Watts to dBm Calculator
Convert RF watts, milliwatts, dBW, EIRP, voltage, current, and link-budget power levels for Wi-Fi, SDR, ham, IoT, and home lab radio work.
RF power conversion results
| Watts | Milliwatts | dBm | dBW | Common RF meaning |
|---|---|---|---|---|
| 0.000001 W | 0.001 mW | -30 dBm | -60 dBW | Very small received signal power |
| 0.00001 W | 0.01 mW | -20 dBm | -50 dBW | Strong receiver input in many RF tests |
| 0.0001 W | 0.1 mW | -10 dBm | -40 dBW | Low-level lab signal source |
| 0.001 W | 1 mW | 0 dBm | -30 dBW | The dBm reference point |
| 0.01 W | 10 mW | 10 dBm | -20 dBW | SDR output or tiny transmitter |
| 0.1 W | 100 mW | 20 dBm | -10 dBW | Common Wi-Fi conducted power |
| 1 W | 1000 mW | 30 dBm | 0 dBW | One watt radio reference |
| 10 W | 10000 mW | 40 dBm | 10 dBW | Small RF power amplifier |
| Scenario | Conducted power | Typical gain/loss | Approx EIRP | Planning note |
|---|---|---|---|---|
| Indoor Wi-Fi access point | 100 mW / 20 dBm | +3 dBi, -0.5 dB | 22.5 dBm | Use per-chain settings in controller UI. |
| Outdoor point-to-point bridge | 500 mW / 27 dBm | +13 dBi, -2 dB | 38 dBm | Directional antenna gain dominates EIRP. |
| LoRa sensor node | 25 mW / 14 dBm | +2 dBi, -0.5 dB | 15.5 dBm | Low duty cycle affects average power. |
| SDR bench generator | 10 mW / 10 dBm | 0 dBi, -3 dB pad | 7 dBm | Attenuators protect receiver front ends. |
| BLE or Thread device | 1 mW / 0 dBm | +1 dBi, 0 dB | 1 dBm | Small power changes matter indoors. |
| Ham QRP station | 5 W / 37 dBm | +6 dBi, -1.5 dB | 41.5 dBm | Feedline loss rises with frequency. |
| Power | dBm | Vrms at 50 ohm | Irms at 50 ohm | Why it matters |
|---|---|---|---|---|
| 1 mW | 0 dBm | 0.224 V | 4.47 mA | Reference level for lab RF power. |
| 10 mW | 10 dBm | 0.707 V | 14.14 mA | Small source or attenuated transmitter. |
| 100 mW | 20 dBm | 2.236 V | 44.72 mA | Common AP radio output scale. |
| 1 W | 30 dBm | 7.071 V | 141.4 mA | One watt into a matched RF load. |
| 5 W | 37 dBm | 15.811 V | 316.2 mA | QRP transmitter or small amplifier. |
| 10 W | 40 dBm | 22.361 V | 447.2 mA | Needs rated coax, loads, and cooling. |
| Change | Power ratio | Example from 20 dBm | Field use |
|---|---|---|---|
| +3 dB | About 2x | 23 dBm, about 200 mW | Doubling power or antenna gain step. |
| -3 dB | About 1/2 | 17 dBm, about 50 mW | One splitter, pad, or cable loss chunk. |
| +6 dB | About 4x | 26 dBm, about 400 mW | Large antenna gain improvement. |
| +10 dB | 10x | 30 dBm, 1 W | One decade of RF power. |
| -10 dB | 1/10 | 10 dBm, 10 mW | Attenuator pad or heavy feedline loss. |
| +20 dB | 100x | 40 dBm, 10 W | Amplifier gain or big dish antenna step. |
Formula check: dBm = 10 x log10(watts x 1000). Watts = 10^((dBm - 30) / 10). EIRP dBm = conducted dBm + antenna gain - losses.
Every radios system eventually encounter a translation problem between the unit of power (watts or milliwatts) and the unit of power use in radio systems (dBm). The wattage must to be converted into dBm because the dBm unit are a logarithmic scale. Changes to dBm indicate changes to the raw wattage of the radio system.
For example, a 3 dB increases in power mean that the raw wattage has doubled; a 10 dB increase in power mean that the raw wattage has increased 10 times. A 20 dBm transmitter differ from a 23 dBm transmitter in that the 20 dBm use 100 mW of power compared to 200 mW for the 23 dBm transmitter. When using a power calculator, the user must select the correct power unit for the radio system.
How to Use a Radio Power Calculator
Most radio manufacturer specification will list the conducted power of the radio system, which is the power of the signal measured at the connector of the radio system before it exit into the antenna. However, some specification will list the EIRP of the radio system. EIRP takes into account the gain of the antenna as well as the loss of the cable that connects the radio to the antenna.
Therefore, in this case, the wrong power value will produce incorrect calculation in the power calculator; the power calculator allow for the addition of antenna gain and the subtraction of cable loss to allow for the viewing of the difference between these two power specifications. Impedance is a factor in the calculation of voltage or current from a radio system. Most radio system use an impedance of 50 ohms.
Voltage and current calculation are made based on the assumption of 50 ohms of impedance. In instances in which other impedances are used, such as 75 ohms for video signals or unusual balanced line impedances, the user must change the impedance in the power calculator so that the voltage and current calculation are accurate. Another factor to consider is duty cycle, which is often overlooked when calculating peak power or average power.
Peak power is used to determine if the signal from the radio system being calculated will overload a receiver for another signal. Peak power is also used to determine if an amplifier will remain within its linear region. Average power relate to the amount of heat generated by the radio system and the life of its battery as well as to regulatory requirement for that radio system.
The percentage value of the duty cycle can be enter directly into the power calculator so that both the peak and average power can be displayed. For example, if the radio system is a LoRa node, the node may only need to transmit for a small percentage of time. In this case, high peak power can be used while keeping the average power of the node low.
Conversely, high peak power that a data link uses continuously will quickly exceed the thermal and regulatory power limit for that node. Many real-world installations are not the same than those described in the datasheet for that component. For example, in the real world, radio signal often must pass through connectors, lightning arrestors, and splitters.
Additionally, the power of radio signals often diminish with the length of the cable and the frequency at which it is transmitted. These losses can be entered into the power calculator directly so that the resulting EIRP for the radio system is accurate. Many link problem in the field are created because someone assume that every connector and every length of coaxial cable have no loss of signal power.
When comparing different radio systems, caution must be use because different manufactures use different method of measuring power. For instance, some manufacturers specify power for a MIMO system with four radio system chains as a total power value that include the power of the four radio system chains. If that total value is entered into a calculator for a single radio system chain, the power level of that chain will be overestimated.
The chain selector for the power calculator will automatically divide the total power by the number of chains to provide the correct power level for each chain as measured by the regulatory agency. The planning margin account for power losses due to aging connectors over time or changes in the foliage seasonally, or the number of active device in the same portion of the radio spectrum at the same time. A planning margin of 10 percent of the calculated power is typical when designing a link.
This planning margin is applied to the calculated power for the system. The planning margin may be adjust according to the environment where the radio system is to be deployed. The decision of which power value will be used and which losses will be subtracted from the raw power of the radio system is the most important task in using a power calculator.
