mW to dBm Calculator

Use this tool to convert from milliWatt to dBm.

You can select either Watt, Milliwatt, Microwatt, Nanowatt or Picowatt.

???? dBm to milliWatt

Formula

P_dBm = 10*Log₁₀(P_mW)

What is dBm?

dBm is a unit of power expressed in deciBels referenced to one milliwatt [1]. It is commonly used in Radio frequency, Microwave and Optical communication systems as a measure of absolute power. dBm makes it easy to represent both very large and very small values with few digits.

For example 10,000,000,000,000 mW = 10¹³ mW = 130 dBm

As well, it makes RF budget calculations simpler than with linear values.

What is a Milliwatt?

Milliwatt is a unit of power. It is equivalent to 1/1000 of a Watt. Or 1 mW = 0.001 Watt.

Note the small m to denote milli and not to be confused by capital M which denotes Mega or 10⁶.

How to convert from Milliwatt to dBm

The calculation: 10*Log₁₀(1)= 0 dBm.

1 milliWatt is therefore equal to 0 dBm. 

1000 milliwatt is equal to 30 dBm.

These two numbers are often used by RF engineers and a baseline from which other calculations can be performed.

Let’s take a look at an example below.

What is the dBm equivalent of 2 milliWatt? The same calculation can be performed to give 10*Log₁₀(2) = 10*0.301 = 3 dBm.

Alternatively, we can see that 2 milliWatt is equivalent to two times 1 milliWatt or it represents a ratio of 2:1. This is linear ratio is equivalent to 3 dB. Therefore we can add 3 dB + 0 dBm to give 3 dBm.

With practice is becomes easier to identify these relationships for quick mental conversions but until then you can use the calculator on this page.

Why convert from milliwatt to dBm?

Many times a manufacturer will specify their product in terms of Watt. The power amplifier below is one such example.

However RF engineers will convert this to dBm. Here are a couple of reasons why:

dBm makes it easy to express large numbers. Numbers with many zeros as shown below can be expressed with a smaller number of dBm. For example:

• 0.0000000001 milliWatt = -100 dBm
• 1.0000E-17 mW = -170 dBm
• 10000 mW = 100 dBm

The Logarithmic scale makes this possible.

dBm is convenient to work with. Most RF calculations such as Antenna Range, Wi-Fi RSSI and more are performed using dBm power levels. dBm is also used in conjunction with dB to compute input and output power levels. This involves simple addition or subtraction operations.

mW to dBm Table

Below is a chart of milliWatt to dBm values ranging from 1 mW to 1000 mW.