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ISO VG Viscosity Grade Chart: Midpoint and Range at 40 C

ISO VG is the standard way to label industrial oil thickness. The number is the kinematic viscosity midpoint in centistokes (cSt) measured at 40 degrees Celsius, so ISO VG 68 is about 68 cSt at 40 C. Use the table to check a lubricant against an equipment spec or to confirm what a substitution means.

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ISO VG gradeMidpoint at 40 C (cSt)Minimum at 40 C (cSt)Maximum at 40 C (cSt)Typical use (general guidance)
ISO VG 2
2.2
1.98
2.42
Very light spindle and instrument oils
ISO VG 3
3.2
2.88
3.52
Very light spindle oils
ISO VG 5
4.6
4.14
5.06
High-speed spindles
ISO VG 7
6.8
6.12
7.48
High-speed spindles, light machine tool oils
ISO VG 10
10
9
11
Spindles, light hydraulic systems
ISO VG 15
15
13.5
16.5
Light hydraulic systems, spindles
ISO VG 22
22
19.8
24.2
Light hydraulics, small machine tools
ISO VG 32
32
28.8
35.2
Hydraulic systems, turbines, light-duty compressors
ISO VG 46
46
41.4
50.6
Hydraulic systems, vane pumps, compressors
ISO VG 68
68
61.2
74.8
Hydraulics in warm service, machine slideways, light gearboxes
ISO VG 100
100
90
110
Slideways, light gear drives
ISO VG 150
150
135
165
Industrial gearboxes
ISO VG 220
220
198
242
Industrial gearboxes, conveyors
ISO VG 320
320
288
352
Heavily loaded gearboxes
ISO VG 460
460
414
506
Heavily loaded gearboxes, slow-speed drives
ISO VG 680
680
612
748
Worm gears, very slow heavy drives
ISO VG 1000
1000
900
1100
Very slow heavy gear drives, open gearing
ISO VG 1500
1500
1350
1650
Very slow heavy gear drives, open gearing

The minimum and maximum are the grade midpoint minus and plus 10 percent, as defined in ISO 3448. The typical use column is general guidance only: always follow the equipment manufacturer's lubricant specification and operating temperature.

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How to read the table

Each grade has a midpoint and a permitted band of plus or minus 10 percent. An oil that measures 70 cSt at 40 C is ISO VG 68. An oil that measures 76 cSt falls outside that band and sits between grades 68 and 100, so it is not a standard ISO VG oil. Look up the grade named on the machine plate or in the OEM manual and compare it to the product data sheet.

  • Grade number equals the midpoint viscosity in cSt at 40 C
  • Allowed band is minus 10 percent to plus 10 percent
  • Viscosity falls as temperature rises, so the figure at 40 C is a label, not the working value
  • Check viscosity index when the machine runs hot or cold

ISO VG is not SAE and not AGMA

SAE grades such as 10W-30 or SAE 90 use different test temperatures and methods, and AGMA gear grades use their own numbers. They overlap with ISO VG but are not interchangeable by name alone. Use the viscosity at 40 C on the product data sheet to compare, and use the manufacturer's conversion chart when moving between systems.

Using it in the CMMS and storeroom

Lubricant consolidation is a quick win: many plants stock six or more grades where three would do. Use the table to find grades that sit next to each other and decide which can be merged. Record the ISO VG grade and product in the lubrication task on the preventive maintenance plan so that the right oil is requested, and keep an item record per product in the ERP so it can be reordered by grade.

Common mistakes

The most frequent mistake is topping up with a different grade because it was on the shelf. Mixing a VG 32 into a VG 68 system changes the working viscosity and may also mix additive packages. Other errors are ignoring operating temperature, and assuming a thicker oil is always safer: oil that is too thick raises energy use and can starve a bearing at start-up.

Frequently Asked Questions

What does ISO VG 46 mean?

It means the oil has a kinematic viscosity of about 46 cSt at 40 degrees Celsius, with an allowed band of 41.4 to 50.6 cSt. It says nothing about additives, base oil type or viscosity index, so two VG 46 oils can behave differently at other temperatures.

Can I replace ISO VG 68 with ISO VG 46?

Only if the equipment manufacturer allows it. A thinner oil gives a thinner film at operating temperature, which may increase wear in a loaded gearbox or pump. Always check the OEM lubricant chart and the actual operating temperature before changing grade.

Why is viscosity measured at 40 C?

ISO 3448 uses 40 C as the common reference temperature so that oils from different producers can be compared. The machine may run much hotter, so for operating viscosity you also need the oil's viscosity index or its value at 100 C.

What is the unit cSt?

A centistoke is one hundredth of a stokes, a unit of kinematic viscosity. It equals one square millimetre per second (mm2/s) in SI units. Data sheets use cSt and mm2/s interchangeably for the same number.

We can help link lubricant grades to equipment and PM tasks in your ERP so that the right oil shows up on every lube work order.

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