dBm to Watts Converter – dBm, dBW, W, mW

Converter

Convert dBm to watts and watts to dBm

Type a value on either side, or in any field below. Every other unit follows at once, so the converter works in both directions: dBm to watts and watts to dBm, dBW to mW, dBm to dBµV and back.

Converter type on either side

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Power in decibels 10·log₁₀(P / reference)

dBm = 1 mW, dBW = 1 W, dBk = 1 kW, dBµW = 1 µW, dBpW = 1 pW, dBf = 1 fW reference.

Linear power

Very large or very small values switch to e-notation: 2.5e-9 W is 2.5 nW.

Voltage and current across the load impedance, sine wave

Impedance

Significant digits

Where this power sits logarithmic scale, dBm

Reference levels are typical values for orientation. Thermal noise is −174 dBm in 1 Hz at 290 K; add 10·log₁₀(bandwidth in Hz) for a wider bandwidth.

Reference

dBm to watts conversion table

A dBm to watts table for any range and step, with voltage and dBµV at the impedance chosen above. The row matching your converter value is highlighted.

From

dBm

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Theory — read the article Decibels, dBm, dBW and Watts Explained Why RF engineers work in decibels, how the references work, and how to read power, gain and loss in a link budget. Next step — check the exposure RF Exposure Calculator Turn your EIRP into power density and a compliance distance against FCC, ICNIRP and Safety Code 6 limits — free, in your browser.

Engineering Theory

Theory Behind the Conversions

The equations the converter uses. For the full background on decibels and why RF work is done in them, read the theory article on dBm, dBW and watts.

1. The Decibel Is a Ratio

A decibel expresses the ratio of two powers on a logarithmic scale. A ratio alone has no unit, so plain dB describes gain or loss. Adding a letter fixes the reference and turns the ratio into an absolute power: dBm is referenced to 1 milliwatt and dBW to 1 watt.

Power ratio in decibels

G = 10 \cdot \log_{10} (\frac{P_{2}}{P_{1}}) dB

2. dBm, dBW and Watts

Watts to dBm and dBW

P_{dBm} = 10 \cdot \log_{10} (\frac{P_{W}}{1 mW}), P_{dBW} = P_{dBm} - 30

dBm to watts

P_{W} = 10^{(P_{dBm} - 30) / 10}, P_{mW} = 10^{P_{dBm} / 10}

The other references follow the same pattern with a fixed offset: dBk = dBm − 60, dBµW = dBm + 30, dBpW = dBm + 90 and dBf = dBm + 120.

Table 1. Values worth memorising
dBm	dBW	Power	Typical example
−130	−160	0.1 fW	GPS signal at the ground
−90	−120	1 pW	Weak cellular signal
−60	−90	1 nW	Strong Wi-Fi signal
−30	−60	1 µW	Receiver overload region
0	−30	1 mW	Bluetooth Class 2, lab signal generator
20	−10	100 mW	Wi-Fi access point
30	0	1 W	Handheld radio
50	20	100 W	HF transceiver
60	30	1 kW	Linear amplifier
80	50	100 kW	FM broadcast ERP

3. Rules of Thumb

+3 dB doubles the power (exactly 3.0103 dB); −3 dB halves it.
+10 dB is ten times the power, +20 dB a hundred times, +30 dB a thousand times.
A gain or loss in dB is added to a level in dBm: 20 dBm through a 30 dB amplifier is 50 dBm.
Two levels in dBm are never added. 30 dBm + 30 dBm is 33 dBm, not 60 dBm.
dBm − dBm is a ratio in dB: 43 dBm − 40 dBm = 3 dB.

4. Power, Voltage and Impedance

Power into a resistive load fixes the voltage across it. For a sine wave the peak voltage is √2 times the RMS value and the peak-to-peak voltage twice the peak. Voltage decibels use 20·log₁₀ because power goes with the square of voltage.

RMS voltage and current

V_{rms} = \sqrt{P \cdot Z}, I_{rms} = \sqrt{P / Z}, V_{pp} = 2 \sqrt{2} \cdot V_{rms}

dBm to dBµV

V_{dBµV} = P_{dBm} + 90 + 10 \cdot \log_{10} (Z)

dBm + 107.0 at 50 Ω, dBm + 108.75 at 75 Ω. dBmV = dBµV − 60, dBV = dBµV − 120.

5. Adding Signals

Signals on different frequencies, and noise, add in power. Signals on the same frequency in phase add in voltage, which gives four times the power for two equal signals (+6.02 dB) instead of twice (+3.01 dB).

Sum of powers in dBm

P_{total, dBm} = 10 \cdot \log_{10} (\sum_{i} 10^{P_{i} / 10})

Frequently Asked Questions

Common questions about dBm, dBW, watts and decibel arithmetic.

How do I convert dBm to watts?

P(W) = 10^((dBm − 30)/10). For example 30 dBm is 1 W, 40 dBm is 10 W and 50 dBm is 100 W. In milliwatts, P(mW) = 10^(dBm/10).

How do I convert watts to dBm?

dBm = 10·log10(P / 1 mW) = 10·log10(P in watts) + 30. For example 5 W is 36.99 dBm and 100 mW is 20 dBm.

What is the difference between dBm and dBW?

Both are power in decibels. dBm is referenced to 1 milliwatt and dBW to 1 watt, so dBW = dBm − 30. 0 dBW is 1 W, which is 30 dBm.

Can dBm be negative?

Yes. Negative dBm means less than 1 mW. Received radio signals are almost always negative: −70 dBm is 100 picowatts and a GPS signal at the ground is about −130 dBm, or 0.1 femtowatt.

How do I convert dBm to dBµV?

dBµV = dBm + 90 + 10·log10(Z). In a 50 Ω system that is dBm + 107.0, and in a 75 Ω system dBm + 108.75. The converter handles any impedance.

Can I add dBm values together?

No. Convert each to watts, add, and convert back. Two equal signals add up to 3.01 dB more than one, not double the dBm value. You can add a dB gain or subtract a dB loss from a dBm level directly.

What does +3 dB and +10 dB mean in power?

+3 dB is about twice the power (exactly 3.0103 dB), +10 dB is ten times, +20 dB a hundred times. −3 dB is half and −10 dB a tenth.

What is dBf?

dBf is power referenced to 1 femtowatt (10^−15 W), used for FM tuner sensitivity. dBf = dBm + 120.

How many watts is 0 dBm?

0 dBm is exactly 1 milliwatt, or 0.001 W. Every 10 dB above that multiplies the power by ten: 10 dBm is 10 mW, 20 dBm is 100 mW and 30 dBm is 1 W.

What is 50 dBm in watts?

50 dBm is 100 W, from P(W) = 10^((50 − 30)/10) = 10^2 = 100 W. 47 dBm is about 50 W and 53 dBm about 200 W.

What is the difference between dBm, dBi and dBd?

dBm is an absolute power referenced to 1 mW. dBi and dBd are antenna gains, ratios referenced to an isotropic antenna and a half-wave dipole, with dBi = dBd + 2.15. A gain in dBi or dBd is added to a level in dBm but cannot be converted to watts.

About this dBm to watts converter

This free converter from NextAntennas changes RF power between decibel units (dBm, dBW, dBk, dBµW, dBpW, dBf) and linear units (W, kW, MW, mW, µW, nW, pW, fW) in either direction, and gives the matching RMS, peak and peak-to-peak voltage, dBV, dBmV, dBµV and current at 50, 75, 300, 600 Ω or any impedance you enter.

How to use it

Convert: type a value on either side of the converter, or in any unit field. Every other unit updates as you type.
Voltage: pick the impedance to see RMS, peak and peak-to-peak voltage, dBµV and current for the same power.
Conversion table: print a dBm to watts table for any range and copy it as CSV.

For the background, read the theory article on decibels, dBm, dBW and watts. More RF tools: RF exposure calculator · microstrip patch antenna calculator · dipole & monopole antenna calculator · microstrip line calculator · all NextAntennas calculators.