Test it on the Clean channel. Fender measures it as 25 decibel then a passive Strat. Thats what what they call 25 Db boost. If you want to believe in their made up figures you are free to do so, but when I see its 56-58 decibel louder without boost and 70 to 72 decibels louder with mid boost according to Fenders way of maning it its 56-58 Db boost without the mid boost engaged. With the midboost thats 70-72 Db boost. And quite Franklly a guitar thats active with active electronics is about 30 decibel louder than a passive guitar. And that guitar just has 1 boost. The Clapton signature Stratocaster has 4 boosts. So 70 Db boost as I measured both in volume and in the active cuircuit is correct. Those that buy the Clapton mid boost kit is loosing out on power. The same for those that buy The Cara Clapton pedal. Both has 45 decibels more than a passive Strat ( both I measured and looked into the active cuircuit), they only go to 45 Db boost because they just have 2 boosts. The Clapton signature Stratocaster because of its 4 boosts has more than 70db boost. But dont take my Word for it put The Clapton signature Stratocaster vs a passive Strat but in the Clean channel. The output of The Clapton signature Stratocaster is way way way too much for the distorted channel. But on the Clean channel you will get 70 decibels more. But remember that mean that you have a 181 times louder ( for the human ear ) then the other. I would not under any curcumstances take Fenders figures because they are made up to sell guitars.
dB's don't always mean the volume you hear in your ears. What you're thinking of is called 'perceived loudness'. We can hear different frequencies louder than other frequencies, even if they're the same dB level. That's a whole different topic in itself, but you can think of it like this-
IE- if someone pointed a speaker at you that blasted a frequency of 100hz at 75dB at you, it would be much quieter than someone blasting a frequency of 1000hz at 75dB. The lower you go in frequency, the lower the perceived volume generally is.
Or another example closer to how it relates to this- when a engineer is mixing a song in the studio and they need the guitars louder, often times instead of turning the volume up, they'll find an EQ area to raise, usually around 1.5kHz, because boosting that frequency on distorted guitars makes them jump out of the speakers more than turning the actual volume knob up does, due to the way we hear frequencies differently. The Clapton mid boost does exactly that, just a different frequency.
In the context of the Clapton boost, it's a 25dB boost of 500hz, right in the middle of any EQ. It looks like this-
So only the frequency right around 500hz is getting boosted by 25dB, not the whole volume of the guitar. What this ends up doing more is pushing the front end of an amp and gets a bit more dirt out of it. Clapton liked it because it felt like it was adding some compression and actually referred to it to Fender as a compressor. 500hz won't do a lot for the perceived volume you're thinking of, depending on which amp you're playing out of, it could either get a teeny bit louder or it'll just get more distorted.
The EMG SPC boost does something very similar, though I don't know the specific frequency range it boost. It does a great job at making a single coil sound like a humbucker.