Conversion Tools calculator
Decibel Calculator
This decibel calculator converts between linear values and common logarithmic scales used for power, voltage, sound pressure, and signal gain. It is designed for practical audio, instrumentation, communications, and field-measurement work where you need fast checks in dBm, dBW, dBV, dBu, dB SPL, or simple decibel arithmetic.
Updated July 10, 2026
Doubling power adds 3 dB, while doubling voltage adds 6 dB when impedance stays the same
1 W = 30 dBm | 0 dBu = 0.775 V | 94 dB SPL ≈ 1.00 Pa
Switch between power, voltage, SPL, arithmetic, and gain/loss modes below
Example Calculations
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How to Use
How to use the decibel calculator
Choose the mode that matches the quantity you want to convert, enter the value in linear units or decibels, and review the related output. The calculator supports power levels, voltage levels, sound pressure level, logarithmic dB arithmetic, and input-to-output gain or loss comparisons.
Core decibel relationships
| Mode | Formula | Use Case |
|---|---|---|
| Power | dB = 10 × log10(P ÷ Pref) | RF power, transmitter output, instrument readings |
| Voltage | dB = 20 × log10(V ÷ Vref) | Audio line level, sensors, instrumentation loops |
| Sound Pressure | dB SPL = 20 × log10(p ÷ 20 μPa) | Microphones, room checks, acoustic measurements |
| Arithmetic | Add powers in linear form, then convert back to dB | Combining sources or comparing level differences |
Common Applications
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Frequently Asked Questions
What is the difference between dBm, dBW, dBV, dBu, and dB SPL?
Each decibel scale uses a different reference. dBm is referenced to 1 milliwatt, dBW to 1 watt, dBV to 1 volt, dBu to 0.775 volts, and dB SPL to 20 micropascals of sound pressure. The math is similar, but the reference quantity changes what the number means.
Why does doubling power add 3 dB while doubling voltage adds 6 dB?
Power ratios use 10 × log10(), so doubling power gives about +3.01 dB. Voltage ratios use 20 × log10(), so doubling voltage gives about +6.02 dB, assuming the impedance stays the same. That is why power and voltage decibel values should not be mixed without confirming the reference and impedance basis.
What is 94 dB SPL in pascals?
94 dB SPL is approximately 1 pascal. That reference point is common in microphone and sound-level calibration because it lands very close to a clean round-number pressure value.
Can I add decibel values directly with normal arithmetic?
Only for a simple difference or when you are reporting a change between two readings. When you combine independent levels, you must convert the dB values back to linear power or voltage ratios first, add them there, and then convert the combined result back to decibels.
Why does impedance matter in voltage-based decibel calculations?
Voltage and power are related through impedance. Two voltage readings can represent different power levels if the load changes. When you use voltage-based dB values to estimate power, keep the same impedance basis across the comparison.
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