measure.
- 2
  Subtract the height of the work area from the length of the ladder. A worker cannot stand on the top rungs of a ladder and must ensure the ladder extends beyond the work area by at least the length of the top three rungs.
- 3
  Refer to the manufacturers recommended working height to ensure the ladder is usable at the required working height. An extension ladder should extend beyond the required working height or above a roof that needs to be accessed.
- 4
  Subtract the unusable amount of ladder from the fully extended length of an extension ladder. For extension ladders up to 32 feet in length, 3 feet of the ladder is unusable, ladders above 32 feet to 36 feet have 4 feet of unusable length. The top three rungs of each extension of a ladder should not be used as they do not provide a safe amount of support for the user.
- 5
  Subtract 4 feet from the height to be accessed using a stepladder to obtain the length of stepladder to be used. For example, a 7-foot working height requires a 3-foot stepladder.

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