Question: what is the formula to find the length?
Answer: Determining Length or Width When You Know the Other If you know the width, it's easy to find the length by rearranging this equation to get L = A ÷ W. If you know the length and want the width, rearrange to get W = A ÷ L. Example: The area of a rectangle is 20 square meters, and its width is 3 meters.