Pa to CFM Calculator

Convert Pascal (Pa) pressure differential to Cubic Feet per Minute (CFM) airflow for HVAC, ventilation, and engineering applications.

HVAC Calculator:

Convert pressure measurements to airflow rates using orifice flow principles for accurate ventilation and system design calculations.

Airflow Converter

Conversion Direction

Pressure differential across the orifice

Cross-sectional area of the orifice

kg/m³

Air density (default: 1.225 kg/m³ at STP)

C

Flow coefficient (default: 0.6 for sharp-edged orifice)

Airflow Results

Enter pressure and area, then click "Convert"

to calculate airflow rate

Pa to CFM Airflow Conversion

In HVAC and ventilation systems, engineers often need to convert pressure measurements in Pascal (Pa) to airflow rates in Cubic Feet per Minute (CFM). These measurements represent different physical quantities, so conversion requires additional parameters like orifice area and air properties.

This calculator uses the standard orifice flow formula, which is commonly applied in ductwork design, fan selection, and ventilation system analysis. The calculation accounts for real-world factors like discharge coefficient and air density for accurate results.

Why Pressure Alone Isn't Enough

Pressure difference tells you the force driving the airflow, but to find the actual volume of air moving, you need to know the size of the opening and the properties of the air itself. Different orifice sizes and air conditions will produce different flow rates for the same pressure.

  • Orifice area: Larger openings allow more air to flow
  • Air density: Heavier air flows differently than lighter air
  • Discharge coefficient: Accounts for real-world flow inefficiencies
  • Temperature and humidity: Affect air density and flow characteristics

Airflow Conversion Formula

The calculator uses the orifice flow equation for compressible fluids:

CFM Calculation:
CFM = (C × A × √(2 × ΔP ÷ ρ)) × 2118.88
*Where C=discharge coefficient, A=area (m²), ΔP=pressure (Pa), ρ=density (kg/m³)
Reverse Calculation:
Pa = ((CFM ÷ 2118.88) ÷ (C × A))² × ρ ÷ 2
*Converts airflow back to pressure differential

HVAC Airflow Examples

Here are typical pressure to airflow conversions used in ventilation system design:

Pressure (Pa) Area (m²) Air Density (kg/m³) Result (CFM)
50 0.02 1.225 135 CFM
100 0.03 1.225 286 CFM
250 0.05 1.2 720 CFM
75 0.025 1.225 203 CFM
150 0.04 1.225 488 CFM
25 0.015 1.225 68 CFM
200 0.035 1.2 553 CFM
125 0.028 1.225 315 CFM
300 0.06 1.2 1037 CFM
40 0.018 1.225 97 CFM
175 0.045 1.225 667 CFM
85 0.022 1.225 187 CFM
225 0.055 1.2 825 CFM
60 0.024 1.225 162 CFM
350 0.065 1.2 1269 CFM
95 0.026 1.225 249 CFM
275 0.048 1.2 781 CFM
35 0.016 1.225 75 CFM
180 0.042 1.225 607 CFM
120 0.032 1.225 365 CFM
400 0.07 1.2 1538 CFM
65 0.021 1.225 138 CFM
240 0.052 1.2 785 CFM
Engineering Note:

For precise HVAC calculations, always use measured values for discharge coefficient and verify air density under actual operating conditions. This formula assumes incompressible flow for most ventilation applications.