About the dBm Converter
Decibel-milliwatts, written dBm, express a power level on a logarithmic scale where 0 dBm is exactly one milliwatt. Radio, Wi-Fi, fibre and audio engineers use it because very large and very small powers become easy-to-handle numbers. This dBm converter turns a value in dBm, dBW, milliwatts or watts into all four at once, and also calculates the voltage across a resistive load at the impedance you choose, as RMS and peak-to-peak, along with the current. A pocket-sized reference for working with transmitters, receivers, antennas and signal generators.
Updated October 2026
How to use the dBm Converter
- 1Choose the unit you are converting from: dBm, dBW, milliwatts or watts.
- 2Type the value. dBm and dBW can be negative.
- 3Enter the load impedance, 50 ohms by default.
- 4Read the power in all four units.
- 5Check the RMS voltage, peak-to-peak voltage and current for that load.
Handy values to remember
- 0 dBm = 1 mW
- 10 dBm = 10 mW; 20 dBm = 100 mW; 30 dBm = 1 W
- -10 dBm = 0.1 mW; -30 dBm = 1 microwatt
- +3 dB roughly doubles power; -3 dB roughly halves it
- 0 dBW = 30 dBm; 40 dBm = 10 W
Adding gains and losses
Because decibels are logarithmic, you can add and subtract them. A transmitter at 20 dBm feeding a cable that loses 3 dB and an antenna with 6 dB of gain delivers an effective level of 20 minus 3 plus 6, which is 23 dBm. Convert that to milliwatts to see it is about 200 mW. This is the reason link budgets are written in decibels.
Related electrical tools
For other electrical sums use the Ohm's Law Calculator, the Watts, Amps and Volts Calculator, the Power Converter for horsepower and kilowatts, and the Electrical Unit Converter. When measuring real equipment, remember that voltage readings depend on the true impedance of the circuit and on whether you read RMS, peak or peak-to-peak.
Features
- dBm, dBW, mW and W converted together
- RMS and peak-to-peak voltage across a load
- Current in milliamps
- Any impedance, 50 and 75 ohms common
- Negative dB values supported
- Range checks for impossible inputs
- Runs in your browser
Frequently asked questions
How do I convert dBm to milliwatts?
Raise 10 to the power of (dBm divided by 10). So 0 dBm is 1 mW, 10 dBm is 10 mW, 20 dBm is 100 mW and 30 dBm is 1,000 mW, or 1 watt. Each 3 dB increase roughly doubles the power, and each 10 dB increase multiplies it by ten.
How do I convert milliwatts to dBm?
Take the base-10 logarithm of the power in milliwatts and multiply by 10. For 50 mW, log10(50) is about 1.699, so the result is about 16.99 dBm. The calculator does this when you choose milliwatts as the input.
What is the difference between dBm and dBW?
Both are decibel scales for power. dBm is relative to one milliwatt and dBW is relative to one watt. Because one watt is 1,000 milliwatts, a level in dBm is always 30 more than the same level in dBW. 0 dBW equals 30 dBm.
How do I find the voltage from dBm?
Convert to watts, multiply by the load impedance and take the square root to get the RMS voltage. At 0 dBm into 50 ohms, the power is 0.001 W, giving the square root of 0.05, about 0.2236 volts RMS. Peak-to-peak for a sine wave is about 2.83 times the RMS.
Why is dBm used for Wi-Fi and radio signals?
Received signals can be as weak as a billionth of a milliwatt, and transmitters can be many watts. On the dBm scale that range is something like minus 90 to plus 30, which is easier to read. Gains and losses in cables and amplifiers can be added and subtracted as dB.
What does a negative dBm mean?
It means the power is below one milliwatt. For example minus 30 dBm is 0.001 mW, a microwatt. Wi-Fi signal strengths are usually shown as negative dBm values, where minus 50 is strong and minus 80 is weak.