Related: Sound Tune: Pioneer’s Sound Tune app is a great way to bring the sound of high-end audio to a basic factory car stereo and speaker set.
This application in realtime shows current value of sound volume.
The main indicator shows current sound volume value and giving short explanation of it.
Also there is volume value timeline in the bottom part of screen.
This application has settings screen, which give ability calibrate decibels according to device microphone specifics.
Apple Watch application can measure sound volume without iPhone device.
Related: Decibel: dB sound level meter Audio noise Spectrum Analyzer