Sound Level Unit Converter – dB, Bel and Neper in 3 Easy Steps
Sound Level Converter
Use this sound level unit converter: type a value into any field to instantly convert across all acoustic and logarithmic measurements.
Use this free sound level unit converter to switch between decibels (dB), bels (B), nepers (Np) and millibels (mB). Type a value into any box and the other three update instantly, with a reference chart of the key conversion factors.
Quick answer
1 bel = 10 decibels and 1 decibel = 100 millibels. For field quantities such as sound pressure and voltage, 1 neper = 20 ÷ ln(10) ≈ 8.6859 dB, so 1 dB ≈ 0.1151 Np. That means 85 dB = 8.5 B = 9.786 Np = 8,500 mB.
Table of Contents
Decibels are the everyday unit for loudness, signal strength and gain, but textbooks, telecom specs and older equipment sometimes use bels or nepers. Mixing them up can turn a small difference into a huge one, because these are logarithmic units.
This sound level unit converter handles the conversions exactly, so you can compare figures from any source.
Sound Level Conversion Formulas
- Bels = dB ÷ 10
- Millibels = dB × 100
- Nepers = dB ÷ 8.6859 (field quantities)
- Decibels = Np × 8.6859
- dB from a power ratio = 10 × log₁₀(P₂ ÷ P₁)
- dB from a pressure or voltage ratio = 20 × log₁₀(V₂ ÷ V₁)
Typical Sound Levels
| Sound | Level (dB SPL) | Bels |
|---|---|---|
| Threshold of hearing | 0 dB | 0 B |
| Whisper | 30 dB | 3 B |
| Normal conversation | 60 dB | 6 B |
| Busy traffic | 80–85 dB | 8–8.5 B |
| Lawn mower | 90 dB | 9 B |
| Rock concert | 110 dB | 11 B |
| Threshold of pain | 120–130 dB | 12–13 B |
How to Use the Sound Level Unit Converter
Step 1: Enter a Value in Decibels
Type a level in Decibels (dB). For 85 dB, the converter shows 8.5 B, 9.786 Np and 8,500 mB.
Step 2: Convert Nepers to Decibels
Type in Nepers (Np) to go the other way. 1 Np equals 8.686 dB, 0.869 B and 868.6 mB. Nepers appear in physics, transmission line and filter calculations that use natural logarithms.
Step 3: Check the Reference Matrix
The Base Conversion Reference Matrix shows the main factors: 1 B = 10 dB, 1 dB = 100 mB, 1 Np = 8.6859 dB and 1 dB = 0.1151 Np. Press Clear Fields to start again.
How Decibels Work
- +3 dB doubles the sound power.
- +6 dB doubles the sound pressure (or voltage).
- +10 dB is ten times the power and sounds roughly twice as loud.
- Adding two equal sources raises the level by about 3 dB, not double the number. Two 80 dB machines make about 83 dB.
Where Each Unit Is Used
- Decibels: noise levels, audio gain, speaker sensitivity, Wi-Fi and mobile signal strength.
- Bels: mostly in older texts and as the base unit behind the decibel, named after Alexander Graham Bell.
- Nepers: physics, control systems and telecom attenuation, where natural logarithms make the maths simpler.
- Millibels: some audio software and game engines store volume in millibels to avoid decimals.
Because all four are just different scales of the same logarithm, the sound level unit converter can move between them without knowing what you are measuring.
Hearing Safety
Many workplace rules use 85 dB averaged over 8 hours as an action level for hearing protection. Every 3 dB above that halves the safe exposure time under the common 3 dB exchange rate: about 4 hours at 88 dB and 1 hour at 94 dB. Use hearing protection around loud tools, engines and concerts.
dB, dBA and dB SPL
dB on its own is a ratio. dB SPL is sound pressure relative to 20 micropascals, the threshold of hearing. dBA applies an A-weighting filter that matches how human ears hear different frequencies. Sound level meters usually show dBA. The unit conversion here applies to all of them, because bels and nepers scale the same way.
More unit tools: the Frequency Converter, the Illuminance Converter and the Wavelength to Frequency Calculator.
Frequently Asked Questions
How many decibels are in a bel?
One bel equals 10 decibels.
How do I convert dB to nepers?
Divide decibels by 8.6859. 85 dB ÷ 8.6859 = 9.786 Np.
What is a millibel?
A millibel is one thousandth of a bel, or one hundredth of a decibel.
Does 10 dB louder mean twice as loud?
A 10 dB increase is ten times the sound power and is heard as roughly twice as loud.
Why is 1 neper 8.686 dB?
For field quantities, 1 Np = 20 ÷ ln(10) dB, which is about 8.6859 dB.
Is my data stored?
No. The sound level unit converter runs in your browser and nothing is saved.