Sound and Noise Meter

The decibel (dB) is a logarithmic unit used to express the ratio of two values of a physical quantity. One of these values is often a standard reference value, in which case the decibel is used to express the level[a] of the other value relative to this reference.

The Sound Pressure Level (SPL) measurement application measures the sound level in decibels (dB) using your built-in microphone and shows a reference.

Many smartphone microphones are designed for human voice (300-3400Hz, 40-60dB). Voice calls do not require high-performance microphones.
For this reason, the maximum value is limited by the manufacturer and very loud sounds (100+ dB) can not be detected. Moto G3 (max. 80), Galaxy S6 (85dB), Nexus 5 (82dB), HTC Desire (82dB) ...