Motor oil viscosity grades
What do the numbers on an oil bottle mean? Each grade below is decoded in plain English — the cold-start (winter) rating, the hot-temperature thickness, and which engines specify it. Remember: viscosity is not the same as your engine's required specification.
See every grade side by side on the oil viscosity chart →
Use this section for grade meaning, not approval matching
Grade pages 13 Each page explains one SAE viscosity grade.
Cold ratings 0W, 5W, 10W, 15W, 20W The W number describes cold-start flow.
Hot ratings 8, 16, 20, 30, 40, 50 The second number describes hot operating thickness.
- 0W-8 0W-8 explained — an ultra-thin grade for recent hybrids and economy engines, used only where specifically specified for fuel-economy targets.
- 0W-16 0W-16 explained — what the 0W and 16 numbers mean, and why this very thin, ultra-economy grade should only be used where it is specifically specified.
- 0W-20 0W-20 explained — what the 0W and 20 numbers mean, why so many modern engines specify it, and what the thin grade is and is not good for.
- 0W-30 0W-30 explained — excellent cold-start flow with a mid-weight 30 hot film, common in many modern European and gasoline engines.
- 0W-40 0W-40 explained — excellent cold-start flow with a thicker 40-weight hot film, common in European and performance engines.
- 5W-20 5W-20 explained — what the 5W and 20 numbers mean, and why this thin, fuel-economy-friendly grade is specified for many modern gasoline engines.
- 5W-30 5W-30 explained in plain English — what the 5W and 30 numbers mean, cold and hot behavior, and which engines commonly call for it.
- 5W-40 5W-40 explained — what the 5W and 40 numbers mean, and why this grade is common in many European, turbocharged, and diesel applications.
- 5W-50 5W-50 explained — good cold-start flow with a thick 50-weight hot film, used in some high-output, performance, and track engines where specified.
- 10W-30 10W-30 explained — what the 10W and 30 numbers mean, and which engines commonly use this middle-of-the-road, milder-winter grade.
- 10W-40 10W-40 explained — what the 10W and 40 numbers mean, and which engines commonly use this thicker, warm-weather-friendly grade.
- 15W-40 15W-40 explained — what the 15W and 40 numbers mean, and why this grade is common in diesel, heavy-duty, and hot-climate use.
- 20W-50 20W-50 explained — what the 20W and 50 numbers mean, and why this thick grade is associated with classic, air-cooled, high-performance, and very hot-climate use.