Filtration Efficiency Calculator

Calculate MERV/HEPA filter efficiency, CADR, penetration, and pressure drop for different particle sizes.

MERV Rating (1–20)

Particle Size Range

Airflow (CFM)

Filter Face Area (sq ft)

Tab to move between fields

Filter Efficiency (%)

80%

Penetration (%)20%

Clean Air Delivery Rate (CFM)320

Face Velocity (fpm)100

Est. Pressure Drop (in. w.g.)0.01

How to Use This Calculator

Enter MERV Rating (1–20), Particle Size Range, and Airflow (CFM).
Set Filter Face Area (sq ft).
Review the Filter Efficiency (%) (%) result.
Use Penetration (%) (%) and Clean Air Delivery Rate (CFM) to inform your decision.

How the result changes with MERV Rating (1–20)

MERV Rating (1–20): MERV 1–8 basic, 9–12 good, 13–16 superior, 17–20 HEPA-level.
Particle Size Range: 1 = 0.3–1 μm (smoke/bacteria), 2 = 1–3 μm (mold/fine dust), 3 = 3–10 μm (pollen/PM10).
Airflow (CFM): Air volume flowing through the filter in cubic feet per minute.
Filter Face Area (sq ft): Total face area of the filter. Standard 20×25 filter = ~3.5 sq ft.

Filter Efficiency (%): Percentage of particles captured by the filter at the selected size range.
Penetration (%): Percentage of particles passing through the filter.
Clean Air Delivery Rate (CFM): Effective volume of clean air delivered: airflow × efficiency.
Face Velocity (fpm): Air speed across the filter face. Ideal range: 300–500 fpm.
Est. Pressure Drop (in. w.g.): Estimated initial clean-filter pressure drop in inches of water gauge.

Identify Input Parameters
4 parameters
MERV Rating (1–20) = 13, Particle Size Range = 1, Airflow (CFM) = 400, Filter Face Area (sq ft) = 4 = 4 input(s) provided
Calculate Filter Efficiency
Filter Efficiency = getMervEfficiency(merv, particleSizeRange)
80 = 80%
Calculate Penetration
Penetration = 1 - efficiency
20 = 20%
Calculate Clean Air Delivery Rate
Clean Air Delivery Rate = airflowCfm * efficiency
320 = 320