RF Unit Converter: dBm, dBW, Watts, Volts
Enter any RF power value in dBm, dBW, watts, milliwatts, or microwatts and instantly see all equivalent representations. Add a system impedance (50 ohm for RF, 75 ohm for cable or video) to also get the RMS voltage, peak voltage, and field-strength in dBuV. Every conversion step is shown so you can follow the math.
Why RF engineers use dBm and dBW
Radio-frequency signal levels span a huge dynamic range. A cellular base station transmitter puts out 40 watts (+46 dBm) while the minimum detectable signal at its receiver may be a tenth of a picowatt (-100 dBm). That is a ratio of 4 quadrillion to one. Expressing such a range in plain watts requires exponential notation and makes mental arithmetic nearly impossible. Decibel units solve this by using a logarithmic scale: every +10 dBm step multiplies power by 10, and every +3 dBm step (technically 3.01 dB) doubles it. System gains and losses can then be added and subtracted as simple numbers rather than multiplied and divided as ratios. dBm references the decibel to 1 milliwatt; dBW references it to 1 watt. The only difference is a constant offset: dBW = dBm - 30.
How power and voltage relate through impedance
In RF work, "power" and "voltage" are linked by the system impedance. The standard RF impedance is 50 ohm, chosen historically to balance low loss and high power-handling in coaxial cable. Broadcast and cable-television systems use 75 ohm, and some audio and telecom systems use 600 ohm. The relationship is P = V_rms^2 / Z, or equivalently V_rms = sqrt(P * Z). So 0 dBm (1 mW) across 50 ohm corresponds to about 224 mV RMS, while across 75 ohm the same power gives about 274 mV RMS. When you compare voltages between systems with different impedances, always check which impedance applies. The dBuV unit expresses voltage in decibels relative to 1 microvolt: dBuV = 20 * log10(V_rms / 1 uV).
The 3 dB and 10 dB mental math rules
Two rules let you do RF arithmetic in your head. First, adding 3 dB doubles the power (or multiplies voltage by sqrt(2) = 1.41). Subtracting 3 dB halves the power. Second, adding 10 dB multiplies power by exactly 10. Subtracting 10 dB divides it by 10. Combining these: +13 dB is roughly 20x power, +20 dB is 100x, +30 dB is 1000x. For example, a 23 dBm transmitter (200 mW) feeding a 6 dBi antenna radiates an EIRP of 29 dBm, which is just under 1 watt. Link budgets, noise-figure calculations, and cascaded-gain analysis all use these additive decibel rules to track signal through a chain of components.
Peak vs RMS voltage in RF signals
RF power measurements are always referenced to the RMS (root-mean-square) value of the waveform, not the peak. For a pure sine wave, V_peak = V_rms * sqrt(2) = V_rms * 1.414, and V_peak-to-peak = 2 * V_peak. A spectrum analyzer measures in RMS, a vector signal analyzer can show instantaneous peak values, and an oscilloscope typically shows peak-to-peak. When comparing measurements from different instruments, confirm which voltage quantity is being reported. Modulated signals such as OFDM (used in Wi-Fi and LTE) have a high peak-to-average power ratio (PAPR) that can be 10 dB or more, meaning the peak voltage is far above what simple power-to-voltage conversion suggests.
Common RF power levels
| dBm | dBW | Watts | mW | Vrms (50 ohm) | Application |
|---|---|---|---|---|---|
| -130 | -160 | 1 pW | 0.001 uW | 0.007 uV | Thermal noise floor (~1 Hz BW) |
| -113 | -143 | 5 pW | 0.005 uW | 0.016 uV | LTE receiver noise floor |
| -100 | -130 | 10 pW | 0.01 uW | 0.022 uV | Minimum detectable signal (typical) |
| -90 | -120 | 100 pW | 0.1 uW | 0.071 uV | Weak GPS receiver signal |
| -80 | -110 | 10 nW | 0.01 uW | 0.22 uV | Wi-Fi minimum sensitivity |
| -70 | -100 | 100 nW | 0.1 uW | 0.71 uV | Good receive signal (cellular) |
| -60 | -90 | 1 uW | 0.001 mW | 2.24 mV | Strong receive signal |
| -40 | -70 | 100 nW | 0.0001 W | 22.4 mV | Cable TV signal at outlet |
| -30 | -60 | 1 uW | 0.001 mW | 7.07 mV | Typical Bluetooth RX |
| -20 | -50 | 10 uW | 0.01 mW | 22.4 mV | Wi-Fi receiver input |
| 0 | -30 | 1 mW | 1 mW | 223.6 mV | Reference level (0 dBm) |
| 10 | -20 | 10 mW | 10 mW | 707 mV | Bluetooth Class 1 transmit |
| 20 | -10 | 100 mW | 100 mW | 2.24 V | Wi-Fi AP transmit power |
| 23 | -7 | 200 mW | 200 mW | 3.16 V | LTE handset max transmit |
| 27 | -3 | 500 mW | 500 mW | 5.00 V | DECT cordless phone TX |
| 30 | 0 | 1 W | 1000 mW | 7.07 V | Handheld VHF radio |
| 36 | 6 | 4 W | 4000 mW | 14.1 V | Motorola UHF portapack |
| 40 | 10 | 10 W | 10 W | 22.4 V | Small PMR base station |
| 43 | 13 | 20 W | 20 W | 31.6 V | Typical LTE small cell |
| 46 | 16 | 40 W | 40 W | 44.7 V | CDMA base station sector |
Representative signal levels used across RF systems. Values assume 50-ohm impedance for voltage columns.
Frequently asked questions
What is the difference between dBm and dBW?
Both are logarithmic power units. dBm is referenced to 1 milliwatt and dBW is referenced to 1 watt. The conversion is exact: dBW = dBm - 30, so 0 dBm equals -30 dBW, and 30 dBm equals 0 dBW (1 watt). dBm is more common in component and system level work; dBW is preferred in satellite and high-power broadcast contexts where values would otherwise be large positive dBm numbers.
How do I convert dBm to watts?
Use the formula P(W) = 10^(dBm / 10) / 1000. For example, 30 dBm: 10^(30/10) / 1000 = 1000 / 1000 = 1 watt. For negative values, 0 dBm = 10^0 / 1000 = 1/1000 = 0.001 W = 1 mW. The reverse is: dBm = 10 * log10(P_mW), where P_mW is the power in milliwatts.
Why does RF engineering use 50-ohm impedance?
The choice of 50 ohm for coaxial RF systems is a historical compromise. The impedance that minimizes attenuation in air-filled coax is about 77 ohm, while the impedance for maximum power handling is about 30 ohm. An average of those is around 50 ohm, which was standardized during World War II and has remained the worldwide RF standard. Cable television uses 75 ohm because it matches the characteristic impedance of a dipole antenna and minimizes signal loss in long distribution runs.
What is 0 dBm in volts?
0 dBm is 1 milliwatt. Into 50 ohm: V_rms = sqrt(0.001 W * 50 ohm) = sqrt(0.05) = 0.2236 V, or about 224 mV RMS. The peak voltage is 224 * 1.414 = 316 mV and the peak-to-peak is 632 mV. Into 75 ohm the same 1 mW gives V_rms = sqrt(0.001 * 75) = 274 mV.
How do I add two power levels in dBm?
You cannot add dBm values directly because they are logarithmic. Convert both to milliwatts, add them, then convert back. For example, 10 dBm + 10 dBm is not 20 dBm: 10 dBm = 10 mW, so two such signals add to 20 mW = 13 dBm (an increase of 3 dB, not 10). However, you can add decibel gains and losses along a signal chain because those represent multiplication ratios, not absolute power levels.
What does dBuV mean in RF measurements?
dBuV (decibels relative to 1 microvolt) is used to express voltage levels in RF, especially in EMC (electromagnetic compatibility) measurements and broadcast receiver specifications. The formula is dBuV = 20 * log10(V_uV), where V_uV is the voltage in microvolts. To convert to dBm across 50 ohm, use: dBm = dBuV - 107 (at 50 ohm). At 75 ohm the offset is dBm = dBuV - 108.75.
What is a typical receiver sensitivity in dBm?
Receiver sensitivity varies by technology. A GPS receiver needs at least -130 dBm. Wi-Fi 802.11ac requires approximately -82 dBm at the highest data rate. LTE handsets are typically specified to work down to about -97 dBm. A handheld VHF radio may need -116 dBm for 12 dB SINAD. Sensitivity depends on the noise figure, bandwidth, and required signal-to-noise ratio for the modulation scheme.