Work out filter pressure drop instantly with clear inputs, formula shown and shareable results.
Filter resistance is published at a 500 fpm face velocity and rises with roughly the 1.6 power of velocity for pleated media. Dust loading then multiplies that clean value, typically by two before change-out. The extra pressure is paid for in fan power for every hour the filter stays in place.
Face velocity
V = CFM / face area ft²
Loaded drop
Δp = rated drop x (V / 500)^1.6 x loading factor
Fan penalty
kW = CFM x Δp extra / (6356 x fan efficiency) x 0.7457
V = CFM / face area ft². Filter resistance is published at a 500 fpm face velocity and rises with roughly the 1.6 power of velocity for pleated media.
Common practice is at twice the clean pressure drop, or at the manufacturer's stated final resistance, whichever comes first. Waiting longer starves the coil of airflow.
This calculator takes 4 inputs: Airflow through filter, Filter face area, Clean drop at 500 fpm rating, Dirty-to-clean loading factor. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.