ISO 3448
ISO VG chart
An ISO viscosity grade is a window of kinematic viscosity at 40°C. The midpoint is the number in the name, except for VG 2, 3, 5, and 7, whose midpoints are 2.2, 3.2, 4.6, and 6.8 mm²/s. Every window is ±10% of its midpoint. ISO 3448 does not specify the viscosity at 100°C, the viscosity index, or the additive type.
Finished charts that compare branded oils are on oilviscositychart.com. This table is the standard’s windows, plus two illustrative 100°C columns.
| ISO VG | Min | Midpoint | Max | 100°C, VI 95 | 100°C, VI 150 |
|---|---|---|---|---|---|
| 2 | 1.98 | 2.2 | 2.42 | — | — |
| 3 | 2.88 | 3.2 | 3.52 | — | — |
| 5 | 4.14 | 4.6 | 5.06 | — | — |
| 7 | 6.12 | 6.8 | 7.48 | 2.06 | 2.23 |
| 10 | 9 | 10 | 11 | 2.64 | 2.90 |
| 15 | 13.5 | 15 | 16.5 | 3.38 | 3.79 |
| 22 | 19.8 | 22 | 24.2 | 4.25 | 4.86 |
| 32 | 28.8 | 32 | 35.2 | 5.29 | 6.27 |
| 46 | 41.4 | 46 | 50.6 | 6.64 | 8.10 |
| 68 | 61.2 | 68 | 74.8 | 8.53 | 10.9 |
| 100 | 90 | 100 | 110 | 11.1 | 14.5 |
| 150 | 135 | 150 | 165 | 14.5 | 19.6 |
| 220 | 198 | 220 | 242 | 18.7 | 25.9 |
| 320 | 288 | 320 | 352 | 24.0 | 34.1 |
| 460 | 414 | 460 | 506 | 30.3 | 44.2 |
| 680 | 612 | 680 | 748 | 39.1 | 58.2 |
| 1000 | 900 | 1000 | 1100 | 49.9 | 76.0 |
| 1500 | 1350 | 1500 | 1650 | 64.2 | 99.8 |
The 100°C figures on this page are illustrative. ISO 3448 specifies the grade at 40°C only. Each column is the viscosity of an oil that hits the grade midpoint at 40°C and the stated viscosity index, solved with ASTM D2270, then moved to other temperatures with the ASTM D341 Walther equation (constant 0.7). A dash means that viscosity index would put the oil below 2 mm²/s at 100°C, where ASTM D2270 does not define VI. Use the data sheet in the converter when you have one.
How to use the window
A fresh oil at 46.0 mm²/s and 40°C is ISO VG 46. An oil at 38 mm²/s and 40°C is in the gap between VG 32 (max 35.2) and VG 46 (min 41.4). It has no ISO VG. An oil at 46 mm²/s and 80°C is not ISO VG 46. The grade is a 40°C classification.
Gear oils you will actually pour are usually VG 68 and heavier. The grades with their own temperature pages are VG 220, VG 320, and VG 460. Choosing among them for a gearbox is covered under pitch-line velocity.
Questions
Does ISO VG 220 mean 220 cSt at every temperature?
No. It means the kinematic viscosity at 40°C falls between 198 and 242 mm²/s. At any other temperature the viscosity is whatever that oil’s viscosity-temperature curve says.
Why are there gaps between grades?
The grades are a preferred-number series with a ±10% tolerance, and 10% of each midpoint does not reach the next window. A measured 40°C viscosity in a gap is reported as the number, not forced into a grade.