SPL (sound pressure level) meter app uses your microphone to measure noise volume in decibels(db), and shows a reference.
We calibrated a lot of android devices using an actual sound meter with dB(A).

REMEMBER!! Most smart phone microphones were aligned to human voice (300-3400Hz, 40-60dB).
Therefore maximum value is LIMITED by manufacturers, and very loud sound(100+ dB) cannot be recognized. Moto G3 (max.80), Galaxy S6 (85dB), Nexus 5 (82dB), HTC Desire(82dB).
System Requirements:
Requirements: Android 6.0+

Home Page - https://play.google.com/store/apps/details?id=kr.aboy.sound&hl=en