I would like to know how to tell engine size of a BMW.
I only buy cars a 1.9 litre or smaller engine.
With BMW's it used to be that the last two numbers represented the engine size. Sadly on newer cars this seems to have been abandoned so it is no longer a valid way to tell. You'll have to do some research based not only on the model but also the year the car was manufactured. This information is generally available in publications such as Parkers or Glasses Guide in the UK. I'm sure there will be equivalent publications available locally or online.