mW to dBm converter
Why a logarithmic scale
Because in a link budget everything multiplies: antenna gain, cable loss, path loss. In decibels multiplication becomes addition, and the whole calculation is done in a column. The reference point of the dBm scale is 1 mW.
| mW β dBm | |
| dBm β mW | |
| Reference levels | |
| 0 dBm = 1 mW | the reference level of the scale |
| 14 dBm = 25 mW | the LPD/PMR limit |
| 20 dBm = 100 mW | the Wi-Fi 2.4 GHz limit (EIRP) |
| 30 dBm = 1 W | a handheld on low power |
| 37 dBm = 5 W | a typical handheld transceiver |
| 47 dBm = 50 W | a mobile station |
| 50 dBm = 100 W | a typical HF transceiver |
π The formulasβ
Power in decibels relative to a milliwatt:
P [dBm] = 10 Γ lg(P [mW])
The reverse:
P [mW] = 10^(P [dBm] / 10)
Quick reference:β
| Change | Power ratio |
|---|---|
| +3 dB | Γ2 |
| +6 dB | Γ4 |
| +10 dB | Γ10 |
| +20 dB | Γ100 |
| β3 dB | Γ·2 |
Where this calculator stops:
- dBm is an absolute power, dB a ratio. You may add dB to dBm, but not dBm to dBm
- The logarithm is undefined for zero and negative power
- dBi (antenna gain) and dBm are different quantities: the first is added to the second, it does not replace it
π― In practiceβ
- A link budget: everything in dB, added up in a single column.
- Checking EIRP against the permitted limits.
- Reading datasheets: receiver sensitivity is always given in dBm (β89, β96 and so on).
Practical advice:
- 30 dBm = 1 W is the handiest anchor for mental arithmetic.
- Every +6 dB of EIRP roughly doubles the range in free space.
- Antenna gain buys more than transmitter power: it works on receive as well as transmit.
Β© 2026 UR3PKI Β· CyberDev.Space Β· Content licensed under CC BY-NC-SA 4.0.
How to cite this calculator
UR3PKI. Β«mW to dBm Converter (and dBm to mW)Β». CyberDev.Space. https://cyberdev.space/en/radio/calculators/others/dbm/ (licence CC BY-NC-SA 4.0).The licence lets you use this material freely, including in teaching materials, but only with attribution to the author and a link to the source.