The modern Brannock device takes three measurements of each foot:
Foot and arch lengths correspond to numeric Brannock sizes, and foot widths correspond to letter Brannock widths AAAA (narrowest) to EEEE (widest), as follows:
Foot Length = 7 1 3 inches + ( Men's Brannock Size × 1 3 inch ) {\displaystyle {\text{Foot Length}}=7{\tfrac {1}{3}}{\text{ inches}}+({\text{Men's Brannock Size}}\times {\tfrac {1}{3}}{\text{ inch}})}
Arch Length = 5 18 50 inches + ( Men's Brannock Size × 11 50 inch ) {\displaystyle {\text{Arch Length}}=5{\tfrac {18}{50}}{\text{ inches}}+({\text{Men's Brannock Size}}\times {\tfrac {11}{50}}{\text{ inch}})}
Width = 1 10 16 inches + ( Men's Brannock Size × 1 8 inch ) + ( Steps Up From AAAA × 3 16 inch ) {\displaystyle {\text{Width}}=1{\tfrac {10}{16}}{\text{ inches}}+({\text{Men's Brannock Size}}\times {\tfrac {1}{8}}{\text{ inch}})+({\text{Steps Up From AAAA}}\times {\tfrac {3}{16}}{\text{ inch}})}
Women's Brannock sizes are offset from men's by one:
Women's Brannock Size = Men's Brannock Size + 1 {\displaystyle {\text{Women's Brannock Size}}={\text{Men's Brannock Size}}+1}
Aeppel, Timothy (10 January 2011). "Maker of Foot Measurer Tries to Stop Other Shoe From Dropping -- On It -- Iconic Bannock Device Hangs On By Its Toes Against Foreign-Made Rivals". United States: Wall Street Journal, Eastern edition. p. A.1. ↩
US patent 1682366, C. F. Brannock, "Foot-measuring instrument", published 28 Aug, 1928 https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=US1682366 ↩
US patent 1725334, "Foot-measuring instrument", published 1929-08-20 https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=US1725334 ↩
"From the Collections: Charles Brannock". Smithsonian Institution. May 21, 2014. https://invention.si.edu/collections-charles-brannock ↩
Hill, Benjamin. "Chiefs give Brannock Devices their due", MiLB.com, New York, 4 June 2018. Retrieved on 15 August 2019. https://www.milb.com/milb/news/promo-watch-syracuse-chiefs-salute-brannock-devices/c-279300928 ↩