The Bulk Modulus ($K$) is a measure of the fluid’s resistance to compression under pressure. It quantifies how much a fluid’s volume changes in response to a change in pressure while keeping the temperature constant. The Bulk Modulus is defined as the ratio of the change in pressure to the resulting fractional change in volume. The SI unit of Bulk Modulus is the Pascal (Pa) or Newton per square meter (N/m²). The formula for Bulk Modulus is given by:

Where:

• $K$ is the Bulk Modulus,
• $V$ is the volume of the fluid,
• dP/dV​ is the rate of change of pressure with respect to volume.