What is the formula to convert watts to dBm?

dBm = 10 × log10(P_W × 1000) = 10 × log10(P_mW). For example, 1 W = 10 × log10(1000) = 30 dBm. 100 mW = 10 × log10(100) = 20 dBm.

What is 1 watt in dBm?

1 W equals 30 dBm, because 1 W = 1000 mW and 10 × log10(1000) = 30.

What is 0.001 W (1 mW) in dBm?

1 mW equals 0 dBm by definition, since dBm is referenced to 1 milliwatt and log10(1) = 0.

Why use dBm instead of watts?

dBm compresses the enormous dynamic range of RF power (from femtowatts to kilowatts) into a manageable numeric scale. Gains and losses also become simple additions and subtractions on the dBm scale rather than multiplications.

Can I convert negative dBm to watts?

Yes. Negative dBm values represent power below 1 mW but are still positive physical power levels. For example, −10 dBm = 10^(−10/10) mW = 0.1 mW = 0.0001 W.

What is the difference between dBm and dBW?

dBm is referenced to 1 milliwatt; dBW is referenced to 1 watt. dBW = dBm − 30. For example, 30 dBm = 0 dBW = 1 W.

Watts to dBm Calculator

Name: Watts to dBm Calculator
Availability: InStock
Author: Nham Vu

Enter power in watts or milliwatts and instantly get the equivalent dBm value using the standard logarithmic formula.

Power Converter

Power in Watts

Power in Milliwatts

or enter dBm

Power in dBm

dBm

Conversion Results

Enter a value on the left to see results.

Common Power Level Reference

Watts	Milliwatts	dBm	Typical Use
1×10⁻⁹	0.000001	−60	Typical Wi-Fi receive sensitivity
0.000001	0.001	−30	Bluetooth receive threshold
0.001	1	0	Reference level (1 mW)
0.01	10	10	Bluetooth class 1 transmitter
0.1	100	20	Wi-Fi access point output
1	1,000	30	Consumer cordless phone
10	10,000	40	Handheld radio transmitter
1,000	1,000,000	60	Commercial broadcast station

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Summary

Enter power in watts or milliwatts and instantly get the equivalent dBm value using the standard logarithmic formula.

How it works

Enter a power value in watts or milliwatts in the input field.
The tool applies the formula dBm = 10 × log10(P_mW) and shows the result instantly.
Alternatively, enter a dBm value to reverse-convert to watts and milliwatts.
Click any result card to copy the value to your clipboard.
Click any row in the reference table to load that power level automatically.

Use cases

Convert transmitter output power from watts to dBm for link budget analysis.
Express antenna gain or amplifier output in dBm for RF system design.
Convert receiver sensitivity thresholds from watts to dBm.
Translate power meter readings between linear and logarithmic scales.
Calculate signal levels for Wi-Fi, LTE, and Bluetooth systems.
Verify power levels in coaxial cable and fiber-optic link budgets.
Convert lab instrument power readings to dBm for documentation.

Frequently Asked Questions

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Last updated: 2026-05-29 · Reviewed by Nham Vu