mW ↔ dBm Converter
Use this calculator to convert radio-frequency power between milliwatts (mW) and decibel-milliwatts (dBm). Enter either value and convert in one click.
Formulas: dBm = 10 × log10(mW) and mW = 10^(dBm/10)
What is mW and what is dBm?
Milliwatts (mW) and dBm are two ways to represent power. A milliwatt is a direct linear unit of power, while dBm is a logarithmic unit referenced to 1 milliwatt. Both are commonly used in wireless networking, RF engineering, telecom, and antenna system design.
Linear vs logarithmic scale
- mW (linear): Easy to understand as raw power output.
- dBm (logarithmic): Easier for comparing gains/losses in amplifiers, cables, and antennas.
- Reference point: 0 dBm is exactly 1 mW.
Because dBm is logarithmic, equal dB steps represent multiplication in power. For example, +10 dB means 10× power, and +3 dB is roughly 2× power.
mW to dBm formula
To convert milliwatts to dBm:
dBm = 10 × log10(mW)
Example: Convert 100 mW to dBm
- log10(100) = 2
- dBm = 10 × 2 = 20 dBm
So, 100 mW = 20 dBm.
dBm to mW formula
To convert dBm to milliwatts:
mW = 10^(dBm/10)
Example: Convert 17 dBm to mW
- dBm/10 = 1.7
- mW = 10^1.7 ≈ 50.12 mW
So, 17 dBm ≈ 50.12 mW.
Quick reference chart
| dBm | mW | Common context |
|---|---|---|
| -30 dBm | 0.001 mW | Very weak received signal |
| -20 dBm | 0.01 mW | Low-level RF measurement |
| -10 dBm | 0.1 mW | Low-power test signal |
| 0 dBm | 1 mW | Reference level |
| 10 dBm | 10 mW | Small wireless transmitter |
| 20 dBm | 100 mW | Typical Wi-Fi radio output range |
| 30 dBm | 1000 mW (1 W) | Higher power RF stage |
How to use this mw dBm calculator
- Enter power in mW and click Convert mW → dBm, or
- Enter power in dBm and click Convert dBm → mW.
- Use Clear to reset both fields.
The result panel will show the final conversion clearly with rounded values for practical use.
Where these conversions are used
Wi-Fi and network planning
Router and access point power specs are often discussed in dBm. Understanding mW conversion helps compare devices and estimate coverage while staying within regulatory limits.
Antenna and link budget calculations
When building a link budget, gains and losses are added in dB/dBm. This is much easier than multiplying and dividing linear power values each step.
RF lab testing and troubleshooting
Spectrum analyzers, signal generators, and power meters frequently report values in dBm. Engineers convert to mW when they need absolute linear power for component ratings or thermal checks.
Common mistakes to avoid
- Trying to convert 0 mW to dBm (logarithm undefined).
- Mixing up dB and dBm (dB is relative, dBm is absolute to 1 mW).
- Assuming +3 dB equals exactly double in every decimal context (it is approximately 2×).
- Ignoring cable/connector losses when comparing transmitter output to received power.
FAQ
Can dBm be negative?
Yes. Negative dBm values are simply powers below 1 mW. For example, -10 dBm = 0.1 mW.
Is 30 dBm always 1 watt?
Yes. 30 dBm converts to 1000 mW, which is exactly 1 watt.
Do I need impedance to convert between mW and dBm?
No. Impedance matters when converting voltage/current to power, but mW ↔ dBm conversion is power-to-power and does not require impedance.
Bookmark this page whenever you need fast, accurate power conversion for RF work, wireless setup, or electronics projects.