Watts to dBm Converter
Convert RF power from watts to dBm and dBW. Enter power in watts to get dBm and dBW. Used in RF engineering, cellular and Wi-Fi design.
How to use this tool
- Enter power in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your power and the full breakdown beneath it.
dBm = 10 × log₁₀(P / 1 mW) = 10 × log₁₀(P × 1000), where P is in watts. dBW = 10 × log₁₀(P). Every 10 dBm increase represents a tenfold power increase: 0 dBm (1 mW) → 10 dBm (10 mW) → 20 dBm (100 mW) → 30 dBm (1 W).
Formula
dBm = 10 × log10(P × 1000)
dBW = 10 × log10(P)
where P is power in watts.
How it works
dBm expresses power relative to 1 mW, so the watt value is first multiplied by 1000 to convert to milliwatts before taking the base-10 logarithm and multiplying by 10.
dBW uses the same formula but referenced to 1 W, so the multiplication by 1000 is omitted; as a consequence dBW is always exactly 30 less than dBm for the same power level.
Worked example
Worked example — 1 W
- Input: 1 W.
- Convert to mW: 1 × 1000 = 1000 mW.
- dBm = 10 × log₁₀(1000) = 10 × 3 = 30 dBm.
- dBW = 10 × log₁₀(1) = 10 × 0 = 0 dBW.
30 dBm, 0 dBW, 1000 mW.
Key terms
- dBm
- Decibels relative to one milliwatt; a logarithmic power unit standard in RF and telecommunications.
- dBW
- Decibels relative to one watt; equals dBm minus 30.
- Base-10 logarithm
- log₁₀(x) is the exponent to which 10 must be raised to equal x; log₁₀(1000) = 3.
- Power ratio
- The comparison of one power level to a reference, expressed in decibels as 10 × log₁₀(P/P_ref).
- Milliwatt (mW)
- One thousandth of a watt; the reference power for the dBm scale.
Frequently asked questions
- How much power does a phone transmit?
- A typical smartphone transmits at 0–23 dBm (1 mW to 200 mW) depending on the distance to the cell tower and the band used.
- Why use dBm instead of watts?
- dBm compresses a huge range (picowatts to kilowatts) into a manageable scale and makes gain/loss calculations simple additions and subtractions.