dbm to db calculator

Convert a power level in dBm to a relative level in dB by selecting a reference level. Since dB is a ratio, a reference is required.

Power Level (dBm)

Reference Level (dBm)

Quick examples:

What this calculator does

This tool finds the difference between two power levels expressed in dBm. The output is a relative value in dB. In simple terms:

dBm = absolute power level referenced to 1 milliwatt.
dB = relative change (gain or loss) between two levels.

So if you enter 10 dBm and compare it to 0 dBm, the result is +10 dB.

Important: You cannot convert dBm to dB without defining what you are comparing against. This calculator uses a reference level that you choose.

dBm vs dB (quick explanation)

dBm is absolute

dBm tells you the actual power level relative to 1 mW. Example: 0 dBm = 1 mW, 10 dBm = 10 mW, 20 dBm = 100 mW.

dB is relative

dB only tells you how much one signal differs from another. Example: +3 dB means roughly double the power, -3 dB means roughly half the power.

Formulas used

dB difference = dBm(input) - dBm(reference)

Power (mW) = 10^{(dBm / 10)}

The calculator also shows both levels in milliwatts and their ratio, which can be useful for RF engineering, wireless link budgets, and audio signal chains.

Worked examples

Example 1: -50 dBm compared to -60 dBm

Difference = -50 - (-60) = +10 dB. The -50 dBm signal is 10 dB stronger (10x power ratio).

Example 2: 30 dBm compared to 0 dBm

Difference = 30 - 0 = +30 dB. This is a 1000x power ratio.

Example 3: -3 dBm compared to 0 dBm

Difference = -3 - 0 = -3 dB. This is close to half power (about 0.5x).

Common use cases

Comparing received signal levels in Wi‑Fi, LTE, and RF systems.
Finding gain/loss across amplifiers, cables, filters, and antennas.
Estimating margin in communication links.
Translating transmitter power changes into relative dB steps.

Quick reference table

dBm	Power (mW)	Relative to 0 dBm
-30	0.001 mW	-30 dB
-20	0.01 mW	-20 dB
-10	0.1 mW	-10 dB
0	1 mW	0 dB
10	10 mW	+10 dB
20	100 mW	+20 dB
30	1000 mW (1 W)	+30 dB

FAQ

Is dBm the same as dB?

No. dBm is an absolute unit (referenced to 1 mW). dB is just a ratio between two values.

Can I convert dBm directly to dB?

Only if you specify a reference. If your reference is 0 dBm, then the numeric value is the same.

Why are negative dBm values common?

Many received signals are less than 1 mW, so they appear as negative dBm values, especially in wireless receivers.