dBm to Watts Converter

Convert dBm into watts and milliwatts with P(W) = 10^((dBm - 30)/10), or reverse a power in watts, milliwatts, or kilowatts back into dBm and dBW. It also reports the RMS and peak voltage that the power develops across a 50 or 75 ohm system impedance.

🔌Choose a Conversion Mode

🎯Real Power Level Presets

📝Power Inputs

Power level (dBm)

Decibels referenced to 1 milliwatt. Used in dBm to Watts mode.

Power value

Absolute power to convert into dBm. Used in reverse mode.

Power unit

Applies to the power value entered above.

System impedance R (ohm)

Load used to compute RMS and peak voltage from power.

Result significant figures

Controls rounding on every result card.

Voltage readout

Chooses which voltage figure fills the voltage card.

Power in Watts 1 W absolute power P(W)

Power in Milliwatts 1000 mW P(mW) = P(W) x 1000

Equivalent dBm 30 dBm and dBW alongside

Voltage at Load 7.071 V RMS across 50 ohm

🔢Formula Snapshot

mW10^(dBm/10)

W10^((dBm-30)/10)

dBm10 log10 mW

Vsqrt(P x R)

📋dBm to Watts Milestones

dBm	Power in mW	Power in Watts	Reads As
0 dBm	1 mW	0.001 W	1 milliwatt
10 dBm	10 mW	0.01 W	10 milliwatts
20 dBm	100 mW	0.1 W	Tenth watt
30 dBm	1000 mW	1 W	One watt
36 dBm	3981 mW	3.981 W	About 4 W
40 dBm	10000 mW	10 W	Ten watts
43 dBm	19953 mW	19.95 W	About 20 W
46 dBm	39811 mW	39.81 W	About 40 W
50 dBm	100000 mW	100 W	Hundred watts
60 dBm	1000000 mW	1000 W	One kilowatt

📊Decibel Step Reference

Change in dB	Power Ratio	Meaning	Example
+3 dB	2x	Power doubles	20 to 23 dBm
+6 dB	4x	Four times power	20 to 26 dBm
+10 dB	10x	Ten times power	20 to 30 dBm
+20 dB	100x	Hundred times	0 to 20 dBm
-3 dB	0.5x	Power halves	30 to 27 dBm
-10 dB	0.1x	One tenth power	30 to 20 dBm
0 dB	1x	No change	Same power

📡Real Transmit Power Levels

Device or Signal	Typical Power	In dBm	In Watts
Bluetooth Low Energy	1 mW	0 dBm	0.001 W
Zigbee radio	3.16 mW	5 dBm	0.00316 W
LoRa EU node	25 mW	14 dBm	0.025 W
Wi-Fi access point	100 mW	20 dBm	0.1 W
Mobile phone uplink	200 mW	23 dBm	0.2 W
Handheld ham radio	5 W	37 dBm	5 W
Mobile FM transceiver	50 W	47 dBm	50 W

📏Power and Voltage Unit Chain

Unit	Equals	In Watts	Note
1 kW	1000 W	1000 W	Kilowatt
1 W	1000 mW	1 W	Watt, 30 dBm
1 mW	0.001 W	0.001 W	Milliwatt, 0 dBm
1 µW	0.001 mW	0.000001 W	Microwatt, -30 dBm
1 dBW	30 dBm	varies	Ref 1 watt
1 dBm	0 dBW - 30	varies	Ref 1 mW

🗃dBm, Watts and Voltage Comparison Grid

dBm	dBW	Milliwatts	Watts	V RMS 50 ohm	V RMS 75 ohm
-30 dBm	-60 dBW	0.001 mW	0.000001 W	0.00707 V	0.00866 V
0 dBm	-30 dBW	1 mW	0.001 W	0.2236 V	0.2739 V
10 dBm	-20 dBW	10 mW	0.01 W	0.7071 V	0.8660 V
20 dBm	-10 dBW	100 mW	0.1 W	2.236 V	2.739 V
30 dBm	0 dBW	1000 mW	1 W	7.071 V	8.660 V
37 dBm	7 dBW	5012 mW	5.012 W	15.83 V	19.39 V
40 dBm	10 dBW	10000 mW	10 W	22.36 V	27.39 V
47 dBm	17 dBW	50119 mW	50.12 W	50.06 V	61.31 V
50 dBm	20 dBW	100000 mW	100 W	70.71 V	86.60 V
60 dBm	30 dBW	1000000 mW	1000 W	223.6 V	273.9 V

⚙Formula Breakdown

P(mW) = 10^(dBm/10)Power in milliwatts equals ten raised to the dBm value over ten. At 30 dBm that is 10^3 = 1000 mW.

P(W) = 10^((dBm-30)/10)Subtract 30 first because 1 W is 30 dBm. At 30 dBm, (30 - 30)/10 = 0, so P = 10^0 = 1 W.

P(W) = P(mW) / 1000Milliwatts and watts differ by a factor of 1000. So 1000 mW divided by 1000 equals 1 W.

dBm = 10 log10(P mW)Reverse direction from a power. For 1000 mW, dBm = 10 x log10(1000) = 10 x 3 = 30 dBm.

dBm = 10 log10(P W) + 30Convert watts straight to dBm. For 1 W, dBm = 10 x log10(1) + 30 = 0 + 30 = 30 dBm.

dBW = dBm - 30dBW uses a 1 watt reference. So 30 dBm equals 0 dBW, and 50 dBm equals 20 dBW.

V rms = sqrt(P x R)Voltage across a resistive load. For 1 W into 50 ohm, V = sqrt(1 x 50) = 7.071 V RMS.

V peak = V rms x sqrt 2Peak is the RMS value times 1.414. So 7.071 V RMS gives about 10 V peak into 50 ohm.

💡Practical Power Tips

Watch the 30 dBm boundary: The number 1 watt sits exactly at 30 dBm, so many regulatory limits are quoted there. A Wi-Fi radio at 20 dBm is 100 mW, a mobile phone at 23 dBm is 200 mW, and a 5 W handheld is about 37 dBm. Whenever you cross 30 dBm you are moving between the milliwatt world and the watt world, and every extra 10 dB multiplies power by ten.

Voltage depends on impedance: The same power makes a different voltage on 50 ohm versus 75 ohm. One watt into 50 ohm is 7.071 V RMS, but into 75 ohm it climbs to 8.660 V because V = sqrt(P x R). Peak voltage is 1.414 times higher again, so 100 W into 50 ohm reaches about 100 V peak. Size connectors, baluns, and attenuators for that peak, not just the average power.

This is the dBm to watts converter. The decibel-milliwatt scale is convenient as an engineer’s shorthand, particularly when specifying link budgets or the output of transmitters. Multiplication boils down to addition on a log scale. But when you see 30 dBm listed on a datasheet, it makes more sense if you understand it’s actualy a watt.

This calculator works in both directions and includes the dBW reference used by satellite engineers. And if you want to get all detailed, it will report peak and RMS voltage generated by that power across a realistic load.

How to Use the dBm to Watts Converter

A dBm (decibel measured relative to one milliwatt) is a decibel measurement that has a reference point for its zero value. In other words, dBm is not a unit for measuring ratios but for a specific absolute amount of power. DBm = 10 times the base-ten logarithm of the power in milliwatts. The difference between this conversion utility and just a simple decibel gain converter is that dBm refers to a specific power, a dB gain refers to a comparison of two powers.

For example, -3 dB on your dBm scale means that the power is about half a milliwatt or 0.5 mW. Every time you increase by ten on the dBm meter, the power increases ten times. This means 10 dBm is 10 mW, 20 dBm is 100 mW, and 30 dBm is one whole Watt.

To change dBm to watts, simply invert the log. Raising ten to the power of the dBm and multiplying by ten gives you the power in milliwatts. Subtracting thirty first gets you watts straight up. One watt is thirty dBm. Enter 30 dBm. The exponent will be zero and you have one watt. Enter 43 dBm (a popular amplifier rating). You’ll get roughly 19.95 watts. The calculator do that math for you so you don’t have to move the decimal point yourself.

To calculate the reverse, we accept inputs for power as a dBm number and convert it to kilowatts, watts, milliwatts or microwatts. We first normalize input to milliwatts. Next, we use the dBm formula to calculate output. For example, 37 dBm equates to a 5 watt handheld radio. 60 dBm is a 1 kilowatt broadcast stage. We flag negative or zero entries to keep the math honest on the low end, since a log of zero is not defined.

There are other notations on the calculator: dBm and dBW. DBm is referenced to one milliwatt (one millionth of a watt). DBW is referenced to one watt. Because one watt is one-thousand times larger than a milliwatt, there is a 30-dB difference between the two scales. In other words, dBW = dBm. 30. Zero dBW is -30 dBm. This is why satellite engineers likes using dBW at higher power levels. It is convenient to have these numbers next to each other so you do not have to convert when switching between disciplines.

Knowing the amount of power a signal has doesn’t necessarily tell you the voltage it swings; for that, you need impedance. That requires the impedance. If the load is purely resistive, the RMS voltage equals the square root of the power multiplied by resistance. A single watt through a fifty ohm system results in an RMS voltage of 7.071 volts. In contrast, that same watt result in 8.660 volts on a seventy-five ohm system. The converter allows you to select particular impedances such as six hundred or even fifty ohms. It will show the number in RMS, peak, or peak to peak.

The tool breaks down all of its results in four cards. The watts card includes both absolute power and the watt-equivalent in microwatts. The milliwatts card repeats those numbers in terms of milliwatts. The dBm card shows the decibel-milliwatt value along with the equivalent value in dBW below. Finally, the voltage card reports voltage at whatever impedance you’ve chosen.

Below are all of the substitutions used, broken out one per line so that you can use this as a kind of check against your own computations if you wish. And so there are preset power levels that load and never go away in wireless. Near zero dBm is transmitted by Bluetooth Low Energy. Twenty dBm is what a common Wi-Fi access point operates at. The uplink from a mobile phone peaks at about twenty-three dBm.

These receiver-side presets shows just how low the power levels are when receiving a signal. From transmitter to receiver they span over fifteen orders of magnitude. The numbers are huge: radio math is unforgiving. Milliwatts can become watts if a decimal point is misplaced; a feeble signal may dissapear below the noise floor.

This calculator covers everything from decibels all the way back to real voltage and power by using both the forward and reverse formulas. First, set the preset. Next, tweak either the load or the level. Last, read the four cards and use the breakdown as a check on your own hand calculations. Whether you’re reading a datasheet or calculating a link budget, the converter provides reliable numbers within seconds. You should of used this earlier.