Authoritative definitions of the International System of Units and SI prefixes.
Unit conversion
Watts to Decibel-milliwatts Converter
1 W = 30 dBm. Enter a value to convert W to dBm, then use the formula and table below. Displayed digits may be rounded.
Electrical unitsInstant result
Decimals
Formula result = 10 × log10(input × 1) + 30. 1 W = 30 dBm
Nonzero results too small for the selected decimal places use scientific notation.
Nonzero results too small for the selected decimal places use scientific notation.
Common examples
One value, several units
Kilowatts0.001 kW
Megawatts1.00000e-6 MW
Decibel-milliwatts30 dBm
Conversion table
| W | dBm |
|---|---|
| 1 W | 30 dBm |
| 2 W | 33.0103 dBm |
| 5 W | 36.9897 dBm |
| 10 W | 40 dBm |
| 25 W | 43.9794 dBm |
| 50 W | 46.9897 dBm |
| 100 W | 50 dBm |
Conversion chart
1 W30 dBm
5 W36.9897 dBm
10 W40 dBm
25 W43.9794 dBm
50 W46.9897 dBm
Worked example
1 W = 30 dBm. Apply the selected conversion formula to other input values.
Unit definition
Watts (W) One watts equals 1 watt.
Unit history
The watt is named for James Watt and is the SI unit of power, equal to one joule per second.
Step by step
1. Parse the value, including fractions.
2. Convert W to watt.
3. Convert the base value to dBm and apply your display precision.
Understand the result before using it
Watts to Decibel-milliwatts converts a value measured in Watts (W) into the equivalent value in Decibel-milliwatts (dBm). The numerical value changes because the size and definition of the selected unit changes; the underlying quantity does not.
Calculated result
The conversion follows the displayed unit relationship. Display rounding can hide additional digits, and measured inputs cannot become more accurate merely by changing units.
Formula, assumptions, and example
Formula
result = 10 × log10(input × 1) + 30
Assumptions
- Watts and Decibel-milliwatts represent the same electrical power quantity.
- The input is expressed in W; the output is expressed in dBm.
- The unit definitions and conventional relationship shown on this page apply.
Worked example
1 W = 30 dBm. For another value, apply the same relationship and round only to the precision your source measurement supports.
When to use it
Good uses
- Read a W measurement in a document that expects dBm.
- Compare a watts value with a value reported in decibel-milliwatts.
- Check the W to dBm arithmetic before copying the result into another calculation.
Limitations
Common mistakes to avoid
- Do not confuse W with another unit that has a similar name or symbol.
- Round the output to a precision justified by the original measurement.
- Verify safety-critical, regulated, laboratory, and contractual conversions against the controlling standard.
Sources and further reading
These references explain the underlying standards or provide authoritative context. Your own contract, institution, clinician, product documentation, local code, or governing standard may be the controlling source.
Guidance on unit names, symbols, conversions, and numerical presentation.
Questions about this calculation
How do I convert Watts to Decibel-milliwatts?
result = 10 × log10(input × 1) + 30. Input is in W; result is in dBm. 1 W = 30 dBm. The displayed digits may be rounded.
What is 1 W in dBm?
1 W = 30 dBm. The displayed digits may be rounded. Use the full formula for other inputs; offset, reciprocal, and logarithmic scales cannot generally use this example as a multiplier.
Can I reverse the W to dBm conversion?
Yes. Swap the source and target units in the converter. The reverse relationship converts dBm back to W.
Is the Watts to Decibel-milliwatts result exact?
The conversion follows the displayed unit relationship. Display rounding can hide additional digits, and measured inputs cannot become more accurate merely by changing units.