How to Calculate Extension Ladder Size

Using an extension ladder safely begins with knowing the size of the ladder. Ladder sizes can be reckoned in any of three ways. The size of the ladder when fully closed is important if you wish to transport the ladder. The full-extended size is important so that you know whether the ladder is tall enough to reach the target height, and the safe working height is the height--plainly marked on the highest rung on which a person can stand safely--you should not go past when you climb the ladder.

Measuring tape

Instructions

- 1
  Measure the length of the ladder with a measuring tape when it is fully closed. This tells you how long the ladder will be when it's being carried by people or atop a work truck.
- 2
  Lay the ladder on the ground and extend the ladder fully. Measure from the bottom of the side rails at the bottom of the ladder to the top of the side rail on the extension, or "fly." This tells you the absolute maximum height of the ladder.
- 3
  Leave the ladder laying on the ground and measure from the bottom of the ladder to the rung marked as the highest safe standing level. This tells you the safe working height of the ladder.

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