Decibel Calculator & Sound Level Converter
Convert decibel levels to and from the physical quantity behind them — dB SPL ↔ pascals, dB SWL ↔ watts, dBm, dBW, dBV, dBu and dBFS — add levels by energy, apply distance attenuation, and compute IEC 61672-1 A- and C-weighting at any frequency.
Level ↔ physical quantity
What a sound level meter reads. 1 Pa = 94 dB SPL — the level a field calibrator produces.
Both fields update as you type — edit either side. Reference: 20 µPa, multiplier 20·log₁₀ (field quantity).
Result
dB SPL ↔ sound pressure
93.9794 dB SPL
1 Pa (reference 20 µPa, 20·log₁₀)
Common sound levels and their sound pressure
| Source | dB SPL | Sound pressure | Note |
|---|---|---|---|
| Threshold of hearing (1 kHz) | 0.0 | 2e-5 Pa | The 20 µPa reference itself |
| Rustling leaves / recording studio floor | 20.0 | 0.0002 Pa | Near the limit of most meters |
| Whisper at 1 m | 30.0 | 0.000632 Pa | Quiet bedroom at night |
| Quiet library / suburban night | 40.0 | 0.002 Pa | WHO night-noise guideline outside a bedroom |
| Normal conversation at 1 m | 60.0 | 0.02 Pa | Speech interference starts above this |
| Vacuum cleaner at 1 m | 70.0 | 0.0632 Pa | Loud but not hazardous |
| City traffic / heavy road | 85.0 | 0.356 Pa | OSHA action level: hearing conservation required at 85 dB(A) TWA |
| Acoustic calibrator (1 Pa) | 94.0 | 1 Pa | Exactly 1 Pa — 94 dB is the field-calibration tone |
| Chainsaw / nightclub at 1 m | 100.0 | 2 Pa | NIOSH limit is 15 minutes per day |
| Rock concert / front row | 110.0 | 6.32 Pa | NIOSH limit under 2 minutes per day |
| Jet take-off at 100 m | 120.0 | 20 Pa | Threshold of discomfort |
| Threshold of pain | 130.0 | 63.2 Pa | Immediate risk of permanent damage |
| Jet engine at 25 m | 140.0 | 200 Pa | Impulse limit for unprotected ears |
How these numbers are calculated
- • A decibel is a ratio, not a unit. Every level here is computed against its own reference: 20 µPa for dB SPL, 1 pW/m² for dB SIL, 1 pW for dB SWL, 1 mW for dBm, 1 W for dBW, 1 V for dBV, 0.7746 V for dBu and full scale for dBFS (ISO 1683).
- • Field quantities (pressure, voltage, amplitude) use 20·log₁₀; power-like quantities (power, intensity) use 10·log₁₀. That is why +6.02 dB doubles amplitude while +3.01 dB doubles power.
- • dB SPL, dB(A) and dBm are not inter-convertible by a scale factor — they describe different quantities against different references. Converting between them requires the physical quantity, which is exactly what the first tab does.
- • Levels add by energy, not arithmetic: 80 dB + 80 dB = 83.01 dB, and a source 10 dB quieter than another adds only 0.41 dB to the total.
- • A- and C-weighting use the IEC 61672-1 pole frequencies (20.598997, 107.65265, 737.86223 and 12194.217 Hz) normalised so both read 0 dB at 1 kHz.
- • Everything runs in your browser via JavaScript — no value you enter is sent anywhere. Check the Network tab: zero requests while you calculate.
About Decibel Calculator & Sound Level Converter
A decibel is never a unit on its own — it is a logarithmic ratio between a measured quantity and an agreed reference, so dB SPL, dBm, dBu and dBFS cannot be converted into one another with a scale factor. This calculator is built the correct way instead: every level is tied to the physical quantity it describes and the reference defined for it in ISO 1683 (20 µPa for sound pressure, 1 pW/m² for intensity, 1 pW for sound power, 1 mW for dBm, 1 W for dBW, 1 V for dBV, 0.7745967 V for dBu, full scale for dBFS). Five calculators sit behind one interface: level ↔ physical quantity, decibel ↔ ratio (including bels and both neper conventions), energy summation of several levels, free-field distance attenuation for point and line sources, and IEC 61672-1 A- and C-frequency weighting at any frequency. Everything recalculates as you type.
Why use a Decibel Calculator & Sound Level Converter?
Most online decibel converters treat dB SPL, dB(A), dB HL and dB SWL as interchangeable scales and multiply by one, which silently produces meaningless results — an 85 dB SPL reading is not 85 dBm and is not 85 dB(A). This tool refuses to do that. It converts through the physical quantity with the correct multiplier (20·log₁₀ for pressure, voltage and amplitude; 10·log₁₀ for power and intensity), so 1 Pa really is 93.98 dB SPL, 0 dBm really is 1 mW, and 0 dBu really is 0.7746 V. It also handles the three calculations acousticians actually need daily and that a plain unit table cannot express at all: adding levels by energy, predicting a level at a new distance, and applying the standardised A and C weighting curves.
Who is it for?
Acoustic consultants preparing noise assessments, audio engineers translating between +4 dBu professional line level, −10 dBV consumer level and dBFS in the DAW, RF and broadcast engineers moving between dBm and dBW, machinery vendors converting a datasheet sound power level (dB SWL) into an expected sound pressure level at the operator position, occupational-health officers checking readings against 85 dB(A) action levels, hearing-conservation trainers explaining why 6 dB doubles the amplitude, and students who need the exact formulas rather than a black box.
How to use the tool
Pick a calculator from the tab row: Level ↔ quantity, dB ↔ ratio, Add levels, Distance, or A / C weighting.
In Level ↔ quantity, choose the decibel scale you are working in (dB SPL, dB SIL, dB SWL, dBm, dBW, dBV, dBu or dBFS) — the reference and multiplier for that scale are shown underneath.
Type into either the level field or the physical-quantity field; the other side updates instantly, so 1 Pa reads 93.98 dB SPL and 94 dB SPL reads back as 1 Pa.
Switch the unit selector to read the same quantity in pascals, micropascals, watts, milliwatts, volts or percent of full scale.
Use dB ↔ ratio to turn a decibel figure into an amplitude ratio (10^(dB/20)), a power ratio (10^(dB/10)), bels, or nepers in either the field or the power convention.
Use Add levels to combine uncorrelated sources with L = 10·log₁₀(Σ 10^(Lᵢ/10)) — add a row per source and watch 80 dB + 80 dB resolve to 83.01 dB.
Use Distance to project a measured level to another distance: 20·log₁₀(d₂/d₁) for a point source, 10·log₁₀(d₂/d₁) for a line source, with the full doubling ladder listed beside it.
Use A / C weighting to read the IEC 61672-1 offset at a single frequency and apply it to a level — −19.1 dB at 100 Hz, −26.2 dB at 63 Hz, 0 dB at 1 kHz — then copy any result with the Copy button.
Frequently Asked Questions
How do I convert dB SPL to pascals?
Sound pressure level is defined against the 20 µPa reference from ISO 1683, and pressure is a field quantity, so the multiplier is 20: L = 20·log₁₀(p / 20 µPa), and back the other way p = 20 µPa × 10^(L/20). Open the Level ↔ quantity tab, choose dB SPL, and type into either field. Useful anchors: 20 µPa is exactly 0 dB, 1 Pa is 93.98 dB (the level an acoustic calibrator produces, universally rounded to 94 dB), 0.02 Pa is 60 dB, and 20 Pa is 120 dB. The unit selector also reads the same pressure in µPa, mPa or µbar.
What is the difference between dB SPL, dB(A), dBm, dBu and dBFS?
They measure different physical quantities against different references, so no scale factor converts one into another. dB SPL is sound pressure re 20 µPa. dB(A) is a sound pressure level after the A-weighting filter has been applied — a processing step, not a different unit. dBm is electrical power re 1 mW and dBW is power re 1 W (dBW = dBm − 30). dBV is voltage re 1 V and dBu is voltage re 0.7745967 V, so dBu = dBV + 2.2178 dB. dBFS is digital sample amplitude re full scale, which is why every usable dBFS value is negative. Mapping a microphone's dB SPL to a converter's dBFS requires that specific microphone's sensitivity and the gain staging in between — it is a measurement, not a conversion.
How accurate is this decibel calculator, and does my input leave the browser?
The references are the exact values defined by ISO 1683 (20 µPa, 1 pW/m², 1 pW, 1 mW, 1 W, 1 V, √0.6 V) and the weighting filters use the IEC 61672-1:2013 pole frequencies 20.598997, 107.65265, 737.86223 and 12194.217 Hz, normalised so A and C both read 0 dB at 1 kHz. Results are computed in IEEE 754 double precision and displayed to two or four decimals, which is far finer than any Class 1 sound level meter's ±1.1 dB tolerance. Everything runs in your browser via JavaScript — no value you type is transmitted or logged. Open DevTools' Network tab while you calculate: zero HTTP requests.
dBu, dBV or dBFS — which one should I use?
Use dBu for professional analogue interconnect: nominal line level is +4 dBu, which is 1.228 V RMS. Use dBV for consumer gear and for microphone sensitivity specifications: −10 dBV is 0.316 V RMS, and a typical condenser mic is quoted as about −37 dBV/Pa. Use dBFS once the signal is inside a converter or DAW, where 0 dBFS is the hard clipping ceiling. The relationship between dBu and dBV is fixed at 2.2178 dB (20·log₁₀(1 / √0.6)), but the relationship between either of them and dBFS is set by your converter's headroom specification — commonly +18 or +24 dBu at 0 dBFS — so it must be read from the hardware, not calculated.
Why doesn't 80 dB + 80 dB equal 160 dB?
Decibels are logarithmic, so levels combine by energy, not by arithmetic: L = 10·log₁₀(Σ 10^(Lᵢ/10)). Two uncorrelated 80 dB sources double the acoustic energy, and doubling energy is +10·log₁₀(2) = +3.01 dB, so the total is 83.01 dB. Ten equal sources add 10 dB, not 10×. The corollary matters more in practice: a source 10 dB below another contributes just 0.41 dB to the total, so silencing the quieter machine on a site with a 90 dB and an 80 dB source is almost pointless. Coherent, phase-locked signals are the exception — they can add up to +6.02 dB and are outside this formula.
How much quieter is a machine at 10 metres than at 1 metre?
For a point source radiating into a free field, geometric divergence gives L₂ = L₁ − 20·log₁₀(d₂/d₁), so 100 dB at 1 m becomes 80 dB at 10 m — a 20 dB drop, or 6.02 dB for every doubling of distance (the inverse-square law). A line source such as a busy road or a pipe run spreads cylindrically instead and loses only 10·log₁₀(d₂/d₁), which is 3.01 dB per doubling. Both models assume no barriers, no ground effect, no air absorption and no reflections. Indoors, beyond the reverberation radius, the level stops falling with distance and neither model applies.
Can I convert a dB SPL reading into dB(A)?
Not from a single number. A-weighting is a frequency filter, so converting a broadband level requires the spectrum: weight each band with the IEC 61672-1 A curve and then energy-sum the weighted bands. That is why the weighting tab here is explicitly per-frequency. It shows what the filter does at one frequency — 0 dB at 1 kHz, −19.1 dB at 100 Hz, −26.2 dB at 63 Hz, −50.4 dB at 20 Hz, and a slight +1.2 dB lift at 2 kHz. For a pure tone, adding the offset to the unweighted level is exact. For traffic, machinery or music it is not — measure with the meter set to A, or weight the octave bands and sum them in the Add levels tab.
Where did dB HL go, and how do bels and nepers fit in?
dB HL was removed because it cannot be computed: it is referenced to the median hearing threshold of otologically normal listeners, which is a different sound pressure at every audiometric frequency (per ISO 389), so a dB HL ↔ dB SPL conversion needs an audiometer's transducer-specific RETSPL table, not a formula. Bels and nepers are kept and are exact: 1 bel = 10 dB by definition, while 1 neper = 20/ln10 = 8.685889638 dB in the field/amplitude convention and 10/ln10 = 4.342944819 dB in the power convention. Both are exposed because an unqualified neper figure is ambiguous. For the frequency side of acoustics work, see the frequency converter; for raw pressure units, the pressure converter.
Share This Tool
Found this tool helpful? Share it with others who might benefit from it!
💡 Help others discover useful tools! Sharing helps us keep these tools free and accessible to everyone.