Sound pressure level (SPL) is also called as acoustic pressure level. It is a logarithmic measure of sound level. Sound pressure is more typically expressed in decibels scale (dB) and denoted by the symbol Lp. The lowest sound pressure that can be heard by humans are approximately 2 10-5 Pa or 2 ten billionths of the atmosphere. Use our online calculator to calculate the Sound Pressure Level (SPL) by entering the sound pressure and reference pressure.