Unit systemDisplacement volume (> 0)Immersed midship section area (> 0)Lpp, length between perpendiculars (> 0)I confirm all three geometry values use the selected units and refer to the same draft and loading state.

Cp = displacement volume / (immersed midship section area × Lpp). Metric: m³, m², m. Imperial: ft³, ft², ft. The result is dimensionless.

Educational geometry only. All values must refer to the same draft and loading state. This tool explicitly uses Lpp (length between perpendiculars), not LWL. It does not assess stability, resistance, propulsion, seaworthiness or regulatory compliance. Cp above 1 is displayed for input review, not certified as valid hull geometry.

NOAA repository, List of Symbols: Cp = displaced volume / (midship area × length). That source defines its length as LWL; this calculator uses the explicitly stated Lpp convention.

A QUICK WALKTHROUGH

How to use this tool

Choose consistent metric or imperial units.
Enter positive geometry values from the same draft and loading state, then confirm their consistency.
Calculate, then copy or download the report.

Formula and units

Cp = displacement volume / (immersed midship section area × Lpp). Metric: m³, m², m. Imperial: ft³, ft², ft. The result is dimensionless.

Scope

Local processing

Inputs stay in your browser. Copy and TXT export include the inputs, calculation, formula and scope.

Reference

NOAA repository, List of Symbols: Cp = displaced volume / (midship area × length). That source defines its length as LWL; this calculator uses the explicitly stated Lpp convention. https://repository.library.noaa.gov/view/noaa/42563/noaa_42563_DS1.pdf

GOOD TO KNOW

Common questions

Can I enter displacement mass?

No. Enter displaced volume, not mass or tonnage. No density conversion is performed.

Does Cp prove vessel safety?

No. This is a geometric ratio only.