Sound Level Converter
Convert decibels, pascals, sound intensity, nepers, sones and phons — a logarithmic scale with a fixed reference, which is why doubling the sound adds three decibels rather than doubling the number.
Sound Level Converter
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- A-weighting cannot be derived from an unweighted level without the frequency spectrum; exposure figures treat the entered value as already A-weighted.
- Distance behaviour assumes a point source in free field and does not hold indoors past the critical distance.
- Phon and sone crossings to physical levels are refused because they require an ISO 226 equal-loudness contour.
In short: The decibel is not a unit but a logarithmic ratio against a reference. Sound pressure level is 20·log₁₀(p / 20 µPa), so 1 Pa is 93.98 dB SPL and the 94 dB calibrator tone is almost exactly one pascal. Because the scale is logarithmic, two identical sources add 3 dB, not 6, and doubling your distance from a point source subtracts 6 dB.
Formula
There is no factor table on this page because there cannot be one. Every decibel figure is a logarithm of a ratio against a fixed reference, so conversion is exponential in one direction and logarithmic in the other.
Worked Example
- Start from the reference. Sound pressure level references 20 micropascals, fixed by ISO 1683.
- Form the ratio. For 94 dB, p/p₀ = 1094/20 = 50,119.
- Multiply by the reference. 50,119 × 20 µPa = 1.0024 Pa, which is why the 94 dB calibrator tone is treated as one pascal.
- Use 20 for pressure, 10 for power. Intensity and acoustic power use 10·log₁₀ because intensity goes as pressure squared.
- Never add decibels arithmetically. Two 94 dB sources give 97.01 dB, not 188.
Why two lawnmowers are not twice as loud. Run one 90 dB mower and the sound power at your ear is some value. Start a second identical one and you have doubled the acoustic power, which on a logarithmic scale is 10·log₁₀(2) = 3.01 dB. The pair measures 93 dB, not 180 and not 96. Perceptually the increase is barely noticeable, because the ear needs roughly ten times the power — a full 10 dB — before most listeners describe a sound as twice as loud. This is also why removing one noisy machine from a room full of them changes almost nothing.
Strengths & Limits Of This Model
Where this engine is strong
- Treats sound level as the logarithmic quantity it is, with no misleading linear factor table.
- Combines sources logarithmically and shows the 3.01 dB doubling explicitly.
- Gives both the OSHA and NIOSH exposure durations, which differ by a factor of eight at 100 dBA.
Where it stops
- Not a sound level meter or a noise-exposure compliance record.
- Does not perform octave-band or A-weighted spectral analysis.
- Room acoustics, reverberation and absorption are outside its scope.
Practical Use Cases
Occupational noise assessment
Comparing a measured dBA level against OSHA's 90 dBA eight-hour limit on a 5 dB exchange rate or NIOSH's 85 dBA on a 3 dB rate, which give very different allowable durations.
Audio and studio calibration
The 94 dB SPL calibrator tone is one pascal, which is the anchor point for microphone sensitivity figures quoted in mV/Pa.
Environmental and building acoustics
Predicting how a source level falls with distance, and combining multiple sources logarithmically rather than by addition.
Product noise specification
Appliance ratings in sones translate to phons and back — pair with the Frequency Converter when working with octave-band data.
Methodology & Editorial Standards
Sound level is handled as a logarithmic quantity throughout, with no linear factor table, because none exists. Sound pressure level uses L = 20·log₁₀(p/p₀) with p₀ = 20 µPa as specified in ISO 1683:2015 and IEC 61672-1. Intensity level uses L = 10·log₁₀(I/I₀) with I₀ = 10⁻¹² W/m², and sound power level the same form with W₀ = 10⁻¹² W. Underwater acoustics references 1 µPa, producing a fixed offset of 26.02 dB against the airborne scale. Pressure crosses to intensity only through I = p²/ρc using the characteristic impedance you select. The neper relates to the decibel as 1 Np = 8.685889638065035 dB and the bel as 1 B = 10 dB. Loudness uses sone = 2^((phon−40)/10). Crossings to acoustic power, to bare ratios and to the loudness scales are refused, because they require a radiating geometry, a stated reference and an ISO 226 equal-loudness contour respectively. Exposure durations apply the OSHA 90 dBA / 5 dB and NIOSH 85 dBA / 3 dB rules to the entered level treated as A-weighted. All conversion factors are exact by definition under the International System of Units, or exact by international agreement where the unit is defined by treaty. Values are held at full IEEE-754 double precision internally and rounded only for display, so chained conversions do not accumulate drift.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Sound Level Converter — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How many pascals is 94 dB SPL?
1.0024 pascals, which is why 94 dB is the standard acoustic calibrator level: it is as near to exactly one pascal as makes no difference. One pascal itself is 93.979 dB SPL. Microphone sensitivity is quoted in millivolts per pascal for this reason, and a calibrator lets you tie a voltage reading directly to a known pressure.
Why do two identical sounds add only 3 dB?
Because the decibel is logarithmic. Two identical sources double the acoustic power, and 10·log₁₀(2) is 3.0103 dB. Ten identical sources add 10 dB, and a hundred add 20 dB. Arithmetic addition of decibels is always wrong: 90 dB plus 90 dB is 93 dB, not 180. A source 10 dB quieter than another contributes only 0.41 dB to the total.
What is 0 dB SPL?
Not silence, but a sound pressure of exactly 20 micropascals, the reference fixed by ISO 1683 and chosen to approximate the quietest 1 kHz tone a healthy young ear can detect. Sounds quieter than that produce negative decibel levels, which are entirely legitimate: a good anechoic chamber sits around −20 dB SPL.
How much does sound drop off with distance?
For a point source in free field, 6.02 dB per doubling of distance, because pressure falls as one over the radius. Ten times the distance costs 20 dB. This holds only outdoors or in an anechoic space; inside a room, past the critical distance where reflected sound dominates, the level stops falling and flattens out entirely.
What is the difference between dB and dBA?
dB SPL is the unweighted physical sound pressure level. dBA applies the A-weighting filter, which rolls off low frequencies to approximate how the ear responds at moderate levels. There is no conversion between them without knowing the spectrum of the sound: a broadband hiss and a deep rumble at the same dB SPL can differ by tens of dBA. Occupational limits are always stated in dBA.
Why do OSHA and NIOSH give different exposure limits?
They use different exchange rates. OSHA permits 90 dBA for eight hours and halves the allowable time for every 5 dB increase, so 95 dBA gives four hours. NIOSH recommends 85 dBA for eight hours and halves for every 3 dB, so 95 dBA gives just 47 minutes. The gap widens with level: at 100 dBA OSHA allows two hours and NIOSH fifteen minutes, an eightfold difference.
What is a neper?
The natural-logarithm counterpart of the decibel, used mainly in transmission-line and filter theory. One neper is the natural log of an amplitude ratio, and equals 8.685889638 dB. The bel, from which the decibel takes its name, is simply 10 dB and is almost never used directly because it is too coarse a step.
What is the difference between a sone and a decibel?
A decibel measures physics and a sone measures perception. The sone scale is linear in loudness, so 4 sones genuinely sounds twice as loud as 2 sones, whereas doubling perceived loudness takes about 10 decibels and ten times the acoustic power. One sone is defined as 40 phon, which is a 40 dB SPL tone at 1 kHz. Appliance ratings use sones because the numbers behave the way listeners expect.