dBm mW Converter

THE PRACTICAL GUIDE · NORMANDIN SYSTEMS

Get more from dBm mW Converter

dBm mW Converter expresses the same power level measurement in another unit. It is useful when a specification, worksheet, instrument, or reference uses a different scale from the one you need. Power in milliwatts equals 10 raised to the power dBm divided by 10. Therefore 0 dBm equals 1 mW, and 10 dBm equals 10 mW. The numerical value changes because the unit changes; the underlying measured quantity stays the same. dBm is logarithmic power referenced to one milliwatt. A negative dBm value represents positive power below one milliwatt, not negative physical power. Enter the measurement together with its source unit, then read the equivalent in the destination unit. Keep the full result while doing subsequent calculations and round only when preparing the final report. A converted value cannot be more precise than the original measurement, even when the calculator displays many decimal places.

Guide updated October 13, 2026

How to use this tool

1. Enter the numerical power level value. Use the measured value, rather than a rounded intermediate result, to avoid accumulating rounding differences.
2. Use the dBm input or source-unit setting for the worked example. Match the actual unit attached to your source measurement and check any metric prefix carefully.
3. Read the equivalent in mW, or the destination unit required by your calculation. Keep the unit beside the number when copying it.
4. Check the order of magnitude against a familiar conversion. If the result is surprising, recheck the source unit before changing the number.

SEE IT IN PRACTICE

A worked example

0 dBm

1 mW

Power in milliwatts equals 10 raised to the power dBm divided by 10. Therefore 0 dBm equals 1 mW, and 10 dBm equals 10 mW.

Adding power in the correct domain

Two powers expressed in dBm should not be added as ordinary numbers when combining independent power quantities. Convert them to a linear unit such as milliwatts, add the linear amounts when physically appropriate, then convert the total back. A 3 dB increase is approximately a doubling of power, while a 10 dB increase is a tenfold change.

Read a logarithmic power change

An increase from 0 dBm to 10 dBm changes power from 1 mW to 10 mW. A further increase to 20 dBm gives 100 mW. Equal steps in dBm multiply linear power rather than add a fixed number of milliwatts. Negative dBm values are normal below the one-milliwatt reference; for example, −10 dBm corresponds to 0.1 mW.

When this tool is useful

• Prepare consistent power level values for radio link calculations.
• Compare transmitter and receiver power specifications without mentally switching between unit systems.
• Check signal-level unit checks before adding a value to a report or calculation.

Tips for a better result

• dBm is logarithmic power referenced to one milliwatt. A negative dBm value represents positive power below one milliwatt, not negative physical power.
• Use milliwatts as a common reference when comparing values from several sources; keeping one unit throughout a calculation makes dimensional errors easier to notice.
• Retain meaningful significant figures. Extra decimal places are useful for intermediate arithmetic, but do not imply that the original instrument measured with that precision.

Frequently asked questions