I have a very bogus but at least a crude approximation of how loud I’m listening with my headphones with the built-in iOS loudness feature https://imgur.com/a/Fbes920/

oh and do not trust your phone's built-in app, like my Samsung well-being app. If I plug in all the numbers of my IEM w a dongle DAC at max volume into a headphone calculator, it came out to @ 122db, while the app only shows 98db. BIG OOF, blindly trust it gonna make it worse

P/S: I posted this on the other sub, someone asked the same question

If you have FiiO BTR, Qudelix 5k or smth like that, then there is a convenient way - through a built in calculator in an app. Otherwise there's not.

HearAngel

Could you elaborate? I have the Q5

The volume on the Qudelix just tells me how much headroom I have left, like -15db.

Actually I was wrong about Qudelix, it is not that convenient there, because the app does not have a calculator. It only has the mV level on the right of the headroom regulator. For example you get 1e+2 there, 1e+2 is 100, so you get 100mV, means 0.1VRMS. https://www.headphonesty.com/headphone-power-calculator/ - you can calculate the else here.

I was wrong because FiiO devices really have this calculator built into the app and it's connected to the volume level, so you enter sensitivity and impedance of your headphones and get output power and DBFS in return. It's the most convenient way.

Cool, thank you