What is 0 dBm in milliwatts?

0 dBm equals exactly 1 milliwatt because dBm is referenced to 1 mW.

How do I convert dBm to mW?

Use P(mW) = 10 raised to P(dBm) divided by 10.

How do I convert mW to dBm?

Use P(dBm) = 10 times log base 10 of P(mW). Milliwatts must be greater than zero.

Is dBm the same as dB?

No. dBm is an absolute power level referenced to 1 mW. dB expresses a ratio or gain/loss and has no absolute power reference by itself.

dBm to mW Converter — Optical Power Calculator

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How to use this calculator

Choose whether your source value is dBm or milliwatts.
Enter the optical power exactly as shown by the data sheet or instrument.
Choose display precision; calculations always retain full precision.
Review all equivalent power units, then export or share if needed.

Step 1 · Direction

What unit do you have?

Optical Power Conversion Report

CALCULATED

Report date: 10/18/2026
Direction: dBm to mW

Engineering use

Unit conversion based on the entered optical power. Confirm the source value, unit, sign, instrument calibration, and equipment data sheet before design acceptance.

Primary conversion

-10 dBm = 0.1 mW

The conversion uses the exact entered value and full-precision logarithmic math. The selected significant digits affect presentation only.

dBm-10

Milliwatts0.1 mW

Watts0.0001 W

Microwatts100 µW

Interpretation

What the result means

dBm is an absolute logarithmic power level referenced to 1 milliwatt. Every increase of 10 dB multiplies linear power by 10; every decrease of 10 dB divides it by 10.

Do not substitute dB for dBm. dB is a ratio and requires a reference power before it represents an absolute level.

Calculation method

Formulas and verification

dBm to mW: P(mW) = 10^(P(dBm) / 10)
mW to dBm: P(dBm) = 10 × log10(P(mW))
Reference point: 0 dBm = 1 mW

Verification: Preserve signs and confirm whether the source expresses absolute power in dBm or a gain/loss ratio in dB.