Well, ROF is measured in more than one way. You've basically got four different types, so pick which one you like...
Cyclic Rate: This is the mechanical rate at which a gun can fire when the trigger is held on, disregarding stuff such as magazine capacity, mag changes, overheating etc. So despite the fact that the cyclic rate is usually expressed in RPM (rounds per minute), it does not mean that the gun in question could actually keep that rate of fire up for a minute.
Sustained Rate: This is what it says, i.e. the rate at which fire can be put out continuously over an extended period, taking into account things such as reloading, changing barrels (on things like an M60, for which the crew are provided with an asbestos - or similar - heat-resistant glove), replenishing water on a water cooled machine guns (there are records of Vickers MG gun crews urinating into the water jacket of their machine guns during prolonged engagements. In 1916, some Vickers MGs were fired almost continuously for ten hours apparently, necessitating multiple barrel changes and a lot of water, since the Vickers MG boils off about a pint and a half of water for every 1,000 rounds put through the thing.
Rapid fire rate: This is the 'ignore everything else, this is an emergency' rate of fire, which could not realistically be maintained on most guns, since it would likely damage them in some way.
Semi-automatic rate: This is the rate at which you can put rounds out using repeated single trigger pulls, disregarding mag changes and such, on guns with a low automatic cyclic rate, this figure is usually pretty close to the full auto rate assuming the firer can pull the trigger fast enough, and there are tricks such as 'bump-firing' (i.e. using the recoil to help pull the trigger again) which can make this figure misleading sometimes, since firing like that is unlikely to be very accurate.
As with most things, the 'brochure figures' are usually the fastest one the makers can quote, and not always the most practical guide, but usually quoted in order to give it the 'wow factor'. This is the same as when aircraft manufacturers say their fighter plane 'can do Mach 2' when what they don't mention is that it'll have to be in full afterburner to manage it, and will as a result run out of fuel in five minutes, so will probably then crash if it isn't near a suitable airfield lol.
Back with airsoft guns however, a decent chromo will tell you the ROF from a few shots, or you can time how long it takes to empty ten rounds and then take that up to a minute to give your a rough guide on ROF.