Convert sound pressure units, and go between pascals and dB SPL.
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Sound pressure is the tiny rise and fall in air pressure that a sound wave causes. It is measured in pascals, and everyday sounds are a very small fraction of one pascal. Enter a value and pick the units. To work in decibels, use the formula below, since dB is a ratio on a logarithmic scale and not a pressure unit.
1 Pa = 10 dyn/cm² = 10 µbar exactly.
| Pascal (Pa) | Dyne/cm² |
|---|---|
| 0.00002 | 0.0002 |
| 0.0002 | 0.002 |
| 0.002 | 0.02 |
| 0.02 | 0.2 |
| 0.2 | 2 |
| 1 | 10 |
| 2 | 20 |
| 20 | 200 |
| 200 | 2,000 |
11 Pa → dB SPL
1 Pa = 93.9794 re 20 µPa
1 Pa = 93.9794 re 20 µPa
285 dB SPL → Pa
85 re 20 µPa = 0.355656 Pa
85 re 20 µPa = 0.355656 Pa
360 dB SPL → mPa
60 re 20 µPa = 20 mPa
60 re 20 µPa = 20 mPa
420 µPa → Pa
20 µPa = 0.00002 Pa
20 µPa = 0.00002 Pa
51 Pa → dyne/cm²
1 Pa = 10 Dyne/cm²
1 Pa = 10 Dyne/cm²
6100 dyne/cm² → Pa
100 Dyne/cm² = 10 Pa
100 Dyne/cm² = 10 Pa
PascalPa
The SI unit of pressure: 1 N/m². 20 µPa is the reference for 0 dB SPL in air.
MicropascalµPa
10⁻⁶ Pa. Used for the hearing reference and in underwater acoustics.
Microbarµbar
0.1 Pa exactly, the same as 1 dyn/cm². A CGS unit found in older data sheets.
dB SPLdB
A logarithmic level, not a pressure: 20 × log₁₀(p ÷ 20 µPa), using RMS pressure.
Sound pressure level compares a pressure with a reference of 20 µPa in air.
SPL = 20 × log₁₀(p ÷ 20 µPa)
p = 20 µPa × 10^(SPL ÷ 20)
So 1 Pa gives 20 × log₁₀(50,000) = 93.98 dB, which is why microphones are often calibrated at 94 dB. Going the other way, 60 dB gives 20 µPa × 1,000 = 0.02 Pa.
| dB SPL | Pressure (RMS) |
|---|---|
| 0 | 20 µPa |
| 30 | 632 µPa |
| 60 | 20 mPa |
| 85 | 0.356 Pa |
| 90 | 0.632 Pa |
| 94 | 1.00 Pa |
| 100 | 2 Pa |
| 120 | 20 Pa |
| 140 | 200 Pa |
Every extra 20 dB is ten times the pressure. Every extra 6 dB is about twice the pressure.
The level formula uses root-mean-square pressure. For a pure tone, the peak is 1.414 times the RMS value, so a 94 dB sine wave swings to ±1.41 Pa. Check which one your instrument reports before you compare numbers. Real sounds such as impacts can have a far higher peak than this ratio suggests.
These come straight from the definitions, with no rounding:
A microphone sensitivity quoted against 1 µbar reads 20 dB lower than the same figure quoted against 1 Pa, because 1 Pa = 10 µbar.
Watch the case of the letters: mPa is a millipascal and MPa is a megapascal, a factor of a billion apart. For engineering pressures in MPa, psi or bar, use the pressure converter.
Underwater acoustics uses a reference of 1 µPa, not 20 µPa. That alone adds 20 × log₁₀(20) = 26 dB to any figure. Water is also much denser and stiffer than air, so a sound of the same power needs far more pressure. That adds another 35.5 dB.
Together, a sound of equal intensity reads about 61.5 dB higher in water. A level in water cannot be compared with one in air until both steps are made.
Sound intensity follows from pressure: I = p² ÷ (ρ × c). In air with ρc ≈ 415 kg/m²s, 1 Pa carries 0.0024 W/m². Intensity is a flow of power per area, so the heat flux converter uses the same W/m² unit for a different kind of energy flow.
In open space, doubling your distance from a small source drops the level by 6 dB. Two equal, unrelated sources add 3 dB, not double the decibels.
A pressure figure alone cannot tell you whether a noise is safe, because the limits depend on A-weighting and on how long you are exposed. A-weighting reduces low and very high frequencies to match how we hear, so dBA and dB SPL differ.
In the US, OSHA's limit is 90 dBA averaged over an 8-hour day, with a hearing conservation program required from 85 dBA. NIOSH recommends a stricter limit of 85 dBA over 8 hours, and allows half the time for every 3 dB above that. Use a sound level meter set to A-weighting for any exposure question. Frequency also matters, and the frequency converter covers Hz and related units.
The pascal to dyn/cm² relationship is exact. FlowUtil computes with full precision and rounds only the displayed value.
Sound pressure varies with distance, surroundings and frequency weighting, so one decimal place in dB normally matches the measurement.