It's worth finding out how much liquid fits in each type of glass for future
reference - this helps a lot if you're making up a drink from scratch and
don't want to under/over pour.
The "Martini" glasses I work with hold 5 Oz and our house martini is 3 Oz gin
(plus dry vermouth). When stirred with ice, water will dilute the drink and
add to the volume as well.