Below is a button that will take you to a website that has a printable template that you can use to measure your wrist. (Easier to size multiple people.) If you don't have access to a printer i have typed out instructions below as well.

Materials
Paper
Scissor
Ruler

Pencil/ Pen

Cut a strip from the paper.
(Any paper works fine. We are a size inclusive business so if you need two pieces of paper use tape or glue it will work the same) 

Wrap the piece of paper around your wrist and mark where the two pieces touch. Not too tight or too loose. 

Take the ruler and measure out from the end of the paper to the mark. The example above is 7 ½  . Put the size in the form when ordering and I will handle the rest.