Hydraulic Oil ISO VG Viscosity Grade Reference
ISO VG numbers are the language of industrial lubricant purchasing. This table lists each grade defined in ISO 3448 with the actual cSt range at 40 C and where each is commonly applied.
| ISO VG grade | Minimum at 40 C (cSt) | Mid-point at 40 C (cSt) | Maximum at 40 C (cSt) | Typical application |
|---|---|---|---|---|
ISO VG 2 | 1.98 | 2.2 | 2.42 | Spindle and very light precision lubrication |
ISO VG 3 | 2.88 | 3.2 | 3.52 | Spindle and light instrument oils |
ISO VG 5 | 4.14 | 4.6 | 5.06 | High speed spindles and light machine oils |
ISO VG 7 | 6.12 | 6.8 | 7.48 | Light machine tool and spindle oils |
ISO VG 10 | 9 | 10 | 11 | Spindles and light-duty hydraulics |
ISO VG 15 | 13.5 | 15 | 16.5 | Low temperature hydraulics, machine tool slideways |
ISO VG 22 | 19.8 | 22 | 24.2 | Cold climate and low-temperature hydraulic systems |
ISO VG 32 | 28.8 | 32 | 35.2 | Common indoor industrial hydraulics, vane pumps |
ISO VG 46 | 41.4 | 46 | 50.6 | Most widely specified general hydraulic oil grade |
ISO VG 68 | 61.2 | 68 | 74.8 | Hot environments, heavy-duty hydraulics, light gear oil |
ISO VG 100 | 90 | 100 | 110 | Light gearboxes, slideways, large circulating systems |
ISO VG 150 | 135 | 150 | 165 | Industrial gear drives, way lubricants |
ISO VG 220 | 198 | 220 | 242 | Industrial enclosed gear drives |
ISO VG 320 | 288 | 320 | 352 | Heavily loaded enclosed gear drives |
ISO VG 460 | 414 | 460 | 506 | Heavy gear drives and slow-speed bearings |
ISO VG 680 | 612 | 680 | 748 | Heavy gear drives, open gearing at low speed |
ISO VG 1000 | 900 | 1,000 | 1,100 | Very heavy gear drives and slow, high-load applications |
ISO VG 1500 | 1,350 | 1,500 | 1,650 | Worm gears and very slow, heavily loaded drives |
Grades follow the ISO 3448 system: the number is the mid-point kinematic viscosity in cSt at 40 C, and each grade allows plus or minus 10 percent. Applications listed are common practice, not a specification. Always follow the pump or gearbox manufacturer's allowed viscosity window at operating temperature, and check viscosity index (VI) because two oils of the same grade can differ widely at 100 C.
Lubricant spec lookup
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How to use it
Search by grade or by application. Match the grade to the viscosity window in the pump manual, which is usually given in cSt at operating temperature, not at 40 C. For example, many piston pumps want 16 to 36 cSt for best efficiency and tolerate 10 to 1000 cSt briefly during cold start. Use the table to pick a grade, then check where that grade lands at your real oil temperature using the viscosity index from the product data sheet.
- Pick the grade, then verify viscosity at running temperature
- Check the minimum viscosity at maximum temperature
- Check the maximum viscosity at cold start
- Avoid mixing grades or oil families without compatibility checks
The ISO 3448 system
ISO 3448 defines 18 industrial liquid lubricant viscosity grades from VG 2 to VG 1500. The grade number is the mid-point kinematic viscosity in centistokes at 40 C. A tolerance of plus or minus 10 percent defines the minimum and maximum. Grades are spaced by a geometric series so that each step is roughly 50 percent higher than the last. The system is independent of base oil or additive package, so it says nothing about oil quality, viscosity index, wear additives or oxidation life.
Reading the table and choosing a grade
ISO VG 46 is the default for general hydraulic work in temperate indoor plants. VG 32 helps in cooler spaces or with pumps that prefer lower viscosity, while VG 68 suits hot ambient conditions or oil running near 150 F. Moving up one grade usually lowers internal leakage and raises pump efficiency at high temperature, but raises cold-start drag and pumping losses. If oil temperature swings widely, a high-VI multigrade fluid often gives a better operating window than shifting grade.
Common mistakes
The usual error is confusing ISO VG with SAE viscosity grades, which use different test temperatures and are not interchangeable with a simple conversion. Another is switching grade to solve a leak or noise problem without checking temperature. Do not rely on grade to infer quality; compare the datasheet VI, pour point, antiwear package and demulsibility, and confirm any OEM approval such as the pump maker's fluid specification.
Frequently Asked Questions
What does the number in ISO VG 46 mean?
It is the mid-point kinematic viscosity in centistokes at 40 C. An ISO VG 46 oil can measure anywhere from 41.4 to 50.6 cSt at 40 C under ISO 3448.
Is ISO VG the same as SAE grade?
No. SAE engine and gear grades use different temperatures and test methods. Comparison charts are approximate, so use the product datasheet for the exact viscosity at both 40 and 100 C.
Can I switch from VG 46 to VG 68?
Only after checking the pump's viscosity window at your hottest and coldest oil temperature, and the filter and cold-start limits. A flush may be needed to avoid mixing oil families.
What is viscosity index?
VI measures how much viscosity changes with temperature. A higher VI means less change. High-VI oils give a wider usable temperature range for the same ISO grade.
Netray can connect lubricant specifications and oil analysis records to a private assistant so techs can look up the right grade for a specific asset.
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