The **Received Signal Strength Indicator** (RSSI) is a measure of the power in a received radio signal. It is commonly used in wireless communication systems to evaluate the signal strength of a received signal.

RSSI is usually measured in dBm (decibels relative to one milliwatt).

**RSSI Formula**

The formula for calculating RSSI typically depends on the specific wireless technology and the implementation by the hardware manufacturer. However, a general approach to calculating RSSI from the received power level can be summarized as follows:

**RSSI = 10*log _{10}(P_{mW})**

where

**P**is the power expressed in milliwatt._{mW}**RSSI**is the power expressed in dBm

Here is a simple calculator that converts received signal power in Watt to RSSI

**What is dBm?**

dBm is a unit of power expressed in deciBels referenced to one milliwatt.

It is commonly used in Radio frequency, Microwave and Optical communication systems as a measure of absolute power. It is used due to the ease of representing both very large and very small values with few digits.

For example 10,000,000,000,000 mW = 10^{13} mW = 130 dBm

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

**Notes**

- As mentioned above the formula for calculating RSSI is manufacturer specific. Here is a calculator to convert from RSSI to dBm.
- RSSI vs dBm – which is a better measure for signal strength?
- How does RSSI vary with distance?