dBm to mW Calculator

Use this calculator to convert dBm to mW or milliWatt.

? mW to dBm

Formula

P_mW = 10^{(P_dBm / 10)}

Background

dBm stands for deciBel referenced to one milliwatt. It is commonly used by RF engineers in the context of absolute power levels associated with various components such as filters, mixers, amplifiers, splitters, combiners and more.

People often confuse dBm with dB. dB or deciBel has no units and represents the logarithm of a power or amplitude ratio.

Watt is a unit of power or radiant flux. It is equivalent to 1 joule per second or 1 kg⋅m²⋅s⁻³. Milliwatt is one Watt divided by one thousand or 0.001 W.

Note: Watt is a unit of power in the International System of Units (SI). dBm however is not in the International System of Units.

Where is milliwatt used?

milliwatt is used in electrical engineering power calculations. Its use is more widespread than dBm. milliwatt is used in radio frequency and wireless, power systems and more.

You won’t encounter milliwatt in commercial audio systems as speaker or amplifier wattage is usually specified in Watt.

Where is dBm used?

dBm is used in link budgets, antenna range computation, noise floor calculations and more. It’s easy to work with both dBm and dB as they require simple addition and subtraction. By comparison, working with Watt involves a larger range of number values that have to be multiplied and divided.

We also use dBm with our communication technologies. For instance, Wi-Fi signal strength – also known as RSSI (Received Signal Strength Indicator) is measured in terms of dBm. The higher the dBm value, the better the signal. The dBm value relates directly to Internet speed.

dBm values for signal strength in 4G, 5G and Wi-Fi measured on a phone or tablet are almost always negative. It might be confusing at first, but the more negative the value, the worse the signal. For instance, -85 dBm represents a weaker signal relative to -45 dBm.

Why convert from dBm to milliwatt?

The maximum input to an RF module can sometimes be specified in milliWatt. If the output from a circuit that feeds the module is specified in dBm, then it would make sense to convert this value to milliWatt to check if it’s under the limit.

Another instance is when calculating the Power Added Efficiency. Defined as the ratio of the difference between the output and input power to the DC power consumed. In this case, the entire calculation is performed in Watt with the formula below:

PAE = 100*(P_RFOUT – P_RFIN)/P_DC

In this case each of these quantities if specified in dBm, should be converted to Watt before using the formula.

dBm to MilliWatt Table