If you already own a belt, we recommend measuring your current belt on the tightest setting you use to give you the circumference of the belt at the setting you usually use.
If you do not have a belt then please measure your waist where the belt will sit (which is normally just above the navel), with your abdominal muscles braced. Please do not use your trouser waist measurement as this will not be accurate for the belt measurement.
We typically recommend a belt where you fall in the middle of the sizing guide, as this will allow you to adjust the belt in either direction depending on your preference of fit, what exercise you are using the belt for, should your bodyweight change, or if you wear the belt over layers of clothes or a neoprene belt.