Calculate filter pressure drop at your actual airflow by scaling the rated clean pressure drop and airflow, with an optional dirty-filter multiplier.

Initial (clean) resistance from the filter label or data sheet, at the rated airflow below.

Model assumptions
Default 2 is a square-law assumption, not a universal filter curve. Use a fitted exponent if supported by your filter data.

Blank means 1 (clean). A value such as 1.5 assumes 50% more resistance at the same flow; it does not predict dust loading.

Related Calculators

Filter Pressure Drop Formula

This calculator scales a rated clean-filter pressure drop for the same filter and air conditions. The power-law exponent and loading multiplier are assumptions, not universal properties.

ΔPclean = ΔPᵣated × (Qₐctual / Qᵣated)ⁿ; ΔPₗoaded = ΔPclean × M

Variables:

  • ΔP_rated is the clean pressure drop at the rated test airflow
  • Q_rated is the rated airflow (greater than zero)
  • Q_actual is the actual airflow (zero or greater)
  • n is the assumed positive flow exponent; default 2 is a square-law assumption
  • M is the assumed loading multiplier; blank means 1 (clean), and values must be at least 1
  • ΔP_clean and ΔP_loaded are the estimated clean and loaded pressure drops

Use the same flow units for the ratio, raise the actual-to-rated flow ratio to n, and multiply by rated pressure drop. Then multiply by M for the assumed loading scenario. The former equation was a pipe-friction expression and did not match this filter-scaling calculator.

What is Filter Pressure Drop?

Filter pressure drop refers to the reduction in pressure as a fluid flows through a filter. This drop in pressure is caused by the resistance the filter media provides to the fluid flow. The pressure drop is a critical parameter in the design and operation of filtration systems, as it affects the efficiency and performance of the filter. A higher pressure drop indicates a greater resistance to flow, which can lead to increased energy consumption and reduced flow rates. Understanding and managing pressure drop is essential for maintaining optimal filtration performance and ensuring the longevity of the filter.

How to Calculate Filter Pressure Drop?

The following steps outline how to calculate the Filter Pressure Drop.

  1. First, obtain rated clean pressure drop and rated airflow for your filter.
  2. Enter the actual airflow and select its unit.
  3. Use a flow exponent supported by the filter curve where possible; 2 is only an initial assumption.
  4. Optionally enter a loading multiplier of at least 1; blank means clean-filter resistance.
  5. Keep filter geometry and air conditions consistent with the rated test point.
  6. Select Calculate to estimate clean and loaded pressure drop. Zero actual flow gives zero in this model.
  7. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Rated clean pressure drop = 0.25 in. w.c.

Rated airflow = 1,200 CFM

Actual airflow = 900 CFM

Assumed exponent n = 2; loading multiplier M = 1.5

Clean drop = 0.25 × (900 / 1,200)² = 0.140625 in. w.c.; loaded drop = 0.2109375 in. w.c. This is a model example, not a measured filter rating.