AGMA Gear Oil Numbers and ISO VG Viscosity Grades: A Cross-Reference Guide for Industrial Gearboxes

Last verified: 2026-07-17

Suppose a gearbox comes in for service with a nameplate that reads "AGMA 5 EP," and the quotation on the desk offers a product described only as "ISO VG 220." A conversion table says the two match. The table is not wrong — and acting on it alone is still a sourcing error, because the two designators are not the same kind of label. ISO VG, defined in ISO 3448, classifies viscosity only: a nominal kinematic viscosity at 40°C (KV40) with a defined tolerance band around that midpoint. The AGMA lubricant number, historically defined in ANSI/AGMA 9005, carried more than viscosity — rust and oxidation inhibition, antiscuff (extreme-pressure) additive chemistry, or compounded fatty-oil content for worm gears lived in a suffix attached to the number. A cross-reference converts the viscosity component and nothing else.

The viscosity survives the conversion; the performance category does not. Every "AGMA 5 EP → ISO VG 220" substitution silently drops the "EP" unless the buyer restates it separately. That is why the table below is a starting point for verification, never a specification match — and why the RFQ data block near the end of this guide specifies measurements instead of a converted name. For the underlying additive chemistry and the ISO 12925-1 category system in general, see the platform's industrial gear oils deep-dive; this guide stays narrowly on the cross-reference itself.

What does an AGMA lubricant number actually designate?

The current governing document is ANSI/AGMA 9005-F16, "Industrial Gear Lubrication," approved as an American National Standard on 23 March 2016. It is a revision of ANSI/AGMA 9005-E02, which was itself a revision of 9005-D94. A 2023 AGMA Request-for-Interpretation (RFI 23-1) references 9005-F16 directly (specifically its Annex B viscosity-grade-selection tables), confirming the F16 edition was still the governing text as of that date. Checks of the ANSI Webstore, the AGMA/Motion + Power Manufacturers Alliance standards store, and GlobalSpec's standards listing found no later edition (no "9005-G," no logged reaffirmation, no withdrawal notice) at the time of this review; the current status should still be re-confirmed at the ANSI Webstore before any procurement or compliance decision is finalized on it.

The standard's scope covers lubricant classifications, minimum performance-characteristic guidelines, and generalized application and servicing guidance for both open and enclosed metallic gearing — spur, helical, worm, non-offset bevel, and face gears. It explicitly excludes grease-lubricated gearboxes and aerospace applications.

Historically, the AGMA number carried a suffix that identified the lubricant's performance category, not just its viscosity:

• R&O ("Rust & Oxidation," inhibited) — petroleum or synthetic base oils formulated with rust, oxidation, and foam-control additives, with no antiscuff (extreme-pressure) chemistry.
• AS ("Antiscuff") — the current terminology in 9005-F16 for what was historically labelled "EP" (Extreme Pressure). Industry trade coverage of the 9005-F16 revision reports that the standard directs users to transition from "EP" to "Antiscuff," on the basis that "EP" is too general a term and does not adequately describe the lubricant type or performance required. This description could not be independently confirmed against the ANSI Webstore's own preview PDF (it returned an access error when checked for this article); the exact wording should be confirmed against the purchased standard text before it is quoted in a technical document.
• Compounded — a mineral base fluid blended with fatty-oil content, traditionally used in worm-gear drives. This corresponds to the CKE category in the ISO 12925-1 classification (discussed further below).

The AGMA number today is widely treated in the industry as a legacy label that gets mapped onto an ISO VG grade for convenience. How far that treatment can be stated as a description of the standard's own internal structure is addressed in the section on why the mapping is approximate.

How does ISO 3448 define an ISO VG grade — and what does it leave out?

ISO 3448 defines the ISO viscosity grade (ISO VG) system. ISO 3448:1975 was withdrawn in 1992; ISO 3448:1992, together with corrigendum ISO 3448:1992/Cor 1:1993, is the current active edition. ISO's own standard record shows it was last periodically reviewed and reconfirmed in 2023, with no newer edition or withdrawal notice found at the time of this review. This should still be re-confirmed at iso.org before the standard is relied upon for a live procurement decision.

Each ISO VG number represents the nominal mid-point kinematic viscosity in mm²/s (cSt) at 40°C, with a tolerance band defined around that midpoint. This is the key fact governing everything else in this article: ISO VG is a viscosity-only classification. It says nothing about additive chemistry, base-oil type, or performance category. An "ISO VG 220" oil is guaranteed to fall within a defined viscosity band at 40°C and nothing else.

Third-party technical references (including Engineers Edge and the Anton Paar Wiki) consistently report the tolerance band as ±10% of the nominal midpoint, and this figure is arithmetically consistent with the published cross-reference table below (for example, ISO VG 46 spans 41.4–50.6 cSt, which is 46 × 0.9 to 46 × 1.1). This tolerance figure has not been independently confirmed against the purchased ISO 3448:1992 text and should be verified there before being treated as authoritative. The practical implication is worth stating plainly: two products both correctly labelled "ISO VG 220" can legitimately differ by up to roughly 10% in KV40, in either direction, and both remain fully in-spec. They are not identical oils.

Where does the commonly published cross-reference table come from — and how far can it be trusted?

The table below is the commonly published cross-reference reconstructed from third-party technical references (including ÖleZol and Machinery Lubrication/Noria, the latter independently confirming the AGMA 5 → VG 220, AGMA 6 → VG 320, and AGMA 7 → VG 460 mappings shown here). It is not reproduced from the purchased ANSI/AGMA 9005-F16 or ISO 3448 text. It is included here only to illustrate the structure of the correspondence, and every value in it must be confirmed against the standards themselves — the ANSI/AGMA 9005-F16 document and ISO 3448:1992 — before it is used to support a controlling specification.

⚠️ A note on consistency: at least one other third-party gear-oil chart, sourced explicitly to an older AGMA standard (250.04) rather than to 9005, publishes a materially different AGMA-number-to-ISO-VG assignment (each AGMA number shifted by roughly one grade). This is exactly the kind of inconsistency that makes a converted grade name unreliable on its own — it reinforces, rather than undermines, the caution below.

*The AGMA 11 upper bound follows the ±10% pattern seen across the rest of this table (3,200 × 1.1 = 3,520), but sources disagree: one third-party table (ÖleZol) that otherwise matches every other row in this table exactly instead shows 2,880–3,250 for AGMA 11 — a figure that breaks the ±10% pattern its own other rows follow. Neither figure was independently confirmed against the purchased standards for this article. This row specifically should be checked separately before use.

Published sources cannot even agree on one of this table's thirteen rows. That is the confidence level a converted grade name deserves on its own.

Why is the mapping only approximate, never a specification match?

This is the point on which the entire article turns, and it deserves the most attention of any section here. There are five distinct reasons the cross-reference cannot be treated as an equivalence.

The ISO VG tolerance band means two "matching" oils are not necessarily the same viscosity. Because each ISO VG grade is a band of roughly ±10% around a midpoint rather than a single value, the band itself spans roughly 20% of the nominal midpoint value (for ISO VG 220: 242 − 198 = 44 cSt, which is 20% of 220). Two oils sitting at opposite edges of the same band — one at −10%, the other at +10% of nominal, both still fully in-spec — can therefore differ from each other by close to 44 cSt at VG 220, or roughly 22% relative to the lower of the two readings. However it is expressed, the point stands: "same ISO VG number" does not mean "same viscosity," and a cross-reference table inherits this imprecision, which compounds further if the source product's actual measured KV40 sits near one edge of its band rather than at the center.

AGMA numbers and ISO VG grades are not the same kind of designator — this is the strongest reason of all. The historical AGMA system carried performance-category information in its suffix (R&O, Antiscuff/EP, Compounded) that the ISO VG number carries nowhere at all, because ISO VG is a viscosity-only classification. Cross-referencing "AGMA 5 EP" to "ISO VG 220" silently drops the antiscuff performance requirement the moment the conversion is made, unless the buyer separately and explicitly restates that requirement. The viscosity band survives the conversion; the performance category does not.

KV40 alone says nothing about how an oil behaves at the gearbox's actual operating temperature. Two oils can share an identical KV40 — and therefore an identical ISO VG grade — while having different Viscosity Index values (measured per ASTM D2270), meaning their actual viscosity, and the resulting lubricant film thickness, will differ once the gearbox reaches its real running temperature. A cross-reference table built purely on the 40°C figure cannot capture this difference; Viscosity Index has to be checked separately on the product's technical data sheet.

The AGMA standard's own revision history makes any cross-reference a moving target. ANSI/AGMA 9005 has been revised across three known editions — D94, E02, and F16 — and the F16 revision changed the terminology itself, moving from "EP" to "Antiscuff/AS." A cross-reference table published against an older edition's terminology may not align cleanly with how a product referencing the current 9005-F16 edition is actually labelled today.

Regional and era conventions do not always line up cleanly. Some published gear-oil literature, and some older gearbox nameplates still in service, use pre-ISO viscosity systems such as Saybolt Universal Seconds (SUS) rather than a metric kinematic viscosity. Where that is the case, a further conversion step is needed before an ISO VG match is even possible at all. No specific SUS-to-ISO-VG conversion factor is stated here, as none was independently verified for this article; the point should be treated qualitatively — as a reminder that an extra conversion layer can exist — rather than as a numeric shortcut.

Which requirements does a nameplate like "AGMA 5 EP" actually state?

When a nameplate or OEM manual reads "AGMA 5 EP," two separate things need to be matched, not one: the viscosity band (which the cross-reference approximates as ISO VG 220, subject to the caveats above) and the antiscuff/EP performance requirement itself. A plain R&O oil at the same viscosity is not a substitute for an antiscuff-rated product, regardless of how closely the KV40 numbers line up. The exact naming convention used on any specific real nameplate is site- and OEM-specific, so it should always be verified against that OEM's own manual rather than assumed from a generic table.

When a specification reads only "ISO VG 220" — with no AGMA reference and no stated R&O or antiscuff designation — the buyer has a viscosity match and nothing more. Nothing in "ISO VG 220" by itself confirms the presence of antiscuff additive chemistry, worm-gear compounded chemistry, micro-pitting resistance, or a synthetic base requirement. Each of those has to be confirmed separately, against the OEM manual or the gearbox manufacturer directly.

Several axes should never be substituted on viscosity alone:

• Antiscuff/EP requirement. A viscosity-matched R&O oil used in a gearbox specified for antiscuff service carries a real risk of scuffing or wear failure.
• Worm-gear compounded chemistry (ISO 12925-1's CKE category). Standard antiscuff sulfur-based chemistry, at the treat rates typical of enclosed-gear antiscuff oils, can corrode bronze worm-wheels. A viscosity-matched antiscuff oil is the wrong chemistry for a worm drive unless the OEM confirms compatibility.
• Micro-pitting resistance. Precision enclosed gearboxes — wind-turbine and machine-tool applications, for example — may require documented FVA 54/FZG test results. Viscosity matching alone says nothing about micro-pitting performance, and an FVA 54 pass should never be assumed for any product without the supplier's own test report.
• Food-grade certification (e.g. NSF H1). A viscosity or AGMA-to-ISO-VG cross-reference carries no food-grade information whatsoever; it sits on a wholly separate certification axis that has to be confirmed independently.
• Synthetic base requirement. AGMA's legacy "S" suffix describes base-oil chemistry — a different axis from viscosity entirely. ISO 12925-1 carries an equivalent distinction: its 2024 edition further subdivides the synthetic side of the classification into several more specific categories, rather than the simpler pairing used in older editions, so the exact applicable code should be confirmed on the supplier's technical data sheet rather than assumed. A mineral oil at the matching ISO VG grade is not a substitute if a synthetic base has been specified.

What should a buyer actually put in an RFQ — the data, not the converted grade name?

The practical fix for all of the above is straightforward: specify the underlying data rather than relying on a converted grade label. Save this block — pasted into an RFQ through the platform's RFQ Center, it replaces a converted name with the data a supplier can actually quote against:

• KV40 and KV100, with the test method named — ASTM D445 — rather than a grade name alone.
• Viscosity Index (VI), per ASTM D2270.
• The OEM's own designation, captured exactly as printed on the gearbox nameplate or manual — whether that is an AGMA number with its suffix, or an ISO VG number with a category letter — so the cross-reference step is visible and checkable rather than silently assumed by whoever compiled the RFQ.
• The applicable ISO 12925-1:2024 category — the CKB/CKC/CKD/CKE mineral-oil family, plus whichever synthetic sub-category applies (the 2024 edition splits these more finely than older editions did) — since this is where performance-category information lives in the current classification system, not in the ISO VG number itself. (The detail of what each category covers is addressed in the platform's industrial gear oils category guide, not here.)
• An explicit yes/no statement on the antiscuff/EP requirement, since the ISO VG number will not carry this information on its own.
• Micro-pitting requirement (FVA 54 result), for precision, wind-turbine, or machine-tool gearboxes where this applies.
• A technical data sheet (TDS) with named test methods for each parameter, not just headline numbers, and — where the application warrants it — a batch-specific certificate of analysis (COA). TDS values are typical values; a COA reflects the specific batch being supplied.

Buyers can review listed industrial gear oil products in the platform's industrial gear oils category and submit these specific data requirements directly through the RFQ Center rather than relying on a supplier's stated "AGMA equivalent" alone.

Which traps catch importers and distributors most often?

An importer or distributor who cross-references a supplier's AGMA-numbered product sheet against a customer's ISO-VG-stated requirement — or the reverse — risks silently dropping the antiscuff/R&O/compounded distinction that lived in the original AGMA suffix. The safer practice is to re-state the performance category explicitly in any documentation passed along to the customer, rather than passing along only the converted viscosity grade.

North American OEM documentation and gearbox nameplates have historically tended to use AGMA numbers, while European and most other markets have defaulted to ISO VG designations. No statistic on the relative prevalence of each convention was verified for this article, so this should be understood only as a general, qualitative pattern rather than a quantified market split.

A product sheet claim of "equivalent to ISO VG 220" should be read as a starting point for verification, not as a specification match. The claim by itself carries no information about additive category, Viscosity Index, or suitability for any specialized application, unless the sheet separately and explicitly states those things.

Because ANSI/AGMA 9005 has been revised multiple times, older stock or documentation still in the supply chain may use pre-F16 terminology ("EP" rather than "Antiscuff/AS"). An importer cross-referencing an older product sheet against a current requirement should confirm which edition's terminology the seller's sheet is actually using before assuming equivalence.

Where does the viscosity-grade cross-reference logic break down entirely?

Worm gears. The ordinary AGMA-to-ISO-VG viscosity cross-reference does not resolve the chemistry question at all for worm drives. Compounded oils — historically the AGMA "CP" suffix, corresponding to the ISO 12925-1 CKE category — exist specifically because standard antiscuff sulfur chemistry can corrode a bronze worm-wheel. A worm-gear buyer who matches only on viscosity or ISO VG number, without separately confirming compounded or synthetic (e.g. PAG-based) chemistry, risks sourcing the wrong product regardless of how precisely the viscosity numbers align. The viscosity can match perfectly while the chemistry corrodes the wheel.

Open gears. Open-gear and adhesive residual lubricants fall under an entirely separate designation family in the ISO 12925 series — ISO 12925-2, not Part 1 (Part 1 covers only enclosed gear systems: the CKB/CKC/CKD/CKE family). ISO 12925-2 specifies the CKH, CKJ, and CKM categories for open and semi-enclosed gear systems. An AGMA number or ISO VG viscosity cross-reference built around the enclosed-gear table above has no defined meaning for these open-gear compounds. These products are typically heavy, adhesive, and often solvent-cut-back lubricants, evaluated against criteria such as adhesion, residual film thickness, and throw-off resistance — none of which a viscosity-grade table is built to capture. No specific open-gear ISO VG or AGMA correspondence was verified for this article, and none is presented here; the category mismatch should be treated as a qualitative fact, not a numeric one.

The mistake this guide exists to prevent is a quiet one: a suffix dropped during a routine conversion, surfacing months later as scuffing, corrosion, or a dispute over who specified what. The fix costs one extra paragraph. Specify KV40/KV100, Viscosity Index, the ISO 12925-1 category, and an explicit antiscuff yes/no in the RFQ — and let the supplier quote against data instead of a converted name. Buyers can review listed products in the platform's industrial gear oils category and raise exactly that data request through the RFQ Center.

Standards referenced in this article — ANSI/AGMA 9005-F16 and ISO 3448 in particular — are periodically reviewed and reaffirmed by their issuing bodies. Before using any figure, table entry, or terminology point in this article for a live procurement or compliance decision, confirm the current edition and exact wording directly with ANSI/AGMA or ISO.

Frequently asked questions