A 54″ × 72″ mattress / bed is  137cm × 183 cm in centimeters. In Australia: it’s almost as big as Double or Full (54 in × 74 in) In USA: it’s almost as big as Double or Full (54 in × 75 in) In UK: it’s almost as big as Double or Full (53
A 72″ X 78″ mattress / bed is  183 cm × 198 cm in centimeters. In Australia: it’s bigger than  Queen (60 in × 80 in), but smaller than King (72 in × 80 in). In USA: it’s bigger than Queen (60 in × 80 in), but smaller than King (76 in × 80 in).