This is the sizing information provided by HSGI:
"Sizing is important! Please read instructions below carefully!
1. Choose the size of plate carrier pockets:
Users with ESAPI plates 10" x 12" (Medium) or smaller should order the medium SPC.
Users with ESAPI plates 11" x 13" (Large) or greater should order the large SPC. 11” x 14” (X-Large) plates are accommodated, but corners at the bottom are visible.
2. Choose the size of the Sure-Grip Padded Belt®. Because the belt rides a bit higher than when worn separately , this balances out the extra circumference created by the plate pockets and makes the sizing work very much like the sizing if being worn on your hips. But GENERALLY, here is a good place to start.
Take a cloth tape measure and measure around your stomach near the belly button, then use the table below...
<32" - order a 30.5" Sure-Grip Padded Belt®
33" to 38" - order a 35.5" Sure-Grip Padded Belt®
39" to 44" - order a 41.5" Sure-Grip Padded Belt®
>45" - order a 46" Sure-Grip Padded Belt®"