Bilge Pump Sizing Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Bilge Pump Sizing Calculator
Is your bilge pump actually big enough for your boat? This calculator applies a common rule-of-thumb sizing guideline based on hull dimensions.
Recommended GPH = Boat Length x Boat Beam x 20
Example
A 25 ft boat with an 8.5 ft beam:
Recommended GPH = 25 x 8.5 x 20 = 4,250 GPH minimum
Why Size Relative to Boat Dimensions
Larger boats have proportionally larger bilge volumes and higher potential water ingress rates in an emergency flooding scenario, which is why this sizing guideline scales with the boat's footprint (length x beam) rather than using a single flat GPH recommendation for every boat size.
Two Pumps, Not One
Most experienced boaters recommend installing at least two bilge pumps rather than relying on a single pump for both roles: a smaller automatic pump for routine, everyday water removal (rain, spray, minor seepage), plus a larger, high-capacity emergency pump specifically sized to handle serious flooding - a genuine hull breach or major water ingress event that a small routine pump simply couldn't keep up with.