Measure all three aspects of ladder length using a tape measure. Measure the length of the closed extension ladder for transporting and storage purposes. Extend the telescopic fly section to the last position supported by the rung locks, and measure the ladder from end to end to figure its extended length. Then measure from the base to the third rung from the top, as that is the highest rung on which a worker can safely stand.
Measure the length of an extension ladder against its duty rating. Heavy-duty and extra-heavy-duty, or type 1 and type 1A, extension ladders can extend up to 60 feet in two sections and up to 72 feet in three-sections. Medium-duty type 2 ladders are safe up to 48 feet in two sections and 60 feet in three sections. Light-duty type 3 ladders are made only in two sections and are safe up to 32 feet.
Measure the distance between rungs. OSHA recommends equal spacing between ladder rungs. The spacing should be 10 to 14 inches.
Measure the width of the base and fly sections. These may be considerations for storage and transporting, but there are no mandates regarding ladder width and safety.