Enter a power value in watts, milliwatts, or dBm to convert instantly; the calculator also solves for voltage or current when two of the three variables are known.
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Milliwatt Formula
The following formulas are used to convert between milliwatts, watts, and dBm:
mW = W \times 1000
dBm = 10 \times \log_{10}(mW)mW = 10^{dBm/10}Variables:
- mW - power in milliwatts
- W - power in watts
- dBm - power in decibels relative to 1 mW (0 dBm = 1 mW by definition)
What is a Milliwatt?
A milliwatt (mW) is one thousandth of a watt (10-3 W), the SI base unit of power. It is the standard working unit for RF signal strength, optical power in fiber systems, and power consumption in low-energy electronics. The symbol mW combines the SI prefix milli (m) with the unit watt (W), named after James Watt (1736-1819).
Real-World Milliwatt Power Levels
The table below lists typical power levels for common devices and signals. These figures span over 10 orders of magnitude, illustrating why the logarithmic dBm scale is preferred in RF and optics work.
| Device / Signal | Typical Power (mW) | dBm |
|---|---|---|
| Cardiac pacemaker (output pulse) | 0.0001 mW | -40 dBm |
| Bluetooth LE (receive threshold) | 0.0001 mW | -40 dBm |
| WiFi receive sensitivity (802.11n) | 0.00001 mW | -50 dBm |
| Hearing aid (microphone input) | 0.001 mW | -30 dBm |
| Bluetooth LE (transmit, typical) | 1 mW | 0 dBm |
| Laser pointer, Class II (FDA max) | 1 mW | 0 dBm |
| Laser pointer, Class IIIa (FDA max) | 5 mW | 7 dBm |
| WiFi router (indoor, 2.4 GHz) | 100 mW | 20 dBm |
| Cell phone transmit (LTE, typical) | 125-250 mW | 21-24 dBm |
| Cell phone transmit (LTE, max) | 2,000 mW | 33 dBm |
| LED indicator light | 10-150 mW | 10-22 dBm |
| Laptop (active use) | 15,000-65,000 mW | 42-48 dBm |
dBm to mW Quick Reference
dBm is the dominant unit in RF engineering because signal levels span many decades of power. Every +10 dBm doubles the power roughly 3 times (10x increase); every +3 dBm approximately doubles power. The table below covers the range used in WiFi, cellular, and fiber optic work.
| dBm | mW | W | Typical Context |
|---|---|---|---|
| -90 dBm | 0.000000001 mW | 0.000000000001 W | WiFi: unusable signal |
| -70 dBm | 0.0000001 mW | 0.0000000001 W | WiFi: fair signal (web browsing) |
| -67 dBm | 0.0000002 mW | 0.0000000002 W | WiFi: minimum for video streaming |
| -50 dBm | 0.00001 mW | 0.00000001 W | WiFi: good signal |
| -30 dBm | 0.001 mW | 0.000001 W | WiFi: excellent / very close to AP |
| 0 dBm | 1 mW | 0.001 W | Reference level; BLE transmit |
| +10 dBm | 10 mW | 0.01 W | Some WiFi adapters |
| +20 dBm | 100 mW | 0.1 W | WiFi router (FCC Part 15 limit) |
| +30 dBm | 1,000 mW | 1 W | Cellular base station antenna port |
| +40 dBm | 10,000 mW | 10 W | Amateur radio HF transceiver |
Conversion Examples
Watts to milliwatts: 0.12 W x 1000 = 120 mW
Milliwatts to watts: 250 mW / 1000 = 0.25 W
Milliwatts to dBm: 100 mW = 10 x log10(100) = 20 dBm
dBm to milliwatts: 17 dBm = 10^(17/10) = 50.1 mW
