System & Maintenance · DWG LS-012

ISO 4406 target cleanliness & filtration calculator

Set particle and moisture targets from machine type and criticality, then model filtration with a Schroeder mass-balance (ISO 16889 β-ratios). Forward mode predicts achievable ISO code; reverse recommends a filter; ΔP estimates clean-element pressure drop; Suggest picks a filter grade and housing.

Published standard (ISO 4406, ISO 16889, SAE AS4059)Last reviewed 14 Oct 2026

Source: Hy-Pro FCL filter cart brochure 2025 (PDF, distributor-hosted) · ISO 4406:2021 (iso.org) · ISO 16889:2022 (iso.org)

The filtration mass-balance model and ingression rates are planning estimates; filter options come from maker data.

Validation

The ISO 4406 / NAS 1638 / AS4059 code converter reproduces the published examples in ISO 4406:2021 4.4.5 (22/18/13), ISO 4406:2017 3.4.7 (14/12/≥7), Chevron Table 4 and the MP Filtri 2026 handbook NAS and AS4059G examples (automated test). These checks cover the converter, not the filtration model.

How calculators are checked: editorial standards.

Target Cleanliness & Dryness

Beginning targets for particles (ISO 4406) and water (ppm). Answer all six for a criticality-adjusted ISO + dryness target, see the Des-Case component guideline and a new-oil fill target (~2 codes cleaner), then optionally push the ISO into Filter Recommendation below.

Machine Type

Safety Risks Upon Failure

Cost of Downtime (hourly or daily)

Typical Length of Downtime

Material and Labor Costs to Repair

Effectiveness of Early Warning Systems

Des-Case guideline table (starting points)

Machine / configuration	Target ISO

Adjust up/down for criticality and risk appetite. New oil should typically be kept ~2 codes cleaner than the in-service target.

ISO 4406 Filtration Cleanliness

Current ISO Code (≥4µm / ≥6µm / ≥14µm)

Current oil analysis results (e.g. 22/20/17).

Filter Selection

Filter Micron Rating

Beta Ratio (β) at Rated Micron Hy-Pro G8 Dualglass media (FCL brochure 2025, β_x[C] ≥ 4000): 05M 0.9 µm(c) · 1M 3 · 3M 4 · 6M 6 · 10M 11 · 16M 16 · 25M 22 µm(c). Example: 10M element → 11 µm(c) / β 4000.

Reservoir Volume

Filter Flow Rate

Circulation Time or Passes

1 pass = entire reservoir volume pumped through the filter once.

ISO Viscosity Grade (VG)

Operating Conditions (Ingression)

These factors estimate contaminant ingression into the system. Worse conditions mean the filter must work harder and the achievable cleanliness will plateau higher.

Ingression Basis Default: typical plant (all factors ×1) ≈ 41.7 / 11.5 / 1.45 particles ≥4/6/14 µm per mL per minute — the rate that settles at 16/14/11 with a β₆=200 filter turning the tank over 10 %/min.

Operating Environment

Breather / Vent Type

Seal Condition

System Type

Filter Suggestion Inputs

Target code + flow + volume + ingression → required β at 4/6/14 µm → coarsest glass grade that delivers it → viscosity at operating and cold-start temperature → clean ΔP for each housing (≤ 10 % of bypass, no bypass at cold start) → media allowed by the fluid and temperature limits.

Oil

Temperatures: Operating / Cold Start / Maximum

Operating sets ΔP and the viscosity factor on β; cold start checks the bypass; maximum gates media and housing temperature limits.

Fluid Family

Filter Location

System Pressure at the Filter (psi)

Bypass Setting

Snap derived β to the standard tiers (as the other modes do) The unsnapped result is always shown beside it.

Filter ΔP Inputs

Calculates clean-element pressure drop across the filter at operating conditions. A loaded/dirty element will have higher ΔP — use this as a clean baseline only.

Oil

Operating Temperature

Flow Rate (GPM)

Filter element Known element: the maker’s published ΔP factor is used (psid/gpm at 32 cSt, SG 0.86). Otherwise the generic model applies.

Element bypass (FCL element type)

Assembly Factor Housing geometry / inlet-outlet loss multiplier. Use 1.0 for element-only ΔP. Increase for manifold housings, tight inlet geometry, or multi-element assemblies (typical range 1.0–2.0).

Cleanliness Code Converter — ISO 4406 · NAS 1638 · SAE AS4059

Pick a standard, then turn the dials, type a code or enter particle counts. The equivalent in the other standards is shown underneath. Uses the published tables only (ISO 4406:2021, SAE AS4059G, NAS 1638); it does not change the filtration model above.

ISO 4406 Code ≥4 / ≥6 / ≥14 µm(c) per mL. Microscope codes: -/16/13 or 16/13 (≥5 / ≥15 µm). Also accepts ≥7 (fewer than 20 particles counted), * (too many to count) and >28.

Turn a dial: drag or swipe it, scroll over it, use the ▲ ▼ buttons or the arrow keys. Small numbers under each value are the upper count limit per mL.

Or enter particle counts (cumulative, µm(c))

Counts are particles at or above each size

≥4 µm(c)

≥6 µm(c)

≥14 µm(c)

More sizes (optional): ≥21, ≥38, ≥70 µm(c) for full AS4059 and NAS 1638 classes

≥21 µm(c)

≥38 µm(c)

≥70 µm(c)

Most particle counters report these sizes too. AS4059 Table 1 (and NAS 1638) needs the 14–21, 21–38, 38–70 and >70 µm(c) bands.

Exact boundary values belong to the lower code: 1,300 per mL is scale 17 (ISO 4406 ranges are "more than … up to and including"). Counts drive the dials; turning a dial clears them.

ISO 4406 code

—

NAS 1638 is inactive for new designs but is still widely specified, for example in offshore subsea specifications. Conversions between NAS 1638, ISO 4406 and AS4059 are approximate because the size bands differ.

Editions & sources

ISO 4406:2021 (4th edition, Jan 2021; reviewed and confirmed by ISO on 29 Jun 2026, so it is still current). Scale numbers 0–28 and >28 are the same as in the 2017 edition. The 2021 change: particle contamination monitors (PCMs) calibrated to ISO 21018-3/-4 may now be used to report the code, as well as APCs calibrated to ISO 11171.
SAE AS4059G (revised Nov 2022; replaces Rev F of 2013, reaffirmed 2020). Table 1 (differential, B–F) uses the same limits as NAS 1638. Table 2 (cumulative, A–F, classes 000–12) is reported as “cpc”. ISO 11218:2017 (aerospace) adopts AS4059F.
NAS 1638 (AIA): inactive for new designs after 30 May 2001 (see AS4059). The latest issue says it is not for use with automatic particle counters.
Microscope counts (-/x/y codes) follow ISO 4407, revised in Dec 2025 (ISO 4407:2025).
ISO ↔ NAS read-across (approximate): MP Filtri and Invicta charts (NAS N ≈ ISO N+11/N+9/N+6) and the Chevron chart (N+10/N+9/N+6). The estimate uses the ≥6 and ≥14 µm(c) numbers, where the charts agree. The worse size sets the class.

ISO 4406:2021 Table 1 · SAE AS4059G Tables 1–2 (MP Filtri reprint, 2026) · NAS 1638 · cross-checked against Parker, Chevron, Hy-Pro and Invicta

The tables are reprints. Check the purchased standard before using a value for acceptance testing.

Show full table

ISO 4406:2021 — allocation of scale numbers

Particles per mL. Each range runs from “more than” up to and including the upper value. Tap a number in the ≥4, ≥6 or ≥14 column to set that dial.