Enter the water line length (ft), the beam (ft), and the draft (ft) into the Wetted Surface Area Calculator. The calculator will evaluate the Wetted Surface Area. 

Wetted Surface Area Formula

The following formula is used to calculate the Wetted Surface Area. 

WSA = WLL * (B+D)


  • WSA is the Wetted Surface Area (ft^2)
  • WLL is the water line length (ft) 
  • B is the beam (ft) 
  • D is the draft (ft) 

To calculate the wetted surface area, multiply the water line length by the sum of the beam and draft.

How to Calculate Wetted Surface Area?

The following steps outline how to calculate the Wetted Surface Area.

  1. First, determine the water line length (ft).
  2. Next, determine the beam (ft). 
  3. Next, determine the draft (ft). 
  4. Next, gather the formula from above = WSA = WLL * (B+D).
  5. Finally, calculate the Wetted Surface Area.
  6. After inserting the variables and calculating the result, check your answer with the calculator above. 

Example Problem:

Use the following variables as an example problem to test your knowledge.

water line length (ft) = 20

beam (ft) = 10

draft (ft) = 5

WSA = WLL * (B+D) =  ?