Take a longer string or a longer stripe from paper. Put your hand with slinky thumb levelly on the desk and measure the circumference of the hand at the broad place. Put in addition the string or the paper completely around the hand (must narrowly lie close) and measure with a ruler. Also more simply with a measure volume.
Important hint
The declared dimensions are calculated for a very close seat. If you like it, nevertheless, rather very tightly, then order a size smaller. Nevertheless, the decleration of the dimensions is without guarantee.
