What is a dBm to watts conversion calculator?
In RF, audio and instrumentation systems, power levels are often expressed in dBm, a logarithmic unit referenced to 1 milliwatt. While dBm is convenient for dealing with very large dynamic ranges, many design decisions still require linear units such as watts or milliwatts.
This calculator converts instantly between:
- dBm (decibel-milliwatts)
- Watts (W)
- Millliwatts (mW)
Enter either a dBm value or a power level in watts and the tool will compute the corresponding value in the other domain. It is ideal for RF front-ends, wireless links, test setups and audio power calculations.
dBm and watts – the basic relationship
dBm is defined as decibels relative to 1 milliwatt (0 dBm = 1 mW). The conversion formulas are:
-
From dBm to watts:
P(W) = 10((PdBm − 30) / 10) -
From watts to dBm:
PdBm = 10 × log10(P(W) × 1000)
Because dBm is logarithmic, equal steps in dBm correspond to multiplicative factors in power:
- +3 dB ≈ ×2 power
- +10 dB = ×10 power
- −3 dB ≈ ÷2 power
Quick reference table
The table below shows some common dBm levels and their equivalent power in milliwatts and watts:
| dBm | Power (mW) | Power (W) | Typical example |
|---|---|---|---|
| -30 dBm | 0.001 mW | 1 × 10-6 W | Very weak RF signal at receiver input |
| -10 dBm | 0.1 mW | 1 × 10-4 W | Low-level test signal |
| 0 dBm | 1 mW | 0.001 W | Standard dBm reference level |
| 10 dBm | 10 mW | 0.01 W | Small RF transmitter or pre-driver |
| 20 dBm | 100 mW | 0.1 W | Short-range wireless modules |
| 30 dBm | 1000 mW | 1 W | High-power Wi-Fi / ISM band radio |
How to use this dBm to watts calculator
- Choose the input quantity: Decide whether you are starting from a known dBm level or from a power value in watts.
- Enter the value: Type the dBm or watt value into the corresponding field. The calculator will automatically compute the other representation.
- Review the output: In addition to watts, it is often helpful to see the result in milliwatts for low-power RF and in dBW (decibels relative to 1 W) for high-power systems.
- Use the result for link budgets or sizing: Apply the converted value when selecting amplifiers, attenuators, antennas, or checking that your power levels stay within regulatory and device limits.
Design tips for working with dBm and watts
- Keep track of reference points: dBm is always referenced to 1 mW. dBW is referenced to 1 W. Confusing them leads to errors of 30 dB (a factor of 1000 in power).
- Remember cumulative gains and losses: In a signal chain, amplifier gain and cable/connector loss add in dB, but the resulting output power is still best checked in watts or milliwatts.
- Beware of peak vs average power: Modulated signals (OFDM, pulsed radar, etc.) can have large differences between peak and average power. Regulatory limits usually apply to average power.
- Match power levels to device ratings: Ensure that mixers, LNAs, filters and ADCs operate within their specified input power range to avoid distortion or damage.
Using this calculator removes the mental overhead of manual log conversions, so you can focus on designing robust RF links, test setups and mixed-signal systems with the correct power levels at every stage.
