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

Project details (optional)Add details

Project / jobLocationPrepared byField notes

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: 8/22/2026
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.