bootstrap lg

width 1200 px or greater
large desktop

bootstrap md

width 992 px to 1199 px
small desktop
iPad Landscape (1024px)

bootstrap sm

width 768 px to 991 px
iPad Portrait (768px)

bootstrap xs

width 767 px or less

@media max-width 667px

iPhone 6 & 6 plus landscape (667px)

@media max-width 568px

iPhone 5s landscape (568px)

@media max-width 375px

iPhone 6 & 6 plus portrait (375px)

@media max-width 320px

iPhone 5s portrait (320px)