dBm to Watts Converter (Decibels)
Decibels to watts, ratios, volts and pascals, with the reference behind every dB.
Type a level in plain words — “23 dBm to W”, “0.5 W in dBm”, “−6 dB”, “+4 dBu to V”, “94 dB SPL to Pa” — or use the boxes below.
Exact · W = 0.001 × 10^(dBm ÷ 10) · 0 dBm = 1 mW
- 100 mW = 20 dBm. Every +3 dB about doubles the power; every +10 dB multiplies it by 10.
- dBm (dB re 1 mW): 0 dBm = 1 mW: L = 10 × lg(P ÷ 1 mW)
- Watt: the SI unit of power
20 dBm in every unit
Select a unit to convert to it. Values marked ≈ are rounded.
| Unit | Value | Copy |
|---|---|---|
| from | 20 | |
| −10 | ||
| −40 | ||
| 50 | ||
| 100,000,000,000 | ||
| 100,000,000 | ||
| 100,000 | ||
| 100 | ||
| to | 0.1 | |
| 0.0001 | ||
| 1 × 10⁻⁷ |
dBm to milliwatts and watts
Common values of the quantity above, rounded to 4 significant digits (decibels to 0.01).
| dBm | mW | W | dBW |
|---|---|---|---|
| −90 | 1 × 10⁻⁹ | 1 × 10⁻¹² | −120 |
| −80 | 1 × 10⁻⁸ | 1 × 10⁻¹¹ | −110 |
| −70 | 1 × 10⁻⁷ | 1 × 10⁻¹⁰ | −100 |
| −60 | 0.000001 | 1 × 10⁻⁹ | −90 |
| −50 | 0.00001 | 1 × 10⁻⁸ | −80 |
| −40 | 0.0001 | 1 × 10⁻⁷ | −70 |
| −30 | 0.001 | 0.000001 | −60 |
| −20 | 0.01 | 0.00001 | −50 |
| −10 | 0.1 | 0.0001 | −40 |
| 0 | 1 | 0.001 | −30 |
| 3 | ≈ 1.995 | ≈ 0.001995 | −27 |
| 6 | ≈ 3.981 | ≈ 0.003981 | −24 |
| 10 | 10 | 0.01 | −20 |
| 13 | ≈ 19.95 | ≈ 0.01995 | −17 |
| 17 | ≈ 50.12 | ≈ 0.05012 | −13 |
| 20 | 100 | 0.1 | −10 |
| 23 | ≈ 199.5 | ≈ 0.1995 | −7 |
| 27 | ≈ 501.2 | ≈ 0.5012 | −3 |
| 30 | 1,000 | 1 | 0 |
| 33 | ≈ 1,995 | ≈ 1.995 | 3 |
| 37 | ≈ 5,012 | ≈ 5.012 | 7 |
| 40 | 10,000 | 10 | 10 |
| 50 | 100,000 | 100 | 20 |
| 60 | 1,000,000 | 1,000 | 30 |
Levels, ratios and impedance
- A plain dB value is a ratio (a gain or a loss). A dB with a suffix — dBm, dBW, dBV, dBu, dB SPL — is a level against a stated reference, so it is an amount.
- Power and voltage levels meet only through an impedance: P = U² ÷ R. At 50 Ω, 0 dBm is 0.2236 V or about 107 dBµV; at 600 Ω it is 0.7746 V, which is why 0 dBm and 0 dBu coincide there. The Decibel Calculator converts them at any impedance, adds levels and works out VSWR.
- Sound: dB SPL in air is against 20 µPa and underwater levels against 1 µPa; a machine’s sound power level (re 1 pW) is what it radiates, not the level you hear.
About the dBm to Watts Converter (Decibels)
Convert decibel levels into the amounts they stand for and back: dBm, dBW, dBk and dBµW to watts, milliwatts and microwatts; dB, bels and nepers to power and amplitude ratios; dBV, dBu, dBmV and dBµV to volts; dB SPL (and dB re 1 µPa under water) to pascals; and sound power levels to watts. Type in either box and the other updates, the table lists the value in every unit of its kind, and Quick convert reads text such as 23 dBm to W or +4 dBu to V.
Every result shows its formula and the reference behind the decibels — 1 mW for dBm, 1 W for dBW, 1 V for dBV, 0.7746 V for dBu, 1 µV for dBµV, 20 µPa for dB SPL — so you can check it by hand.
How to use it
- Pick the quantity — Power, Ratio, Voltage, Sound pressure or Sound power — or type
23 dBm to Win Quick convert and press Enter. - Type the number in From and pick its unit, then the unit you want in To. Typing in To converts the other way.
- Read the result with its formula and reference, and the table of every unit; select a unit in the table to convert to it.
- Copy the result or a link, copy the table or download it as CSV, and look up common values in the chart below.
Examples
20 dBm to W
0.1 W (100 mW)
0.5 W to dBm
≈ 26.99 dBm
10 × lg(0.5 W ÷ 1 mW) = 10 × lg 500.
−30 dBm to µW
1 µW
3 dB
≈ 1.995 × the power, ≈ 1.413 × the voltage
A plain dB is a ratio: 10^(3 ÷ 10) for power, 10^(3 ÷ 20) for voltage.
+4 dBu to V
≈ 1.228 V rms
0 dBu = √0.6 V ≈ 0.7746 V, the voltage that puts 1 mW into 600 Ω.
60 dBµV to mV
1 mV (0 dBmV)
94 dB SPL to Pa
≈ 1.002 Pa
1 Pa is 93.98 dB SPL: 20 × lg(1 Pa ÷ 20 µPa).
1 Np to dB
≈ 8.686 dB
Common uses
- RF and wireless: transmitter power, receiver sensitivity and link budgets in dBm, dBW and watts.
- Audio: line levels in dBu and dBV, gains and losses in dB.
- Cable TV and antennas: signal levels in dBmV and dBµV.
- Acoustics: sound pressure levels in dB SPL and pascals, and sound power levels in watts.
- Physics and electronics homework with dB, bels and nepers.
The formulas
- Power levels: L = 10 × lg(P ÷ P₀) and P = P₀ × 10^(L ÷ 10). Every +10 dB multiplies the power by 10, and +3 dB about doubles it (10 × lg 2 = 3.0103).
- Field levels (voltage, current, sound pressure): L = 20 × lg(U ÷ U₀) and U = U₀ × 10^(L ÷ 20), because power goes with the square of the field: +6 dB about doubles a voltage.
- Nepers use the natural logarithm of a field ratio: 1 Np = 20 × lg e ≈ 8.686 dB, and 1 dB ≈ 0.1151 Np. A bel is 10 dB.
These are the definitions of Recommendation ITU-R V.574, Use of the decibel and the neper in telecommunications, and of IEC 60027-3 (logarithmic quantities and units).
The reference behind each level
- dBm: 1 mW. dBW: 1 W (0 dBW = 30 dBm). dBk: 1 kW. dBµW: 1 µW.
- dBV: 1 V rms. dBmV: 1 mV. dBµV: 1 µV (0 dBV = 60 dBmV = 120 dBµV).
- dBu: √0.6 V ≈ 0.7746 V rms, the voltage that dissipates 1 mW in 600 Ω, so 0 dBu = −2.218 dBV. ITU-R V.574 writes the reference as 0.775 V, about 0.005 dB higher.
- dB SPL: 20 µPa in air (ITU-R V.574 § 6.8; the reference values of acoustics are standardised in ISO 1683). Under water levels are given re 1 µPa, which makes the same pressure 26.02 dB higher. Sound power level: 1 pW.
A plain dB has no reference at all: it is a ratio, a gain or a loss.
Power, voltage and impedance
A power level and a voltage level describe the same signal only through the impedance it flows into: P = U² ÷ R. At 50 Ω, 0 dBm (1 mW) is 0.2236 V rms, about 107 dBµV; at 75 Ω it is 0.2739 V; at 600 Ω it is 0.7746 V — which is why 0 dBm and 0 dBu coincide there. This converter keeps power and voltage apart; the Decibel Calculator converts between them at any impedance, adds levels and works out VSWR and return loss.
Limitations
- Voltage levels are rms values; the peak and peak-to-peak line assumes a sine wave.
- Power and voltage levels are not converted into each other here, because that needs the impedance.
- dB(A) and dB(C) convert to the frequency-weighted pressure: the weighting itself is not undone.
- A sound power level is what a source radiates; the sound pressure you hear depends on the distance and the room, so the two are not converted into each other.
- Results are rounded for display; Full precision shows 12 significant digits.
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Frequently asked questions
How do I convert dBm to watts?
P = 1 mW × 10^(dBm ÷ 10), or in watts 10^(dBm ÷ 10) ÷ 1,000. So 0 dBm = 1 mW, 10 dBm = 10 mW, 20 dBm = 100 mW and 30 dBm = 1 W; −30 dBm = 1 µW. The other way, dBm = 10 × lg(P ÷ 1 mW).
How many dBm is 1 watt?
30 dBm: 1 W is 1,000 mW, and 10 × lg 1,000 = 30. It is also 0 dBW, and 2 W is about 33 dBm.
What is the difference between dB and dBm?
A dB is a ratio: a 3 dB gain doubles a power, whatever it is. A dBm is a level against 1 mW, so it is an amount of power: 3 dBm is about 2 mW. Adding dB to a dBm level gives another dBm level (20 dBm + 3 dB = 23 dBm).
What is the difference between dBu and dBV?
Only the reference: dBV is relative to 1 V rms and dBu to 0.7746 V rms. The same voltage is 2.218 dB higher in dBu than in dBV, so +4 dBu is 1.228 V and −10 dBV is 0.316 V.
Why is 3 dB double?
Because 10 × lg 2 = 3.0103: doubling a power adds about 3 dB, and halving it takes 3 dB away. For voltages it takes about 6 dB to double, since power goes with the voltage squared.
How do I convert dB SPL to pascals?
p = 20 µPa × 10^(L ÷ 20). So 94 dB SPL ≈ 1 Pa and 114 dB SPL ≈ 10 Pa; 0 dB SPL is the 20 µPa reference itself. Sound levels are often quoted as a plain “dB”, so Quick convert reads 94 dB to Pa or 1 Pa in dB as dB SPL and says so.
Can I convert dBm to volts or dBµV?
Only with the impedance, because P = U² ÷ R. At 50 Ω, 0 dBm is 0.2236 V or about 107 dBµV. Use the Decibel Calculator, which converts power and voltage levels at 50 Ω, 75 Ω, 600 Ω or any impedance.