Power measurements are usually made with a user-specified bandwidth. This tool converts this power reading to a normalized value of 1 Hz bandwidth.

dBm per Hz (dBm/Hz) also called Power Spectral Density, is the amount of power in dBm per Hertz of bandwidth.

To convert dBm to dBm/Hz, enter the value and the bandwidth in the calculator below.

## Formula

**P _{dBm/Hz }= P_{dBm} – 10*Log_{10}(B) **

where, **P _{dBm}** is the power measured in Bandwidth

**B**

## Applications of this calculator

**Compare Spectrum Analyzer Noise Floor**

Many spectrum analyzer manufacturers use different bandwidth settings to specify their noise floor.

TinySA’s noise floor specifications state the lowest discernible signal using a resolution bandwidth of 30 kHz of -102 dBm. The calculator can be used to convert this to **-147 dBm/Hz**.

This can be compared with the noise floor of a Siglent Spectrum Analyzer which is more sensitive at **-161 dBm/Hz**. That’s a difference of 17 dB and this makes a benchtop analyzer about 50 times more sensitive than the Tiny SA.

Many times a manufacturer will omit the bandwidth specification when specifying the sensitivity of their instrument. As can be seen in the above examples, the bandwidth influences the number significantly.

**Convert RBW settings**

Let’s say you want to convert a measurement that was made in a 30 kHz resolution bandwidth to 1 MHz resolution bandwidth.

- Use the calculator on this page to normalize from dBm/ 30 kHz to dBm/Hz
- Then enter this number in this calculator along with the desired bandwidth of 1 MHz. This will convert from dBm/Hz to dBm/ 1 MHz

**Notes**

[1] Use this calculator to convert between user-defined values of RBW. For instance to convert from -110 dBm at 10 kHz RBW to 10 MHz RBW.