TECHNICAL GUIDE
Using Oil Viscosity Comparison Chart
Learn how ISO VG and SAE viscosity ratings compare and how to select the correct lubricant for your equipment.
Technical Guide • 5 min read
Comparing ISO VG (International Standards Organization Viscosity Grade) and SAE (Society of Automotive Engineers) viscosity grades can be done using a viscosity conversion chart. The process is straightforward: simply read the chart horizontally.
For instance, you’ll find that an SAE 50 motor oil aligns with a viscosity similar to that of an SAE 90 gear oil, an AGMA 5 gear lubricant, and an ISO 220 hydraulic fluid/gear lubricant. The chart also provides references to the corresponding kinematic viscosity and Saybolt viscosity values for added clarity.
For instance, you’ll find that an SAE 50 motor oil aligns with a viscosity similar to that of an SAE 90 gear oil, an AGMA 5 gear lubricant, and an ISO 220 hydraulic fluid/gear lubricant. The chart also provides references to the corresponding kinematic viscosity and Saybolt viscosity values for added clarity.
Understand the ISO VG System
ISO VG grades are based on the lubricant’s kinematic viscosity at 40°C (104°F). The number represents the oil’s viscosity in centistokes (cSt) at that temperature.
Understand the SAE System
SAE grades are more complex and often include both low-temperature (W for winter) and high-temperature viscosity values. For example, SAE 10W-30 means the oil has the viscosity of an SAE 10 oil at low temperatures and an SAE 30 oil at high temperatures.
Important Reminder
Keep in mind that these conversions are approximate, and actual performance can vary based on the oil’s composition and additives. It’s always a good practice to consult your equipment manufacturer’s recommendations and follow their guidance when selecting the right oil viscosity for your specific application.
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