Sound level meters measure sound in units called “decibels of sound pressure level” and is abbreviated dB SPL.​ The microphone on the sound level meter is able to measure the amplitude of the sound pressure wave. ​

0 dB SPL represents to the minimum detectable pressure by the average human ear which corresponds to 20µPa (µPa means micropascal; pascals are units of pressure). This is an extremely low pressure; it is less than a billionth of atmospheric pressure (which is the pressure of the air all around us). ​

Since the human ear can hear such a large range of amplitudes, decibels are calculated with a logarithmic scale where p=pressure and is always calculated as a ratio of 2 pressures (an observed or measured pressure p over a reference pressure p (the minimum detectable pressure by the average human ear which corresponds to 20µPa). The formula for calculating dB SPL is: ​​

• A sound that is 10 times greater in sound pressure would equate to an increase of 20 dB SPL.​
• A sound that is 10 times greater would measure 20 dB higher​.
• A sound that is 100 times greater would measure 40 dB higher​.

Don’t panic, you won’t have to calculate decibels to teach about Dangerous Decibels!