Choked Flow Critical Pressure Ratio Calculator

Choked Flow Critical Pressure Ratio Calculator

Past a certain point, dropping downstream pressure further stops increasing flow through a restriction entirely - that point is defined by the critical pressure ratio, and it depends only on the gas's specific heat ratio.

Formula: P_crit/P₀ = (2/(γ+1))^γ/(γ-1)

For air (γ = 1.4), this works out to the well-known critical ratio of about 0.528 - a figure widely used in compressible flow and safety relief valve design.

How to Use This Calculator

1. Enter the gas's specific heat ratio (gamma) - 1.4 for air and most diatomic gases, 1.33 for many combustion gases, 1.67 for monatomic gases like helium.

When the downstream-to-upstream pressure ratio drops below this critical value, flow through the restriction becomes "choked" - velocity at the throat reaches the local speed of sound, and mass flow rate becomes independent of further downstream pressure reduction.