Beta Ratio (β)
Definition
A dimensionless number expressing filtration efficiency: the ratio of particles of a given size upstream to those downstream of the filter.
Beta ratio is defined as βx = (particles ≥ x µm upstream) / (particles ≥ x µm downstream). A β₁₀ = 1000 means 1000 particles enter for every 1 that passes, equivalent to 99.9 % efficiency at 10 µm.
Efficiency (%) = (1 − 1/β) × 100. Common reference points are β = 2 (50 %), β = 20 (95 %), β = 200 (99.5 %) and β = 1000 (99.9 %). Beta values come from standardized multi-pass testing.
Relevance for high-flow filtration
Beta ratio lets engineers compare R+F absolute-rated media against OEM specifications on an objective, standardized basis.
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Related terms
A filtration rating stating that a defined percentage — typically 99.9 % (beta 1000) — of particles at or above the rated micron size is removed in a single pass.
Nominal FiltrationA filtration rating indicating an approximate particle-removal efficiency — commonly 50–90 % — at the stated micron size, without a guaranteed single-pass value.
Micron RatingThe nominal particle size, in micrometers (µm), that a filter is designed to remove — stated as either an absolute or a nominal value.
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