Sound Pressure Level (dB SPL) Converter
Convert sound pressure between pascals and decibels (dB SPL in air, dB re 1 µPa in water), with millipascals and micropascals.
Convert sound pressure level (db spl)
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Sound Pressure Level (dB SPL) units
Every unit below converts to every other one in the calculator. Values are relative to the base unit, the pascal (Pa).
| Unit | Symbol | System | Value |
|---|---|---|---|
| Pascal | Pa | SI | Base unit |
| Millipascal | mPa | SI | = 0.001 Pa |
| Micropascal | µPa | SI | = 0.000001 Pa |
| Decibel SPL (re 20 µPa) | dB SPL | other | Pa = 0.00002 × 10^(dB SPL ÷ 20) |
| Decibel re 1 µPa (underwater) | dB re 1 µPa | other | Pa = 0.000001 × 10^(dB re 1 µPa ÷ 20) |
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About sound pressure level (db spl) units
Sound pressure is the small, rapid change in air pressure that makes a sound. It is measured in pascals (Pa), but because human hearing covers a range of about a million to one, sound is almost always quoted as a level in decibels. The sound pressure level is 20 times the base-10 logarithm of the pressure divided by a reference pressure.
In air the reference is 20 µPa, about the quietest sound a young adult can hear, so 0 dB SPL equals 20 µPa. Every 20 dB multiplies the pressure by 10: 20 dB SPL is 200 µPa and 120 dB SPL is 20 Pa. In water and other media the reference is 1 µPa, so the same pressure reads about 26 dB higher. A sound level meter set to dBA applies a frequency weighting, so a dBA reading is not a pure pressure level and is not converted here.
Frequently asked questions
- How many pascals is 94 dB SPL?
- 94 dB SPL is about 1 pascal (1.002 Pa). That is why acoustic calibrators for microphones commonly produce 94 dB at 1 kHz.
- Why is the decibel formula 20 log and not 10 log?
- Sound power is proportional to the square of the pressure. A level in decibels is defined from power with 10 log, so for pressure it becomes 20 log. Doubling the pressure adds about 6 dB, doubling the power adds about 3 dB.
- Why does underwater sound use a different reference?
- Standards set the reference pressure at 20 µPa in air and 1 µPa in water. The two scales are 26.02 dB apart for the same pressure, so a level in dB re 1 µPa must never be compared with one in dB SPL without converting it.
- Can zero pascals be converted to decibels?
- No. A level in decibels is a logarithm, and the logarithm of zero is undefined. Silence has no level on this scale; the calculator asks for an amount greater than zero.