ISO VG (Viscosity Grade) is a classification system for industrial lubricants defined by ISO 3448. Each grade corresponds to a kinematic viscosity midpoint at 40°C in centistokes (cSt). For example, VG 46 means the oil has a midpoint viscosity of 46 cSt at 40°C, with an allowed range of 41.4–50.6 cSt (±10%).

How to choose the right viscosity grade?

The choice depends on the application: VG 32–46 for hydraulic systems, VG 68–150 for industrial gearboxes, VG 220–460 for heavy-duty enclosed gears, VG 10–22 for high-speed spindles. Always consult the equipment manufacturer's recommendations.

What is the difference between ISO VG and SAE?

ISO VG grades are based on kinematic viscosity at 40°C and are used for industrial lubricants. SAE grades are used for automotive oils: SAE crankcase grades (e.g. 10W-30) are measured at 100°C, while SAE gear grades (e.g. 75W-90) use a different viscosity range. The two systems do not directly correspond.

How does temperature affect viscosity?

Oil viscosity decreases as temperature increases. The ISO VG system specifies viscosity at 40°C. The rate of 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+.

cSt stands for centistokes (mm²/s), the unit of kinematic viscosity. It measures how fast a fluid flows under gravity. 1 cSt = 1 mm²/s. Dynamic viscosity in cP (centipoise) = kinematic viscosity in cSt × density in g/cm³.

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.

ISO 3448 VG 2 – VG 1500 cSt @ 40 °C

Viscosity at 40 °C (cSt = mm²/s)

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ISO VG Class

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Viscosity Range (min – max)

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Midpoint Viscosity

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Typical Application

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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.

Range = Midpoint × 0.9 to Midpoint × 1.1 [cSt at 40 °C]

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.