Väisänen Design uses the inside diameter for ring sizes.
There is no widely used worldwide standard for ring sizes, and sizing systems vary from country to country, although there is an ISO standard for ring sizes (ISO 8653:2016). Based on the ISO standard, in most European countries ring sizes are specified either using the internal circumference in mm or inside diameter in mm.
If you don’t know your size but you have a ring that is the right size for you, you can measure the diameter in mm directly from the ring – this is your size. If you don’t have a ring, you can wrap a paper strip around your finger and measure this way the inside circumference. With this value you can see the right size in diameter from our chart.