Seat Circumference : Lower torso garment measurement from 25 mm (1 in). above bottom of fly curve from folded edge to folded edge, multiplied by 2 to obtain circumference
NFPA 1977 Standard on Protective Clothing and Equipment for Wildland Fire Fighting, 2005 ed. http://www.nfpa.org/assets/files/aboutthecodes/197 7/1977_f2010_rop_ballot.pdf, (Std: Prot Clothing and Equip for Wildland Fr Fight - Amer) {431 NFC}