# Watts to dBm Calculator

Watts to dBm calculator for RF, WiFi, and radio power. Also converts dBm to watts with a dBm to watts table (5 watts to dBm = 36.99, 10 watts to dBm = 40).

## What this calculates

Convert between watts and dBm for radio, WiFi, cellular, and satellite power calculations. Enter watts to get dBm, or switch the direction to convert dBm to watts. The tool also shows milliwatts and dBW for quick cross-reference.

## Inputs

- **Direction** — options: Watts to dBm, dBm to Watts — Choose whether to convert watts to dBm or dBm back to watts.
- **Value** — min 0 — Enter the power value. For watts use the value in W (e.g., 5). For dBm use the value in dBm (e.g., 30).

## Outputs

- **dBm** (dBm) — Power in decibel-milliwatts.
- **Watts** (W) — Power in watts.
- **Milliwatts** (mW) — Power in milliwatts.
- **dBW** (dBW) — Power in decibels relative to 1 watt (dBm minus 30).

## Details

dBm (decibel-milliwatts) is a logarithmic unit of power relative to one milliwatt. It is the standard unit used in RF engineering, wireless networking, and radio broadcasting because it turns wide power ranges into manageable numbers and multiplication into addition.

**Watts to dBm formula:**

dBm = 10 × log10(P × 1000), where P is power in watts.

An equivalent form is dBm = 30 + 10 × log10(W), which is the version most often seen in a **watts to dbm formula excel** sheet: the cell formula is usually "=30+10*LOG10(A1)".

**dBm to watts formula:**

Watts = 10^((dBm − 30) / 10)

## Common watts to dBm reference

| Watts | dBm | Context |
|-------|-----|---------|
| 0.001 W (1 mW) | 0 dBm | Bluetooth Class 3 |
| 0.01 W | 10 dBm | Low-power WiFi |
| 0.1 W | 20 dBm | WiFi client TX (100 mW) |
| 1 W | 30 dBm | Max FCC WiFi EIRP (point-to-multi) |
| **5 W** | **36.9897 dBm** | Ham radio handheld |
| **10 W** | **40 dBm** | Ham radio mobile (low) |
| 25 W | 43.9794 dBm | Public safety radio |
| **50 W** | **46.9897 dBm** | Mobile ham / amateur HF |
| 100 W | 50 dBm | Amateur HF transceiver |
| 1,000 W | 60 dBm | AM radio low-power |

This dBm to watts table uses the exact formula dBm = 30 + 10 × log10(W), rounded to four decimal places. Every 3 dB step is a power doubling, every 10 dB step is a 10× power increase.

## Why engineers use dBm

Adding dB values is easier than multiplying linear power. If an amplifier has 20 dB gain and the input is 10 dBm, the output is 30 dBm. No multiplication required. Path loss, antenna gain, and receiver sensitivity are all expressed in dB or dBm for the same reason.

## Quick mental shortcuts

- +3 dB = double the watts
- +10 dB = 10× the watts
- +20 dB = 100× the watts
- −3 dB = half the watts

## Frequently Asked Questions

**Q: How do I convert watts to dBm?**

A: Use the formula dBm = 10 × log10(W × 1000), or equivalently dBm = 30 + 10 × log10(W). For example, 1 W = 30 dBm, 5 watts to dBm = 36.9897 dBm, 10 watts to dBm = 40 dBm, and 50 watts to dBm = 46.9897 dBm.

**Q: How do I convert dBm back to watts?**

A: Use the inverse formula: Watts = 10^((dBm − 30) / 10). A handy dBm to watts table: 0 dBm = 0.001 W, 10 dBm = 0.01 W, 20 dBm = 0.1 W, 30 dBm = 1 W, 40 dBm = 10 W, 50 dBm = 100 W. Each 10 dBm step is a 10× change in watts.

**Q: What is the watts to dBm formula in Excel?**

A: In Excel or Google Sheets, put your watt value in cell A1 and use '=30+10*LOG10(A1)' to get dBm. For the reverse, use '=10^((A1-30)/10)' where A1 holds a dBm value. These formulas give the same results as this calculator.

**Q: Why is 5 watts to dBm equal to 36.99 and not exactly 37?**

A: Because 5 is not a round power of 10. The exact result is 30 + 10 × log10(5) = 30 + 6.9897 = 36.9897 dBm. Rounding to one decimal gives 37.0 dBm, which is why many spec sheets list a 5 W transmitter as '~37 dBm' even though the precise value is 36.99 dBm.

**Q: Is dBm the same as dBW?**

A: No. dBm is referenced to 1 milliwatt, dBW is referenced to 1 watt. They differ by exactly 30 dB: dBW = dBm − 30. So 40 dBm = 10 dBW = 10 W. The calculator outputs both so you can switch between references without a second conversion.

**Q: What dBm level is considered safe for WiFi equipment?**

A: In the US, the FCC limits WiFi transmitters to 30 dBm (1 W) conducted power in the 2.4 GHz band, with EIRP limits depending on antenna gain and deployment type. Typical consumer access points transmit at 17 to 23 dBm (50 to 200 mW). Higher power is only allowed for point-to-point links.

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Source: https://vastcalc.com/calculators/conversion/watts-dbm
Category: Conversion
Last updated: 2026-04-08