How do you get watts from dBm?
P (W) = 10^(dBm / 10) ÷ 1000. For example 13 dBm is 10^1.3 = 19.95 mW, or 0.01995 W. Going the other way, dBm = 10 × log10(P / 1 mW).
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dBm to watts converter
Convert dBm to watts and back, along with dBW and milliwatts, and see the RMS, peak and peak-to-peak voltage, current and dBµV that power makes in 50 Ω, 75 Ω or any impedance. This dBm calculator starts from a power, a voltage read on a scope, or a spectrum analyzer level.
Convert from
Examples
dBm
Decibels relative to 1 mW. Negative below 1 mW.
Ω
50 Ω for RF, 75 Ω for video and cable TV, 600 Ω for audio.
Power
1 mW
- Power in dBW
- -30 dBW
- RMS voltage in 50 Ω
- 223.61 mV
- Peak voltage (sine)
- 316.23 mV
- Peak-to-peak voltage (sine)
- 632.46 mV
- RMS current
- 4.4721 mA
- Level in dBµV (50 Ω)
- 106.99 dBµV
- Level in dBmV
- 46.99 dBmV
- Level in dBV
- -13.01 dBV
dBm, dBW and watts do not depend on impedance; the voltages, current and dBµV do. They assume a resistive 50 Ω load and an unmodulated sine wave.
1 mW (0 dBm) in other impedances
| Impedance | RMS voltage | Peak-to-peak (sine) | dBµV |
|---|---|---|---|
| 50 Ω | 223.6 mV | 632.5 mV | 106.99 dBµV |
| 75 Ω | 273.9 mV | 774.6 mV | 108.75 dBµV |
| 600 Ω | 774.6 mV | 2.191 V | 117.78 dBµV |
How do you convert dBm to watts?
Use P (W) = 10^(dBm ÷ 10) ÷ 1000. 0 dBm is 1 mW, 10 dBm is 10 mW, 20 dBm is 100 mW and 30 dBm is 1 W. In a 50 Ω system 0 dBm is 223.6 mV rms (632.5 mV peak-to-peak for a sine), and the reverse is dBm = 10 × log10(P ÷ 1 mW).
dBm to watts formula, plus dBm to volts
dBm is power in decibels relative to one milliwatt. Converting to voltage needs the impedance the power is delivered into, and peak values assume a sine wave.
P = 10^(dBm ÷ 10) ÷ 1000 dBm = 10 × log10(P ÷ 1 mW) dBW = dBm − 30
- P
- power in watts
- Z
- resistive load or system impedance in Ω (50 Ω for most RF)
- Vrms, Vpk, Vpp
- RMS, peak and peak-to-peak voltage of a sine wave
Vrms = √(P × Z) Vpk = √2 × Vrms Vpp = 2√2 × Vrms
dBµV = 20 × log10(Vrms ÷ 1 µV) = dBm + 90 + 10 × log10(Z)
Worked examples
Example 1: a 13 dBm oscillator
P = 10^(13 ÷ 10) ÷ 1000 = 19.95 mW. Into 50 Ω, Vrms = √(0.01995 × 50) = 998.8 mV, so 13 dBm is the familiar “about 1 V rms in 50 Ω”. On a scope the sine is 2.825 V peak-to-peak.
Example 2: a 100 W transmitter
dBm = 10 × log10(100 W ÷ 1 mW) = 50 dBm, or 20 dBW. Into a 50 Ω antenna that is 70.71 V rms and 100 V peak, which is why connectors and attenuators carry voltage ratings as well as power ratings.
Example 3: a spectrum analyzer reading in dBµV
60 dBµV is 1 mV rms. In 50 Ω that delivers 20 nW, which is −46.99 dBm. The shortcut gives the same answer: dBm = dBµV − 106.99 in 50 Ω.
dBm to watts table (−30 to +50 dBm)
Power, RMS voltage and peak-to-peak voltage of a sine wave in a 50 Ω system.
| dBm | dBW | Power | Vrms (50 Ω) | Vpp (50 Ω, sine) | dBµV (50 Ω) |
|---|---|---|---|---|---|
| −30 dBm | −60 dBW | 1 µW | 7.071 mV | 20 mV | 76.99 dBµV |
| −20 dBm | −50 dBW | 10 µW | 22.36 mV | 63.25 mV | 86.99 dBµV |
| −10 dBm | −40 dBW | 100 µW | 70.71 mV | 200 mV | 96.99 dBµV |
| −3 dBm | −33 dBW | 501 µW | 158.3 mV | 447.7 mV | 103.99 dBµV |
| 0 dBm | −30 dBW | 1 mW | 223.6 mV | 632.5 mV | 106.99 dBµV |
| 3 dBm | −27 dBW | 2 mW | 315.9 mV | 893.4 mV | 109.99 dBµV |
| 6 dBm | −24 dBW | 3.98 mW | 446.2 mV | 1.262 V | 112.99 dBµV |
| 10 dBm | −20 dBW | 10 mW | 707.1 mV | 2 V | 116.99 dBµV |
| 13 dBm | −17 dBW | 20 mW | 998.8 mV | 2.825 V | 119.99 dBµV |
| 17 dBm | −13 dBW | 50.1 mW | 1.583 V | 4.477 V | 123.99 dBµV |
| 20 dBm | −10 dBW | 100 mW | 2.236 V | 6.325 V | 126.99 dBµV |
| 23 dBm | −7 dBW | 200 mW | 3.159 V | 8.934 V | 129.99 dBµV |
| 27 dBm | −3 dBW | 501 mW | 5.006 V | 14.16 V | 133.99 dBµV |
| 30 dBm | 0 dBW | 1 W | 7.071 V | 20 V | 136.99 dBµV |
| 33 dBm | 3 dBW | 2 W | 9.988 V | 28.25 V | 139.99 dBµV |
| 37 dBm | 7 dBW | 5.01 W | 15.83 V | 44.77 V | 143.99 dBµV |
| 40 dBm | 10 dBW | 10 W | 22.36 V | 63.25 V | 146.99 dBµV |
| 43 dBm | 13 dBW | 20 W | 31.59 V | 89.34 V | 149.99 dBµV |
| 47 dBm | 17 dBW | 50.1 W | 50.06 V | 141.6 V | 153.99 dBµV |
| 50 dBm | 20 dBW | 100 W | 70.71 V | 200 V | 156.99 dBµV |
0 dBm in common reference impedances
The same 1 mW gives a different voltage in each impedance. 50 Ω is the RF standard, 75 Ω is used for video and cable TV, and 600 Ω is the old telephone and audio reference.
| Impedance | Vrms at 0 dBm | Vpp at 0 dBm (sine) | dBµV at 0 dBm | dBm at 1 V rms |
|---|---|---|---|---|
| 50 Ω | 223.6 mV | 632.5 mV | 106.99 dBµV | 13.01 dBm |
| 60 Ω | 244.9 mV | 692.8 mV | 107.78 dBµV | 12.22 dBm |
| 75 Ω | 273.9 mV | 774.6 mV | 108.75 dBµV | 11.25 dBm |
| 600 Ω | 774.6 mV | 2.191 V | 117.78 dBµV | 2.218 dBm |
Where the conversion stops being exact
The voltage columns assume an unmodulated sine wave in a matched, resistive load. Modulated signals have a higher peak voltage than a sine of the same average power: noise-like signals such as OFDM have crest factors around 11 dB, so check the peak envelope power, not just the average dBm, against an amplifier’s or analyzer’s maximum input. A mismatched load reflects part of the power, so the voltage at the connector is no longer √(P × Z). And a source with a 50 Ω output impedance driving an oscilloscope’s 1 MΩ input is effectively unloaded, so the scope can read up to twice the voltage it would develop across 50 Ω. Use the scope’s 50 Ω input or a feed-through terminator when you compare against a dBm figure.
Glossary
- dBm
- Power in decibels relative to 1 mW. 0 dBm = 1 mW, 30 dBm = 1 W.
- dBW
- Power in decibels relative to 1 W. dBW = dBm − 30.
- dBµV
- RMS voltage in decibels relative to 1 µV. 120 dBµV = 1 V.
- dBmV
- RMS voltage in decibels relative to 1 mV, common on 75 Ω cable systems.
- RMS voltage
- The voltage that delivers the same average power to a resistor as a DC voltage of that value.
- Peak-to-peak voltage
- The span from the most negative to the most positive point; 2√2 times the RMS value for a sine.
- Characteristic impedance
- The impedance a system is built around: 50 Ω for most RF, 75 Ω for video and cable TV.
Related guides
- Decibel (dB) calculator: ratios, cascaded gains and adding levels.
- RMS voltage calculator: peak, peak-to-peak and RMS for other waveforms.
Frequently asked questions
How do you convert watts to dBm?
dBm = 10 × log10(P ÷ 1 mW). For example 100 W is 10 × log10(100 W ÷ 1 mW) = 50 dBm, and 1 W is 30 dBm.
How do you convert dBm to mW?
mW = 10^(dBm ÷ 10), so 0 dBm is exactly 1 mW and 13 dBm is 19.95 mW. Going the other way, dBm = 10 × log10(mW).
What is 0 dBm in watts and volts?
0 dBm is exactly 1 mW. Across 50 Ω that is 223.6 mV rms, 316.2 mV peak or 632.5 mV peak-to-peak for a sine wave, and 106.99 dBµV.
How many watts is 30 dBm?
30 dBm is 1 W. Every 10 dB is a factor of ten: 20 dBm is 100 mW, 40 dBm is 10 W and −30 dBm is 1 µW. Every 3 dB is roughly a factor of two, so 33 dBm is about 2 W.
How do you convert dBm to dBW?
Subtract 30: dBW = dBm − 30, because 1 W is 1000 mW and 10 × log10(1000) = 30. So 30 dBm is 0 dBW, and 0 dBm is −30 dBW.
How do you convert dBW to watts?
Add 30 to get dBm, then use the dBm formula. 20 dBW is 50 dBm, which is 100 W.
Does dBm depend on impedance?
No. dBm is a power level, so it is the same in any impedance. The voltage it produces does depend on impedance: 0 dBm is 223.6 mV rms in 50 Ω, 273.9 mV in 75 Ω and 774.6 mV in 600 Ω.
How do you convert dBm to dBµV?
dBµV = dBm + 90 + 10 × log10(Z). In 50 Ω that is dBm + 106.99; in 75 Ω it is dBm + 108.75. A spectrum analyzer reading of −40 dBm in 50 Ω is 66.99 dBµV.
How do I convert dBm to Vpp (peak-to-peak voltage)?
Find the RMS voltage, Vrms = √(P × Z), then multiply by 2√2 for a sine: Vpp = 2√2 × Vrms. 10 dBm in 50 Ω is 707.1 mV rms and 2 V peak-to-peak. Modulated signals have higher peaks for the same average power.
What is 0 dBmV in dBm on a 75 Ω cable system?
0 dBmV is 1 mV rms. In 75 Ω that is 13.33 nW, or −48.75 dBm.
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Sources
- Keysight AN 1449-1, Fundamentals of RF and Microwave Power Measurements, Part 1 (definition of dBm, Eq. 2-2)
- Rohde & Schwarz Application Note 1MA98, dB or not dB? (dBm, dBµV, reference impedances in Table 6-3, crest factor in §5.10)
- NIST SP 811 (2008), Guide for the Use of the SI, §8.7: levels of power and field quantities
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