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Lubricant Grade Decoder

Cross-reference ISO VG, AGMA, SAE engine, SAE gear, and NLGI. Type one grade, get the rest.

Lubricant grades come from several standards that do not line up by number, which is how a mechanic ends up thinking an SAE 90 gear oil is thicker than an SAE 50 engine oil when they are nearly the same viscosity. This decoder takes a grade on any common scale (ISO VG, AGMA, SAE engine, SAE gear, or NLGI grease) and reports the approximate equivalents on the others, anchored to the ISO VG number, which is the actual kinematic viscosity at 40 C. It carries the field-truth warnings the chart does not print: the SAE engine and gear scales are separate, the cross-references are approximate because the scales use different reference temperatures, and NLGI grades grease firmness, not viscosity, so it does not convert to an oil grade at all.

Pro Tip: Convert through viscosity, not through SAE numbers. SAE 90 gear oil and SAE 50 engine oil both land near ISO VG 220, but their SAE numbers (90 vs 50) make it look like the gear oil is far heavier. The engine and gear SAE classifications are separate scales. When in doubt, compare the kinematic viscosity at 40 C, which is exactly what the ISO VG number gives you.

Once you have the grade, estimate the relube or oil-change interval with the

Lube Interval Calculator →

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Lubricant Grade Decoder
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How It Works

  1. Enter a grade

    Type the grade you have: ISO VG 68, AGMA 5, 10W-30, SAE 90, or NLGI 2.

  2. Read the scale it belongs to

    The decoder identifies whether it is ISO VG, AGMA, an SAE engine grade, an SAE gear grade, or an NLGI grease.

  3. See the cross-reference

    For oils, it shows the ISO VG, the kinematic viscosity at 40 C, and the approximate AGMA and SAE engine and gear equivalents.

  4. Heed the engine-vs-gear note

    The decoder flags that engine and gear SAE numbers are different scales, so you do not compare them by number.

  5. Verify for a spec

    Cross-references are approximate. For a specific oil, check the kinematic viscosity on the data sheet against the requirement, and confirm thresholds against ISO 3448, SAE J300/J306, or AGMA 9005.

Built For

  • A millwright told to use an ISO VG 220 gear oil but the only label in the shop is "SAE 90".
  • A maintenance tech converting an old AGMA 5 callout to a modern ISO VG.
  • A mechanic checking whether a 10W-30 is anywhere near the ISO VG 100 a pump calls for.
  • A planner standardizing grease points and confirming NLGI 2 is the general-purpose grade.
  • Anyone confused about why the gear oil number is so much bigger than the engine oil number.

Features & Capabilities

Five scales, one anchor

ISO VG, AGMA, SAE engine, SAE gear, and NLGI, all related back to the ISO VG viscosity.

Engine-vs-gear warning

The single most common mistake is surfaced on every oil decode.

Grease handled honestly

NLGI is reported on its own consistency axis, not faked into a viscosity equivalent.

Approximation flagged

Cross-references are clearly labeled approximate because the scales use different reference temperatures.

Comparison

ISO VG cSt at 40 C AGMA SAE engine SAE gear
46 41.4-50.6 1 15W / 20 75W-80W
68 61.2-74.8 2 20 80W
100 90-110 3 30 80W-90
150 135-165 4 40 85W-90
220 198-242 5 50 90
320 288-352 6 60 90-140

References

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Frequently Asked Questions

No, they are about the same. Both land near ISO VG 220 (roughly 198 to 242 cSt at 40 C). The SAE engine and gear oils use separate viscosity classifications, so the bigger gear number does not mean a thicker oil. This is the most common lubricant mix-up. Always compare the actual viscosity, not the SAE number across the two scales.
The ISO VG number is the kinematic viscosity midpoint in centistokes (cSt) at 40 C, with a plus or minus 10 percent band. ISO VG 68 is 61.2 to 74.8 cSt at 40 C. Because the number is the real viscosity, ISO VG is the cleanest scale to convert through.
They track closely: AGMA 1 is about ISO VG 46, AGMA 2 is ISO VG 68, AGMA 3 is ISO VG 100, and so on up to AGMA 8 near ISO VG 680. AGMA EP and R&O variants share the viscosity but differ in additive package.
No. NLGI grades the consistency (firmness) of a grease using the ASTM D217 cone-penetration test, not a viscosity. NLGI 2 is the general-purpose grade. The base oil inside a grease has its own viscosity, which is a separate specification from the NLGI number.
Roughly ISO VG 100 by the SAE 30 hot grade, though engine oils are multigrade and defined at 100 C, so the comparison is approximate. The decoder uses the hot grade (the 30 in 10W-30) to estimate the ISO VG. For a precise number, check the kinematic viscosity at 40 C on the product data sheet.
Disclaimer: Viscosity cross-references (ISO VG, SAE engine and gear, AGMA, NLGI) returned by this decoder are approximate. The scales use different reference temperatures and overlapping bands, multigrade oils are defined at 100 C, and NLGI grades grease consistency rather than viscosity, so cross-grade conversions are estimates only. Always confirm the kinematic viscosity at 40 C and the additive package on the product data sheet and follow the equipment manufacturer's lubricant specification before selecting an oil or grease. This tool is for educational and reference purposes only.

Learn More

Shops & Outbuildings

Lubricant Viscosity Grades Explained

How ISO VG, AGMA, SAE engine, and SAE gear grades relate, why the engine and gear SAE scales are not comparable, and how NLGI grease consistency is a separate axis.

Read Guide →

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