ISO VG viscosity grade chart
An ISO VG grade gives the viscosity of an industrial oil at 40 °C. This page lists the limits of every grade from ISO VG 2 to ISO VG 1500 and the grades commonly used on each type of equipment.
What is ISO VG?
ISO VG (Viscosity Grade) is the viscosity classification of industrial lubricants defined in ISO 3448. The grade number is the midpoint of the oil's kinematic viscosity at 40 °C, in centistokes (cSt, mm²/s). Each grade allows a range of ±10% around the midpoint. For example, an ISO VG 68 oil must measure between 61.2 and 74.8 cSt at 40 °C.
ISO VG grades and limits
| Grade | Midpoint (cSt) | Minimum (cSt) | Maximum (cSt) | Typical use |
|---|---|---|---|---|
| ISO VG 2 | 2.2 | 1.98 | 2.42 | Precision spindles, light lubrication |
| ISO VG 3 | 3.2 | 2.88 | 3.52 | Precision spindles, light lubrication |
| ISO VG 5 | 4.6 | 4.14 | 5.06 | Spindles, light lubrication |
| ISO VG 7 | 6.8 | 6.12 | 7.48 | Spindles, light lubrication |
| ISO VG 10 | 10 | 9 | 11 | Spindles, cold-climate hydraulics |
| ISO VG 15 | 15 | 13.5 | 16.5 | Hydraulics and spindles, low temperature |
| ISO VG 22 | 22 | 19.8 | 24.2 | Hydraulics (low temperature), precision bearings |
| ISO VG 32 | 32 | 28.8 | 35.2 | Hydraulic systems, turbines, screw compressors |
| ISO VG 46 | 46 | 41.4 | 50.6 | Hydraulic systems (most common), turbines, compressors |
| ISO VG 68 | 68 | 61.2 | 74.8 | Hydraulics (hot, heavy duty), compressors, bearings |
| ISO VG 100 | 100 | 90 | 110 | Piston compressors, bearings, lightly loaded gearboxes |
| ISO VG 150 | 150 | 135 | 165 | Gearboxes, bearings, paper machine bearings |
| ISO VG 220 | 220 | 198 | 242 | Industrial gearboxes (most common), bearing lubrication |
| ISO VG 320 | 320 | 288 | 352 | Heavily loaded gearboxes, gear units |
| ISO VG 460 | 460 | 414 | 506 | Heavily loaded gearboxes, worm gears |
| ISO VG 680 | 680 | 612 | 748 | Worm gears, slow heavy gears |
| ISO VG 1000 | 1,000 | 900 | 1,100 | Very heavy load, slow gears |
| ISO VG 1500 | 1,500 | 1,350 | 1,650 | Very heavy load, slow gears and bearings |
Limits are ±10% of the midpoint (ISO 3448). The typical use column is general guidance. The grade to use depends on the machine manufacturer's recommendation, operating temperature, speed and load.
Common ISO VG grades by equipment
| Equipment | Common grades | Note |
|---|---|---|
| Hydraulic system | ISO VG 32, 46, 68 | VG 46 is the most common. VG 32 is used in cold conditions and VG 68 in hot conditions. |
| Steam and hydro turbine | ISO VG 32, 46, 68 | Turbine oils are concentrated in these three grades. |
| Screw compressor | ISO VG 32, 46, 68 | The compressor manufacturer's recommended grade applies. |
| Piston compressor | ISO VG 68, 100, 150 | Higher pressure and temperature call for a higher grade. |
| Industrial gearbox | ISO VG 150, 220, 320, 460 | VG 220 and VG 320 are the most common. |
| Worm gear | ISO VG 460, 680 | Sliding friction calls for high viscosity. |
| Rolling and plain bearings | ISO VG 32–220 | Higher speed calls for a lower grade, heavier load for a higher grade. |
| Paper machine dryer bearings | ISO VG 150, 220, 320 | Bearing lubrication circuits running at high temperature. |
The table summarises common practice. Always check the machine manufacturer's lubrication chart for the final choice.
Temperature and viscosity
Oil viscosity falls as temperature rises. The ISO VG grade gives the value at 40 °C, so at the machine's operating temperature the oil is thinner. The viscosity index (VI) shows how much viscosity changes with temperature. An oil with a high VI changes less with temperature.
An in-line sensor measures viscosity at the oil's actual temperature. So the reading cannot be compared directly with the VG number on the label. What matters is the trend on the same machine.
What a change in viscosity tells you
- Viscosity rising: The oil may have aged through oxidation or overheated. Topping up with the wrong oil can also raise viscosity.
- Viscosity falling: Fuel may have entered the oil, a lower grade may have been added, or the oil may have sheared.
- Viscosity stable: The oil is normal in this respect. Water, particles and ageing are monitored separately.
Other warning signs in oil and what to do
Request a quote to measure oil viscosity on site or continuously on your machine.
Questions about ISO VG
What does ISO VG 46 mean?
ISO VG 46 means the oil's kinematic viscosity at 40 °C has a midpoint of 46 cSt. The permitted range is 41.4–50.6 cSt. It is one of the most common grades in hydraulic systems. Details
What is the difference between ISO VG 32 and ISO VG 46?
ISO VG 46 is a thicker oil, so its viscosity is higher. The right grade depends on the machine manufacturer's recommendation, the operating temperature and the load. In general, a lower grade is used in cold conditions and a higher grade in hot conditions or under heavy load. Details
How much can viscosity change before the oil must be changed?
There is no single limit for every machine, and different guides quote different percentages. The ±10% range in the grade table applies to new oil and is not an alarm limit. The sound approach is to record the new oil's value as a baseline, follow the trend and decide according to the machine manufacturer's recommendation. Details
Can oil viscosity be measured on site?
Yes. A portable oil analyzer measures a sample on the spot. An online oil sensor measures viscosity continuously in the oil line. Laboratory measurement (ISO 3104, ASTM D445) remains the reference. Details