RF & Power Conversion Tool

dBm ↔ Watts Calculator

Convert absolute RF and electrical power levels between dBm, mW and watts. Enter a dBm value to calculate its equivalent power, or enter watts/milliwatts to calculate the corresponding dBm level.

dBm Power Converter

Convert between dBm, milliwatts and watts instantly.

dBm
Absolute power referenced to 1 mW
Converted Power
1 W
1000 mW
dBm +30 dBm
mW 1000 mW
W 1 W

P(W) = 10^((dBm − 30) / 10)

dBm Conversion Formulas

dBm is an absolute power measurement referenced to 1 milliwatt. Because the reference is fixed, dBm can be converted directly into an absolute power in mW or watts.

dBm → mW

P(mW) = 10dBm/10

To convert a dBm level into milliwatts, raise 10 to the dBm value divided by 10.

For example:

20 dBm = 10² mW = 100 mW

dBm → Watts

P(W) = 10(dBm−30)/10

Since 1 W equals 1000 mW and 1000 mW is 30 dB above 1 mW, subtract 30 from the dBm value before dividing by 10.

30 dBm = 1 W

Watts → dBm

dBm = 10 log₁₀(P(W) × 1000)

Convert watts to milliwatts and then calculate the logarithm relative to 1 mW.

dBm = 10 log₁₀(P(mW))
Reference point: dBm is referenced specifically to 1 mW. Therefore, 1 mW = 0 dBm, 10 mW = 10 dBm, 100 mW = 20 dBm and 1 W = 30 dBm.

Common dBm to Watts Values

These reference values are useful when working with RF transmitters, receivers, wireless equipment, amplifiers, attenuators and laboratory instruments.

dBm Power Watts Typical Interpretation
-40 dBm 0.0001 mW 100 nW Very low signal level
-30 dBm 0.001 mW 1 µW Low RF power
-20 dBm 0.01 mW 10 µW Low RF power
-10 dBm 0.1 mW 100 µW Below 1 mW
0 dBm 1 mW 0.001 W Reference power
10 dBm 10 mW 0.01 W 10× reference power
20 dBm 100 mW 0.1 W 100× reference power
30 dBm 1000 mW 1 W 1 watt
40 dBm 10000 mW 10 W 10 watts
50 dBm 100000 mW 100 W 100 watts

Understanding the dBm Scale

Negative dBm

Negative dBm values represent power levels below 1 mW. For example, -10 dBm is 0.1 mW and -30 dBm is 1 µW.

0 dBm

0 dBm is exactly 1 mW. This is the fixed reference used by the dBm unit.

Positive dBm

Positive dBm values represent power above 1 mW. Every increase of 10 dB corresponds to a tenfold increase in power.

+10 dB = 10× power   •   +20 dB = 100× power   •   +30 dB = 1000× power

Worked dBm Conversion Examples

Example 1: 30 dBm to Watts

Convert a 30 dBm RF power level to watts.

P(W) = 10(30−30)/10
P(W) = 10⁰ = 1 W

Therefore, 30 dBm = 1 W.

Example 2: 20 dBm to mW

Convert 20 dBm into milliwatts.

P(mW) = 1020/10
P(mW) = 10² = 100 mW

Therefore, 20 dBm = 100 mW = 0.1 W.

Example 3: 100 mW to dBm

Convert 100 mW to dBm.

dBm = 10 log₁₀(100)
dBm = 20 dBm

Therefore, 100 mW = 20 dBm.

Example 4: 10 W to dBm

Convert a 10 W transmitter output to dBm.

dBm = 10 log₁₀(10 × 1000)
dBm = 40 dBm

Therefore, 10 W = 40 dBm.

dBm Applications in Electronics

dBm is especially useful when working with absolute RF and communications power levels.

RF Transmitters

Express transmitter output power in a logarithmic unit that is convenient for RF system calculations.

Wireless Networks

Compare received signal levels, transmitter power, path losses and antenna-system levels.

RF Components

Work with amplifier gain, filter insertion loss, attenuator values and RF measurement equipment.

Signal Measurements

Convert spectrum-analyzer, signal-generator and RF power-meter readings between dBm and watts.

Practical dBm Notes

dBm Is Absolute

Unlike plain dB, dBm represents an absolute power level because its reference is fixed at 1 mW.

dBm Can Be Negative

Negative dBm values are normal in RF systems. They simply indicate power below the 1 mW reference.

Logarithmic Scaling

Increasing power by 10× increases the dBm value by 10 dB. Increasing power by 100× increases it by 20 dB.

dBm vs dB: dBm is an absolute power level referenced to 1 mW. Plain dB expresses a ratio between two quantities and has no absolute reference by itself. For example, an amplifier can have +20 dB gain while its actual output power could be expressed separately in dBm.
dBm vs dBW: dBW uses 1 watt as its reference instead of 1 milliwatt. Therefore, dBm = dBW + 30 and dBW = dBm − 30.

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dBm ↔ Watts Calculator FAQ

Convert dBm to milliwatts using P(mW) = 10^(dBm/10), then divide by 1000 to obtain watts. Equivalently, P(W) = 10^((dBm - 30)/10).

Use dBm = 10 × log10(P(W) × 1000). The power must be positive because a logarithm cannot be calculated for zero or a negative power.

0 dBm equals 1 mW, which is 0.001 W.

10 dBm equals 10 mW, or 0.01 W.

20 dBm equals 100 mW, or 0.1 W.

30 dBm equals 1000 mW, which is 1 W.

1 W equals 30 dBm.

The m in dBm indicates a reference to 1 milliwatt. Therefore, dBm is an absolute power level referenced to 1 mW rather than a dimensionless power ratio.

Yes. Any power below 1 mW has a negative dBm value. For example, 0.1 mW equals -10 dBm and 0.01 mW equals -20 dBm.