May we discuss pots, please?

As a browse various sites for plants, I'm getting quite confused (easily done, I know).

Some give pot sizes e.g. 60-70cm pot

Some give sizes in litres e.g. 2ltr pot

Not quite sure how to decide on the size of the plant vs price when the description isn't consistant.

I've seen a black bamboo for what I think is a really good price, but the pot is in cm; makes it difficult to guage if its a bargain when trying to compare it with another site which has one sized in litres

Anyone able to help/clarify/have a chart?

TIA

 

This site gives SOME ltr to cm ratios.
http://www.plastic-plant-pots.co.uk/plant-pots.html