Free Engineering Tool
Oil Viscosity Classes — ISO VG
Lookup ISO VG viscosity grade per ISO 3448. Enter kinematic viscosity at 40 °C to find the matching class, or select a VG grade to see the viscosity range and typical applications.
This calculator was developed and verified by the Vibromera engineering team, makers of the Balanset portable balancing instruments.
Results
ISO 3448 Viscosity Classification
ISO 3448 defines 18 viscosity grades for industrial lubricants. Each grade is identified by a number equal to the nominal kinematic viscosity midpoint at 40 °C in centistokes (cSt). The allowed range is ±10% of the midpoint.
Complete ISO VG Table
| ISO VG | Min (cSt) | Midpoint (cSt) | Max (cSt) | Typical Application |
|---|
Application Guide
| Application | Recommended ISO VG |
|---|---|
| High-speed spindles | VG 10 – VG 22 |
| Hydraulic systems | VG 32 – VG 46 |
| General machine lubrication | VG 46 – VG 68 |
| Industrial gearboxes | VG 68 – VG 150 |
| Heavy-duty enclosed gears | VG 220 – VG 460 |
| Very heavy / slow gears | VG 680 – VG 1500 |
Note: ISO VG grades specify viscosity at 40 °C only. The actual operating viscosity depends on the oil temperature in service. Use the Viscosity Index (VI) to estimate viscosity at other temperatures.
ISO VG (Viscosity Grade) is a classification system for industrial lubricants defined by ISO 3448. Each grade corresponds to a nominal kinematic viscosity at 40 °C in centistokes (cSt). The grade number equals the midpoint viscosity — for example, VG 46 means 46 cSt ± 10%.
There are 18 grades from VG 2 to VG 1500, each step being roughly 50% higher than the previous.
The optimal viscosity depends on the application and operating conditions:
- VG 10–22 — High-speed spindles, light loads
- VG 32–46 — Hydraulic systems (most common)
- VG 68–150 — Industrial gearboxes
- VG 220–460 — Heavy-duty enclosed gears
- VG 680–1500 — Very heavy/slow machinery
Always consult the equipment manufacturer's recommendations. Using too thin an oil leads to wear; too thick increases energy losses and heat.
ISO VG grades classify industrial lubricants by kinematic viscosity at 40 °C. SAE grades are used for automotive oils: SAE crankcase grades (e.g. 10W-30) and SAE gear grades (e.g. 75W-90) use different temperature references and scales.
The two systems do not directly correspond. Approximate cross-references exist — for example, ISO VG 46 ≈ SAE 20, ISO VG 150 ≈ SAE 40 — but these are only rough equivalents.
Oil viscosity decreases as temperature increases. ISO VG grades specify viscosity at 40 °C only. The rate of viscosity change with temperature is described by the Viscosity Index (VI).
A higher VI means less viscosity change with temperature. Typical mineral oils have VI 80–100; synthetic oils can reach VI 150+. For critical applications, always verify viscosity at the actual operating temperature.
cSt (centistokes) is the unit of kinematic viscosity, equal to mm²/s. It measures how quickly a fluid flows under gravity. The related unit cP (centipoise) measures dynamic viscosity.
Conversion: cP = cSt × density (density in g/cm³). For typical mineral oil at ~0.87 g/cm³, cP ≈ cSt × 0.87.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional field balancing instruments and software. Used in 50+ countries for rotating machinery maintenance.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
