ISO VG Viscosity Chart

What it is

ISO VG is the viscosity grade system for industrial oils, set by ISO 3448. The grade number is the oil's midpoint kinematic viscosity in centistokes (cSt, mm²/s) at 40 °C. Each grade allows plus or minus 10% around the midpoint. Each grade is about 50% thicker than the one below it, so there are no overlaps between grades.

How to read it

• Find the ISO VG on the label or data sheet, such as "ISO VG 220."
• The number is viscosity at 40 °C only. Viscosity at running temperature depends on the oil's viscosity index (VI).
• Select the grade from the equipment maker's recommendation, or from the viscosity the bearing or gear needs at operating temperature.

Viscosity grade chart

ISO 3448 continues to VG 2200 and VG 3200.

Key points

• Common grades: 32 to 68 for hydraulics and many compressors; 68 to 150 for circulating oils; 150 to 460 for enclosed gear drives; 460 to 680 and up for worm gears and slow, heavy gears. These are examples, not selections.
• A grade that is too thin lets surfaces touch and wear. A grade that is too thick runs hot and wastes power.
• Mixing grades gives a viscosity in between. Mixing different additive packages may cause problems.
• ISO VG does not convert directly to SAE grades. Use an equivalents chart only as a rough guide.

Common mistakes

• Treating ISO VG 46 like SAE "weight."
• Substituting the next grade up or down without checking the equipment needs.
• Ignoring the VI when equipment runs over a wide temperature range.

Governing standards: ISO 3448 (viscosity classification of industrial liquid lubricants); ASTM D2422 (US equivalent); ASTM D445 (kinematic viscosity test).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.