Pressure Drop Calculator

This calculator estimates how much pressure a compressed air system loses between the compressor and the point of use, combining true fluid-dynamics friction loss with typical equipment drops. The piping portion uses the Darcy-Weisbach equation — pressure drop is proportional to the friction factor, the ratio of pipe length to diameter, and air density times velocity squared. The friction factor itself is computed from the Reynolds number and pipe roughness (using a Swamee-Jain approximation to the Colebrook equation for turbulent flow), so a longer, narrower, or higher-velocity run all independently drive the drop up. Air density and actual velocity are both corrected for the fact that free-air CFM compresses as it enters the pressurized line — the calculator converts your input flow to actual conditions at the system pressure before running the physics.

On top of the pipe friction, it adds flat per-component allowances: 2.5 psi for each inline filter and 4.0 psi for each dryer, both typical "new equipment" figures rather than measurements of your specific hardware — a dirty filter can easily double that. The tool assumes commercial steel pipe roughness and roughly 100°F air; it doesn't take separate temperature or roughness inputs despite what older guidance text may suggest, so results are an engineering estimate for planning, not a substitute for a field pressure survey. The energy penalty uses the standard rule of thumb that every 2 psi of drop costs about 1% more compressor energy. As a rule of thumb, keep total drop under 10% of supply pressure — anything higher usually means it's time to upsize pipe or service dirty filters and dryers.