I'm curious. What is your "normal" listening volume?

The Center for Disease Control (CDC) provides a free sound level meter app for both Apple and Android phones. This app is calibrated for levels set by the National Institute of Occupational Safety and Health:

NIOSH Sound Level Meter App | Noise and Hearing Loss | CDC

The NIOSH Sound Level Meter and several other apps can be downloaded from your device's App Store by simply typing NIOSH into the search box. 

Warning: at the rate that federal agencies seem to be disappearing I wouldn't wait long to do this. 

For Dynaudio loudspeaker owners Dynaudio provides several free apps, including a sound level meter, that can be downloaded from your phone's app store. Simply type Dynaudio into your App Store search box and a list of free apps will appear. 

Some method of generating a steady state tone at multiple set frequencies will be important and there are a number of CD's and downloads available for this, some free and some costing small amounts.

I own and have compared the above two tools and there might be minor response variances between them in your use.

What's important though is to use any sound level diagnostic device, including calibrated microphones and software of course, to measure and establish a baseline for future comparisons.

When testing or changing any ear or room acoustics having a set of baseline measurements recorded can be invaluable for detection and/or confirmation of differences that might or might not be audible.

Ugh! The last sentence above should read:  When testing or changing any gear or room acoustics....

Calm levels (30%): 65-75dB peaks

Regular (60%): 83-90dB peaks

Stadium Levels (10%): 95-110dB peaks

For many, people will either listen louder or softer because their systems render tonality differently at different volumes (e.g. a tube preamp's volume will can determine the amount of "tubey-ness" and often sounds better starting at 11 o'clock"). But for really great systems, tonality, coherence, and realism are retained regardless of the system.

@ ditusa, thanks!  Cool app. 
 

70-82 db. My apt is noisy, so less than that is little more than background.  The ambient noise level affects how loud your music needs to be played, as well as its dynamic range.  

Sorry @sargonicuse, thanks for the link!