Decibel Converter: dB, dBm, dBV & Examples

Input Parameters

Conversion Type

Unit

Reference Level

Formulas

dB=10\log_{10}\left(\dfrac{P}{P_{ref}}\right)

P=P_{ref}\cdot10^{\dfrac{dB}{10}}

Gain=\dfrac{P}{P_{ref}}

Results & Set Parameters

Decibels

dBm

Reference Level

Value

Gain

Measurement guide

Use decibels without ambiguity

A decibel expresses a logarithmic ratio. It becomes an absolute quantity only when a reference, such as 1 mW for dBm or 1 V for dBV, is explicitly stated.

Method and assumptions

For power, the ratio is 10·log10(P2/P1). For voltage or current measured with the same impedance, it is 20·log10(X2/X1). The calculator keeps references separate so gain, loss, and absolute level are not confused.

Inputs to verify

Quantity type

Select power, voltage, current, or sound pressure before converting.

Reference and impedance

dBm, dBV, and dBu do not share the same reference. A voltage-to-power conversion also needs the system impedance.

Recommended workflow

1Identify whether you have a ratio or a referenced level.
2For voltage, record the impedance at which the measurement is defined.
3Keep the sign: a passive loss is expressed as negative gain.

Checkable example

10 mW relative to 1 mW is 10 dBm. Doubling power adds about 3 dB; doubling voltage at the same impedance adds about 6 dB.

Limits to keep in mind

dB values do not replace a calibrated measurement chain. Variable impedances, peak quantities, and wideband signals require an explicit convention.

Frequently asked questions

Are dBm and dB interchangeable?

No. dBm is a power level referenced to 1 mW; dB is only a ratio.

Why use 20·log for voltage?

At constant impedance, power is proportional to voltage squared. The factor of 20 accounts for that square.

References to consult

Method references: dB/dBm/dBV/dBu conventions and the reference impedance documented by the measurement equipment.

Original educational content, reviewed for technical clarity on 20 August 2026. Always verify datasheets, applicable standards, and your design before power-up or manufacture.