Calculate the Cavitation Number (K) for fluid systems by entering Local Pressure (p), Fluid Vapor Pressure (pv), Fluid Density (ρ), and Flow Characteristic Velocity (V). The dimensionless result tells you how prone your flow is to cavitation — lower values indicate higher cavitation risk in pumps, turbines, and hydraulic systems.
Cavitation Number (K)
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Pressure Difference (p − pv)
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Dynamic Pressure (½ρV²)
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Cavitation Risk Assessment
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The Cavitation Number (K) is a dimensionless parameter that expresses the relationship between the pressure difference of a local absolute pressure and the fluid vapor pressure, relative to the kinetic energy per unit volume of the flow. It is used to characterize how likely a fluid flow is to cavitate. A lower cavitation number indicates a higher risk of cavitation occurring.
The Cavitation Number is calculated as K = (p − pv) / (0.5 × ρ × V²), where p is the local absolute pressure, pv is the fluid vapor pressure, ρ is the fluid density, and V is the flow characteristic velocity. The numerator is the excess pressure above vapor pressure, and the denominator is the dynamic pressure of the flow.
A low cavitation number (approaching zero or below) indicates that the local pressure is close to or below the vapor pressure, meaning the fluid is likely to form vapor bubbles — a condition known as cavitation. Cavitation can cause significant damage to pumps, turbines, propellers, and other hydraulic equipment through erosion, noise, and vibration.
Vapor pressure is the pressure at which a liquid transitions to vapor at a given temperature. In cavitation analysis, it serves as the threshold — if the local pressure drops to or below the vapor pressure, the liquid boils locally and forms vapor cavities. For water at 20°C, the vapor pressure is approximately 2338 Pa.
This calculator uses SI units. Enter local pressure and vapor pressure in Pascals (Pa), fluid density in kilograms per cubic meter (kg/m³), and flow velocity in meters per second (m/s). The resulting Cavitation Number is dimensionless. Common reference values: water density ≈ 998 kg/m³ at 20°C, atmospheric pressure ≈ 101,325 Pa.
The Cavitation Number is widely used in fluid mechanics, hydraulic engineering, naval architecture, and mechanical engineering. It is especially important in the design and analysis of centrifugal pumps, hydraulic turbines, ship propellers, control valves, and any system where high-velocity liquid flow may encounter low-pressure regions.
Cavitation can be mitigated by increasing the local pressure (e.g., raising the inlet head or pressurizing the system), reducing the flow velocity, selecting fluids with lower vapor pressures, using cavitation-resistant materials, and optimizing the geometry of components such as pump impellers and valve passages to avoid sharp pressure drops.
There is no single universal safe value — the critical cavitation number depends on the specific geometry and application. In practice, system designers aim to keep K well above the critical threshold (K_crit) determined experimentally for each component. For many pumps and turbines, K values above 0.2–0.5 are generally considered safer, but this varies widely by design.