Spanish twin bed: 0.90 m
US twin bed: 1.00 m

Spanish "two twin beds": 1.80 m
US king-size bed: 2.00 m

A Spanish "habitación doble" usually means two twin beds. You will find them separetely in hostals and pushed together in hotels.

Spanish "cama de matrimonio" (before): 1.35 m
Spanish "cama de matrimonio" (now): 1.50 m
US queen bed: 1.55 m

Note that the "new" size of Spanish "cama de matrimonio" is quite common at private homes, but not at hostals, mainly for the lack of space. Therefore, if you book a room with "cama de matrimonio" you'll likely to get a 1.35 m wide bed.