What do the different engine oil grades mean?

Can anyone help me understand the difference between different grades of engine oil (e.g. 10W-30, 5W-20, etc.) and which one is best for my Audi A3?

The numbers in engine oil grades represent the viscosity or thickness of the oil. Generally, lower numbers are better for colder climates and higher numbers are better for hotter climates. Check your owner's manual, as it should recommend a grade for your Audi A3 based on your location.

I've found that most auto parts stores have a chart or database that can tell you the recommended engine oil grade for your specific car make and model. Just give them your year, make, and model and they should be able to give you the right information.

It's always best to stick with the manufacturer's recommended engine oil grade for your car. Using the wrong grade can affect your car's performance and potentially cause damage. Check your owner's manual for the recommended grade and make sure to use that for your Audi A3.