@Punch Short answer: no. Long answer: It’s complicated and inconsistent. There’s a link at The Base Camp (UK) that shows the tank capacity of common Optimus and Primus stoves. But No. 1 for instance refers to a roarer burner stove, and No.5 is the silent version of the same sized stove. Tony
In the beginning most producers started on model No1 and that used to be a clone of the first Primus born in 1892 and numbered 1 some years later, next step by many companies was to double the size to No2 and double again to No3 and a No0 that was smaller than No1. No5 and 6 use to be 1 and 2 size with silent burner. Other numbers use to be less similar between the producers and sometimes old numbers are put on new designs and old ones get new numbers. This old type of wick stove seem to have logic but inofficial numbers - 1, 2 or 4 in bottom plate for the number of wicks.
An Optimus 45 is the same size and configuration as a Svea 106, etc. etc. They are by and large arbitrary numbers assigned by various manufacturers. That said, a 1 will often be a 2-pint fixed-leg domestic with a roarer burner, with a 5 being the same stove with a silent burner.
