Filter Beta Ratio Calculator

Convert between beta ratio, capture efficiency and particles passed: β = upstream ÷ downstream counts, efficiency = (1 − 1/β) × 100 — the ISO 16889 multipass terms.

Hydraulics 5 inputs 3 results

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Beta ratio (β)

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Beta ratio(β)

200

Pass

At or above the β = 200 (99.5%) level commonly marketed as an absolute rating.

β ≥ 75 is the common minimum for a "rated" filter; β ≥ 200 is the typical absolute-rating threshold.

Also computed

Capture efficiency(η)99.5%

Passed per million challenged5,000

The linear way to read β: 1,000,000 ÷ β particles get through.

Method notes 4 notes

Definition math from the ISO 16889 multipass test: β(x) = upstream ÷ downstream counts at particle size x. The rating is meaningless without its size — β200 at 10 µm and at 3 µm are different filters.
Efficiency compresses near 100% while contamination does not: β200 → 99.5% and β1000 → 99.9% sound close, but the β200 filter passes five times as many particles.
Real circuits recirculate: system cleanliness settles where ingression and capture balance, so target ISO 4406 cleanliness codes drive the β you need — the maker's data sheet maps one to the other.
Dirt-holding capacity, pressure-drop growth and bypass cracking are the other half of filter selection and live in the catalog, not this ratio.

Filter ratings are count ratios from the ISO 16889 multipass test: β(x) = upstream ÷ downstream particle counts at the rating size, efficiency = (1 − 1/β) × 100. The ladder runs β2 = 50%, β75 ≈ 98.7%, β200 = 99.5% (the common "absolute" threshold), β1000 = 99.9% — and the honest comparison is particles passed per million (10⁶/β), where β200 lets through five times more than β1000. This calculator converts between counts, β and efficiency in any direction.

How to use this calculator

Fix the particle size. The β value travels with its micron rating — your servo valve or pump spec names the size that matters.
Convert to the linear view. Particles passed per million = 10⁶/β — the honest way to compare 99.5% vs 99.9%.
Check against the cleanliness target. System ISO 4406 codes drive the β you need; the filter maker’s data sheet maps one to the other.
Select on the rest of the catalog. Dirt-holding capacity, ΔP growth and bypass cracking pressure finish the selection.

How it works

Filter ratings are count ratios from the ISO 16889 multipass test: challenge the element with particles of the rating size, count both sides, divide:

β(x) = N_up / N_down · η = (1 − 1/β) × 100% · passed/million = 10⁶/β

The ratio form exists because the percentages crowd together at the top while the contamination consequences do not. Downstream of the filter, the numbers feed the rest of the circuit's hygiene story — the heat load that ages oil, the line velocities that stir it, and the actuators whose seals and valves the cleanliness class protects.

Worked example

Verified against the live calculator

A multipass report shows 100,000 particles ≥10 µm per mL upstream and 500 downstream:

β10 = 100,000 / 500 = 200 → 99.5% capture, 5,000 per million passed

Compare a β1000 element at the same size: 99.9% capture, 1,000 per million — one-fifth the particles through, though the efficiency column barely moves. If the system must hold a tight ISO 4406 code for servo valves, that 5× difference is the whole argument.

Frequently asked questions

What does a beta ratio of 200 mean?

For every 200 particles of the rating size that reach the filter, one gets through: β = upstream ÷ downstream counts, so β200 is 99.5% capture efficiency — 5,000 particles passed per million challenged. It is the level commonly marketed as an "absolute" rating.

How do you convert beta ratio to efficiency?

Efficiency = (1 − 1/β) × 100. The canonical ladder: β2 = 50%, β75 ≈ 98.7%, β200 = 99.5%, β1000 = 99.9%. The inverse is β = 1 / (1 − η/100).

Why does beta ratio matter more than the efficiency percentage?

Because efficiency compresses near 100% while contamination does not: 99.5% and 99.9% sound nearly identical, but the β200 filter passes five times as many particles as the β1000. Reading filters in beta (or particles passed) keeps the comparison linear.

What is the beta ratio measured at?

A specific particle size from the ISO 16889 multipass test — the rating is written β5 ≥ 200 or similar, and it is meaningless without the size. A filter that is β200 at 10 µm may be barely β2 at 3 µm; match the size to what your most sensitive component cares about.

Method & assumptions

Definition math only (ISO 16889 multipass terms); no media, micron-rating or dirt-capacity data is embedded — the filter maker's test report governs.
β is size-specific: every output here belongs to the particle size the counts were taken at.
Single-pass capture ratio; real circuits recirculate, so steady-state cleanliness settles where ingression and capture balance.
The β75/β200 context bands are commonly used industry thresholds, not a standard's acceptance limits.