Viscosity Converter (ISO VG ↔ SAE ↔ cSt)
Match industrial oil grades across ISO, SAE engine, SAE gear
ISO VG, SAE motor oil, SAE gear oil के beech conversion
Industrial lubricants are specified in three different standards: ISO VG (Viscosity Grade, used for hydraulic and gear oils), SAE motor oil (0W, 5W, 10W, 20, 30, 40, 50), and SAE gear oil (75W, 80W, 90, 140). All three describe the same physical property — kinematic viscosity in centistokes (cSt) — just with different labels optimised for different applications. ISO VG uses the cSt value at 40°C directly as its grade number: ISO VG 46 = 46 cSt at 40°C. SAE 30 motor oil spans roughly ISO VG 100 (≈100 cSt at 40°C); SAE 90 gear oil spans roughly ISO VG 150. A hydraulic system spec of 'ISO VG 46' needs an oil measuring 46 ± 4.6 cSt at 40°C — a SAE 20W motor oil is close but not exact. This converter matches ISO VG 10 through ISO VG 1500 to their SAE equivalents and cSt values.
Calculator
Typical use: Industrial hydraulics (common). The SAE motor/gear cross-references are approximate — SAE grades also include cold-flow requirements that ISO VG does not define. Always verify against the equipment manufacturer recommendation.
ƒFormula
ISO VG number = kinematic viscosity (cSt) @ 40°C ±10%ISO VG is defined as the nominal kinematic viscosity in cSt at 40°C. An ISO VG 46 oil measures between 41.4 and 50.6 cSt at 40°C (nominal ±10%). SAE motor oil grades map approximately — SAE 10W ≈ VG 22, SAE 30 ≈ VG 100, SAE 40 ≈ VG 150. There is no exact formula converting SAE to ISO because SAE specs also include cold-flow requirements (the 'W' winter grades).
Units: Viscosity: centistokes (cSt) = mm²/s · Temperature: °C
Oil viscosity — ISO VG, SAE, cSt mein kya difference?
Industrial lubricants teen alag-alag standards mein specify hote hain: ISO VG (hydraulic + gear oils), SAE motor oil (engine oils), aur SAE gear oil. Actually teeno same property describe karte hain — kinematic viscosity at 40°C in centistokes (cSt). Sirf naming convention alag hai. ISO VG 46 ka matlab oil 46 cSt hai @ 40°C. SAE 30 motor oil roughly ISO VG 100. SAE 90 gear oil ≈ ISO VG 150. Pneumatic compressor usually ISO VG 32 chahta hai; hydraulic system ISO VG 46 ya 68; gearbox ISO VG 150 se 320.
Worked Examples
Matching hydraulic oil across suppliers
Problem: Your machine manual calls for ISO VG 46 hydraulic oil. Supplier quotes 'HYD-20'. What is that?
Solution: 'HYD-20' is generic marketing — the actual spec on the bottle should say ISO VG 46 or cSt at 40°C. Ask for the kinematic viscosity value at 40°C — target 46 ± 4.6 cSt. A SAE 20W motor oil is ~50 cSt so it's functionally close, but use purpose-made hydraulic fluid for long-term reliability.
Compressor oil selection
Problem: Atlas Copco screw compressor manual says 'Use ISO VG 46 PAO synthetic'. Equivalent SAE?
Solution: ISO VG 46 ≈ SAE 15W (roughly). But for screw compressors use ONLY the specified synthetic PAO — mineral SAE 15W will carbon up at compressor discharge temperatures (90–110°C) much faster than PAO synthetic.
Gear oil confusion
Problem: Gearbox data sheet says 'SAE 90' or 'ISO VG 150'. Are these the same?
Solution: Approximately yes. SAE 90 gear oil is typically 140–220 cSt at 40°C, which spans ISO VG 150 (135–165) to ISO VG 220 (198–242). Most mineral SAE 90 gear oils fall around ISO VG 150. For EP gearboxes, also check the GL-4 or GL-5 additive grade.
Viscosity Cross-Reference — ISO VG, SAE Motor, SAE Gear, cSt @ 40°C
| ISO VG | cSt @ 40°C | SAE Motor | SAE Gear | Typical Use |
|---|---|---|---|---|
| VG 10 | 9 – 11 | — | — | Spindle oil, fine machinery |
| VG 22 | 20 – 24 | SAE 5W | — | Light hydraulics, refrigeration |
| VG 32 | 29 – 35 | SAE 10W | — | Air compressors, most hydraulics |
| VG 46 | 41 – 51 | SAE 15W | SAE 75W | Industrial hydraulics (most common) |
| VG 68 | 61 – 75 | SAE 20 | SAE 80W | High-pressure hydraulics, bearings |
| VG 100 | 90 – 110 | SAE 30 | SAE 80W-90 | Circulation, light gearboxes |
| VG 150 | 135 – 165 | SAE 40 | SAE 90 | Industrial gearboxes (most common) |
| VG 220 | 198 – 242 | SAE 50 | SAE 90 heavy | Heavy gearbox, slow-speed |
| VG 320 | 288 – 352 | — | SAE 140 | Heavy-load worm gears |
| VG 460 | 414 – 506 | — | SAE 140 | Very slow, very heavy gearboxes |
| VG 680 | 612 – 748 | — | SAE 250 | Open gears, chain drives |
| VG 1000 | 900 – 1100 | — | — | Specialty, heaviest open gears |
SAE motor and gear oil cross-references are approximate — SAE specs also include cold-flow (winter W) requirements not captured by ISO VG. For exact specification always follow the equipment manufacturer's recommendation.
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