How to Determine Ladder Length Needed

Step 1: Measure the Height of the Support Point

Measure the vertical distance from the ground to the highest point you need to reach, such as a roofline, window, or gutter. This measurement represents the "height of the support point."

Step 2: Determine the Appropriate Overlap

Ladders should extend at least three feet (0.9 meters) above the support point. This ensures proper stability and prevents the ladder from slipping. So, add three feet to the "height of the support point" to get your total desired ladder height.

Step 3: Calculate Ladder Length

Use the formula: Ladder length = Desired ladder height ÷ Sine of the angle of inclination

- The "desired ladder height" is the value obtained in Step 2, which includes three feet of overlap.

- The "angle of inclination" is typically recommended by ladder manufacturers. A commonly recommended angle is 75 degrees (or 0.785 radians).

Example Calculation

Let's say you measured the height of the support point as 12 feet (3.7 meters). Using a 75-degree angle of inclination:

Ladder length = 15 feet (12 feet + 3 feet) ÷ Sine of 0.785 radians (75 degrees)

Ladder length = 15 feet ÷ 0.951 = 15.78 feet

Therefore, you would need a ladder approximately 16 feet long for this project (rounding up to the nearest foot).

Note: Safety should be your top priority when working with ladders. Follow all safety guidelines and instructions provided by the ladder manufacturer. Consider using a spotter or additional safety measures, especially when working at greater heights.