Calculate boat hull or pipe wetted surface area from length, beam, draft, radius and coverage, then estimate marine anode requirements.

Wetted Surface Area Calculator

Choose a tab, enter values, then calculate.

Boat Hull
Cylinder / Pipe
Anode Lookup
Boat Hull Wetted Surface Area
Typical quick estimate uses k = 1.00.
Cylinder or Pipe Wetted Surface Area
Hull Anode Lookup by Wetted Surface Area
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Wetted Surface Area Formula

There is no single exact closed-form formula for a boat’s wetted surface area because it depends strongly on hull shape. The formula below is a common rule-of-thumb used by the calculator’s Quick method to estimate the underwater hull area (excluding appendages unless you add them separately).

WSA \approx LWL \times (B + T) \times k

Variables:

  • WSA is the wetted surface area (e.g., ft² or m²)
  • LWL is the waterline length
  • B is the beam at the waterline
  • T is the draft
  • k is an empirical hull factor (dimensionless) used to tune the estimate

To estimate wetted surface area with this rule-of-thumb, multiply the waterline length by the sum of the beam and draft, then multiply by the hull factor k.

How to Calculate Wetted Surface Area?

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

  1. First, determine the waterline length (LWL).
  2. Next, determine the beam at the waterline (B).
  3. Next, determine the draft (T).
  4. Next, gather the formula from above: WSA ≈ LWL × (B + T) × k.
  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.

Waterline length, LWL (ft) = 20

Beam, B (ft) = 10

Draft, T (ft) = 5

WSA ≈ LWL × (B + T) × k (using k = 1.00) = 20 × (10 + 5) × 1.00 = 300 ft²