Oil Viscosity Conversion Chart | ISO VG, AGMA & SAE

Technician pouring oil into a mechanical component

Oil Viscosity Chart & Conversion Guide

ISO, AGMA, and SAE Explained

Choosing the correct lubricant is one of the most important factors in protecting equipment and maintaining reliable operation. Whether you’re maintaining industrial gearboxes, hydraulic systems, or fleet vehicles, understanding oil viscosity is essential for ensuring machinery performs as intended.

One challenge many technicians and maintenance managers encounter is that viscosity can be expressed in multiple grading systems, including ISO VG, AGMA, and SAE. Because these standards were developed for different industries, converting between them isn’t always intuitive.

This guide includes an oil viscosity conversion chart that compares ISO VG, AGMA, and SAE viscosity grades, helping maintenance professionals quickly identify the correct lubricant for industrial equipment. It also explains how oil viscosity works, why multiple grading systems exist, and which lubricants are commonly used within each viscosity range.

What Is Oil Viscosity?

Oil viscosity describes a lubricant’s resistance to flow. One of the most common questions maintenance professionals ask is, "What does oil viscosity mean?" or "What does ISO VG mean?" Oil viscosity determines how easily a lubricant flows while ISO VG classifies industrial oils by their viscosity at 40°C. In practical terms, viscosity determines how easily an oil moves and how effectively it forms a protective film between moving components.

Thinner oils with lower viscosity flow more easily and are often used in systems that require quick circulation, such as hydraulic equipment. Thicker oils with higher viscosity flow more slowly and are designed to maintain a protective film under heavier loads or slower-moving mechanical systems.

Selecting the correct viscosity is critical because it directly affects lubrication performance. If the oil is too thin, it may fail to maintain a protective film, leading to increased wear. If it is too thick, it may not circulate properly, which can cause overheating or reduced efficiency.

Different types of equipment are designed to operate within specific viscosity ranges. For example, Many hydraulic systems use ISO VG 32 hydraulic oil or ISO VG 46 hydraulic oil, while industrial gearboxes often require heavier lubricants such as ISO VG 220 gear oil or ISO VG 460 gear oil. Selecting the correct ISO viscosity grade helps maintain lubrication performance while protecting equipment from unnecessary wear. Industrial gearboxes often require heavier lubricants such as ISO VG 220 or ISO VG 460.

At Keller-Heartt, these viscosity ranges are commonly found across several lubricant categories, including industrial gear oils, hydraulic oils, compressor oils, and food-grade lubricants used in processing environments. Understanding viscosity ratings helps ensure you select the appropriate lubricant for each application.

Why Multiple Oil Viscosity Standards Exist

Because lubrication requirements vary widely between industries, different organizations developed viscosity classification systems tailored to their equipment and operating conditions. Many maintenance teams search for an ISO VG conversion chart, AGMA viscosity chart, or SAE oil viscosity chart when replacing lubricants specified under a different grading system.

The most widely used standards today include the following.

Standard	Primary Industry Use
ISO VG	Industrial lubricants and hydraulic oils
AGMA	Industrial gear lubrication
SAE Crankcase	Automotive engine oils
SAE Gear	Automotive gear oils and differentials

Each system measures viscosity differently or defines grades based on performance requirements for specific equipment types.

The ISO viscosity grading system, developed by the International Organization for Standardization, was designed primarily for industrial lubrication. It classifies oils according to their kinematic viscosity at 40°C, providing a simple and consistent way to compare lubricants used in manufacturing equipment.

The AGMA system, created by the American Gear Manufacturers Association, focuses specifically on industrial gear protection. These grades correspond to viscosity ranges that perform well under the heavy loads and sliding contact typical of gear systems.

The SAE scale, developed by the Society of Automotive Engineers, serves the automotive industry. Separate grading systems exist for engine oils and gear oils, which is why the numbers used in automotive gear lubricants may appear much higher than those used in engine oils.

Because equipment manufacturers reference different systems, technicians often rely on viscosity conversion charts to identify equivalent oils when selecting or replacing lubricants.

ISO VG Explained (Industrial Oil Viscosity Grades)

ISO VG (ISO Viscosity Grade) is the most widely used industrial lubricant classification system. Maintenance professionals often use an ISO VG chart or ISO viscosity chart to compare lubricants used in hydraulic systems, industrial gearboxes, air compressors, and manufacturing equipment.

For example, an oil labeled ISO VG 220 has a viscosity close to 220 centistokes at 40°C.

The ISO grading system covers a wide range of viscosities used in industrial applications.

ISO Grade	Typical Applications
ISO VG 32	Hydraulic systems
ISO VG 46	Hydraulic & circulation oils
ISO VG 68	Bearings and light gearboxes
ISO VG 100	Compressors and industrial systems
ISO VG 220	Industrial gear oils
ISO VG 460	Heavy-duty gearboxes

These oils are commonly used throughout manufacturing environments, where proper lubrication ensures equipment reliability and reduces downtime.

Some of the most common lubricant searches include:

ISO VG 32 hydraulic oil
ISO VG 46 hydraulic oil
ISO VG 68 compressor oil
ISO VG 100 circulating oil
ISO VG 220 gear oil
ISO VG 460 gear oil

These viscosity grades are commonly used throughout industrial manufacturing, power generation, food processing, mining, and heavy equipment applications.

Many industrial lubricants supplied by Keller-Heartt follow ISO viscosity standards. Products such as industrial gear oils, compressor oils, hydraulic fluids, and food-grade lubricants are typically formulated within specific ISO VG ranges to meet equipment requirements.

Understanding ISO viscosity grades is often the first step in selecting the correct lubricant for industrial machinery.

AGMA Gear Oil Grades

While ISO VG provides a universal standard for industrial lubricants, the AGMA grading system focuses specifically on gear lubrication. Gear systems operate under heavy loads and significant sliding contact, which requires lubricants capable of maintaining a stable film between gear teeth.

Maintenance professionals frequently use an AGMA viscosity chart or AGMA gear oil equivalent chart when selecting replacement lubricants for industrial gear drives and enclosed gearboxes. AGMA grades correspond to viscosity ranges that provide effective protection for these demanding conditions.

Industry	Operational Challenges Solved	Core Fluids & Shop Supplies Housed
Trucking & Fleet Operations	Sustains heavy-duty engine uptime, supports demanding loads, and mitigates cold-weather regional complications.	High-performance diesel engine oils, DEF, fuel supplements, antifreeze/coolants, brake cleaners, degreasers, spill kits, and other fleet maintenance essentials.
Automotive Repair Shops	Supports rapid bay turnaround times and consistent premium service for small- to mid-size local garages.	High-volume motor oils (including TRUEGARD synthetic blends), brake cleaners, coolants, and transmission fluids.
Machine Shops & Metalworking	Maximizes machining precision, controls extreme operational heat, and significantly extends the life of expensive tools.	Professional-strength cutting oils, soluble oils, semi-synthetic coolants, and machine tool slideway lubricants.
Food & Beverage Manufacturing	Guarantees complete safety and regulatory compliance in high-temperature or extreme-cold environments.	NSF H1 and ISO 21469 certified food-grade lubricants, Cassida fluids, and inhibited propylene glycol heat transfer fluids.
Industrial Manufacturing	Defends critical equipment components against thermal breakdown, oxidation, and severe system wear over time.	Premium anti-wear hydraulic oils, industrial gear oils, multi-purpose greases, and safety degreasing solvents.

Industrial gearboxes used in manufacturing, mining, material handling, and processing equipment frequently rely on these viscosity ranges.

For example, AGMA 5 (approximately ISO VG 220) is a common choice for industrial gear drives operating under moderate to heavy loads. Higher grades such as AGMA 6 or AGMA 7 are often used in larger gearboxes where higher film strength is required.

Keller-Heartt supplies gear lubricants designed to meet these specifications, including products used in industrial gear drives, conveyors, and heavy machinery.

SAE Crankcase vs SAE Gear Oil

The SAE viscosity classification system is widely used in the automotive industry, but it includes two separate grading systems.

SAE System	Application
SAE Crankcase	Automotive engine oils
SAE Gear	Gear oils and differentials

One of the most common maintenance questions is "Is SAE 90 the same as ISO VG 220?" or "What is the SAE equivalent of ISO VG 320?" Although the numbering appears different, the viscosity of many gear oils is comparable across grading systems.

For example, SAE 90 gear oil is roughly equivalent in viscosity to ISO VG 220, even though the numbers look very different. This difference exists because the SAE gear oil scale was developed independently from the engine oil classification system.

SAE gear oils are commonly used in applications such as:

Automotive differentials
Truck transmissions
Fleet maintenance equipment

Keller-Heartt supplies lubricants used in many of these applications, particularly for fleet maintenance, automotive service, and heavy-duty machinery.

Oil Viscosity Conversion Chart (ISO VG, AGMA & SAE)

Equipment manufacturers reference different viscosity grading systems, which is why maintenance professionals frequently search for an oil viscosity conversion chart, ISO VG to SAE conversion, or AGMA to ISO viscosity chart when selecting replacement lubricants.

A viscosity conversion chart provides a quick way to identify approximate equivalents between ISO, AGMA, and SAE grades.

ISO VG	AGMA	SAE Gear
68	AGMA 2	—
100	AGMA 3	—
150	AGMA 4	—
220	AGMA 5	SAE 90
320	AGMA 6	SAE 140
460	AGMA 7	SAE 140+

Common Oil Viscosity Conversions

Some of the most frequently referenced viscosity conversions include:

ISO VG 220 to SAE 90
ISO VG 320 to SAE 140
ISO VG 460 equivalent
AGMA 5 equivalent
AGMA 6 equivalent
SAE 90 to ISO VG
SAE 140 to ISO VG

Always verify the lubricant specifications recommended by your equipment manufacturer before selecting an equivalent product.

These conversions are particularly useful when:

Replacing lubricants in existing equipment
Cross-referencing manufacturer recommendations
Identifying equivalent products between suppliers

Using a chart like the one above helps ensure technicians select lubricants that maintain the proper viscosity range required for reliable operation.

Download the Full Oil Viscosity Conversion Chart

If you frequently work with industrial lubricants, having an oil viscosity conversion chart, ISO VG chart, or AGMA viscosity chart readily available can make lubricant selection faster and more accurate.

The full chart compares several common viscosity systems, including:

ISO viscosity grades
AGMA gear oil classifications
SAE crankcase and gear oils
Saybolt viscosity measurements

Keeping a reference chart available can help maintenance teams quickly identify the appropriate lubricant for specific equipment requirements.

Choosing the Right Industrial Lubricant

While viscosity is one of the most important factors when selecting a lubricant, it is not the only consideration. Operating temperature, load conditions, and industry regulations all influence which lubricant will perform best in a given application.

For example, food processing equipment often requires NSF H1 food-grade lubricants, while heavy industrial gearboxes may require specialized additives for extreme pressure protection.

Keller-Heartt supplies a wide range of lubricants designed for these applications, including:

By selecting the proper viscosity grade and lubricant formulation, maintenance teams can help ensure equipment operates efficiently and reliably.

What does ISO VG mean?

ISO VG stands for ISO Viscosity Grade and classifies industrial lubricants according to their viscosity at 40°C.

What is an oil viscosity conversion chart?

An oil viscosity conversion chart compares ISO VG, AGMA, and SAE viscosity grades to help identify equivalent lubricant viscosities across different industries.

Is SAE 90 the same as ISO VG 220?

While the grading systems differ, SAE 90 gear oil is approximately equivalent in viscosity to ISO VG 220.

How do I choose the correct oil viscosity?

Always follow the equipment manufacturer's recommendations and consider operating temperature, load, speed, and lubricant specifications when selecting a viscosity grade.