Is there a 'golden rule' for understanding small plant pot sizes?

It is easy to understand the 1 litre size and larger.
I was looking at some square pots online today. 11cm is how they were described. Is it too difficult for manufactures to put the three dimensions of a 3 dimensional shape on the label?

What about small round pots? 7cm or 11cm? Are these the diameters of the top.
I have some pots that are the same width as a 9cm pot, but are about a 1/3 shorter. I don't know if they are also described as 9cm. They are a very handy size for what I do, and I would like to get some more. I'm not sure what the search criteria would be for these?
I was looking at some square pots online today. 11cm is how they were described. Is it too difficult for manufactures to put the three dimensions of a 3 dimensional shape on the label?

What about small round pots? 7cm or 11cm? Are these the diameters of the top.
I have some pots that are the same width as a 9cm pot, but are about a 1/3 shorter. I don't know if they are also described as 9cm. They are a very handy size for what I do, and I would like to get some more. I'm not sure what the search criteria would be for these?
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I posted a similar question a while ago and got some useful answers
The width of my hand measured at the knuckles is 4"/10cm - standard for measuring horses and handy for pot depths and width. Fingers' width and length of middle finger are also good guides for buying pots if I need to but usually, for moving seedlings from plug trays to small pots I just recycle the 5 to 7cm ones that came with small brassicas or bedding plants and when the plants are big enough to need moving on from those they can generally cope with being planted out. If not, next pot up which would be a 9cm jobby.
I will have to be satisfied by having a general idea about pot sizes.
Just as an observation, for some reason 9cm pots seem to be a popular size for online & postal retailers to send their plants in. 🌱🌞