We have found these two sizes fit 90% of users. Velocity System provides measurements on their website, but we find the cummerbunds to be highly adjustable to fit most users. If you find after purchase that you need a different size, please contact us.
The APC Main Carrier is available in two sizes corresponding to plate size; S/M and L/XL. The plate pockets are sized to accommodate most plate shapes and thicknesses. This includes SAPI/ESAPI cuts, with or without soft armor, and Shooter/Swimmer cuts, again either with or without soft armor. If using soft armor, only plate backers work. This does not fit any other profile soft armor.
The Standard MOLLE Plate Pocket Cummerbund (CBN3) is designed to accept 6"x 6" hard armor plates or side soft armor inserts. Thin plates (< 0.5" Thick) fit with no additional pieces. Thicker plates (> 0.55" Thick) will require additional retention. Velocity System provides measurements on their website, but we find the cummerbunds to be more forgiving and highly adjustable to fit most users. If you use their measurements, measure at the belly button.