Here is a simple step to follow if you don't already know the size of your wrist.
We recommend using a tape measure, but if you don't have one, use a small piece of tape or a cord. Wrap it around your wrist and measure the length against a ruler.
For a better comfort, we recommend to add 1cm / 0.4inc
Feel free to ask for a custom size, we will be happy to help you at no extra cost.