# dBm to Watts Calculator

URL: https://speedycalculator.com/calculators/conversion/dbm-to-watts/
Last updated: 2026-10-25

> The dBm to watts calculator converts power levels in decibel-milliwatts to watts and milliwatts and back, for radio transmitters, Wi-Fi, fibre optics and RF links.

## Inputs

- Power level (dBm)

## Results

- Power
- In watts
- In dBW

## Formula

```
P (W) = 10^((dBm − 30) ÷ 10)
dBm = 10 × log10(P in mW)
```

## Explanation

dBm expresses power relative to one milliwatt on a logarithmic scale: 0 dBm is 1 mW, 30 dBm is 1 W, and every 3 dB roughly doubles the power. Wi-Fi routers transmit around 20 dBm (100 mW).

### How to use the dBm to Watts Calculator

- **Power level**
- Every result field is editable: type into **Power** or any other result and **Power level** plus every other field update to match.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

The dBm value is divided by 10 and used as a power of ten (in milliwatts). Type watts into the result to get dBm.

### dBm to power table

dBmPower-901 × 10-9 mW-601 × 10-6 mW-300.001 mW-100.1 mW01 mW31.9952623 mW1010 mW20100 mW23199.52623 mW27501.18723 mW301 W331.9952623 W375.0118723 W4010 W50100 W601,000 W

### What each result means

- **Power** = 10 ^ (([Power level] - 30) ÷ 10)
- **In watts** = 10 ^ (([Power level] - 30) ÷ 10)
- **In dBW** = [Power level] - 30

## Worked example

Inputs — Power level: 20 dBm.

Results — **Power = 100 mW**; In watts = 0.1 W; In dBW = -10 dBW.

## FAQ

**How many watts is 30 dBm?**
1 W.

**How many mW is 0 dBm?**
1 mW.

**What does −30 dBm mean?**
0.001 mW, one microwatt.

**What formula does the dBm to Watts Calculator use?**
P (W) = 10^((dBm − 30) ÷ 10).


## Sources

- [NIST Special Publication 811 – Guide for the Use of the International System of Units](https://www.nist.gov/pml/special-publication-811)
- [NIST Handbook 44 Appendix C – General tables of units of measurement](https://www.nist.gov/pml/owm/nist-handbook-44-current-edition)