dB to Watt Converter
This dB to watt converter turns dBm or dBW into absolute power. Uses P = 10^(dBm/10) mW or P = 10^(dBW/10) W, with auto-scaling to femtowatts through megawatts and zone labels from broadcast transmit down to the thermal noise floor.
Input
Result
Common dBm / dBW Reference
| dBm | dBW | Power | Real-World Example |
|---|---|---|---|
| +90 dBm | +60 dBW | 1 MW | AM radio broadcast transmitter |
| +80 dBm | +50 dBW | 100 kW | FM radio / TV transmitter |
| +60 dBm | +30 dBW | 1 kW | High-power amateur radio |
| +50 dBm | +20 dBW | 100 W | Typical HF amateur amplifier |
| +40 dBm | +10 dBW | 10 W | VHF/UHF mobile rig; many EIRP caps |
| +36 dBm | +6 dBW | 4 W | Cellular UE peak transmit |
| +30 dBm | 0 dBW | 1 W | WiFi router max (US 2.4 GHz EIRP) |
| +23 dBm | −7 dBW | ~200 mW | WiFi laptop / phone TX peak |
| +20 dBm | −10 dBW | 100 mW | Typical WiFi transmit |
| +10 dBm | −20 dBW | 10 mW | Bluetooth Class 1 max |
| +4 dBm | −26 dBW | ~2.5 mW | Bluetooth Class 2 max |
| 0 dBm | −30 dBW | 1 mW | Reference (laser pointer, BLE) |
| −30 dBm | −60 dBW | 1 µW | Strong WiFi receive signal |
| −60 dBm | −90 dBW | 1 nW | Solid WiFi signal a few rooms away |
| −80 dBm | −110 dBW | 10 pW | Workable WiFi signal |
| −100 dBm | −130 dBW | 0.1 pW | Cellular at edge of service |
| −120 dBm | −150 dBW | 1 fW | Sensitive receiver threshold |
| −174 dBm/Hz | −204 dBW/Hz | ~4 × 10⁻²¹ W/Hz | Thermal noise floor at 290 K |
About dBm, dBW & Absolute Power
dBm and dBW are absolute power units — unlike a plain "dB" which is a dimensionless ratio, these specify what 0 dB refers to. 0 dBm = 1 milliwatt, and 0 dBW = 1 watt. Because 1 W = 1000 mW = 30 dB above 1 mW, the two scales are offset by exactly 30: dBm = dBW + 30. Both convert to linear power with the ÷10 form: P = 10^(dB / 10), since dBm and dBW measure power directly (not amplitude). This RF power calculator handles both modes and auto-scales the result from femtowatts to megawatts, making it useful whether you are sizing antenna power budgets or tracing a received WiFi power level back to milliwatts. To go the other direction — convert measured watts or milliwatts back — use the Watt to dB Converter.
Why ÷10 and not ÷20?
The ÷20 form is for amplitude (voltage, sound pressure, field strength). The ÷10 form is for power (watts, intensity, energy flux). Since dBm and dBW are power units, we use ÷10. If you have a voltage in dBV and want power, you have to know the load impedance — a 1 V signal across 50 Ω is 20 mW (+13 dBm), but across 600 Ω it's 1.67 mW (+2.2 dBm). dBm sidesteps that ambiguity by always referring to power directly. For amplitude-ratio dB conversions (dBV, dBFS, dBu), see the dB to Amplitude Converter.
Why these specific reference values?
1 mW (0 dBm) emerged historically as a convenient telecom reference — early telephone audio levels and microwave test equipment were normalized around 1 mW into 600 Ω (audio) or 50 Ω (RF). 1 W (0 dBW) is the natural SI choice. Telecom and RF engineering prefer dBm because typical received signal powers span many orders of magnitude below 1 W; broadcast and radar applications prefer dBW because typical transmit powers run above 1 W. In link budget calculations, gains (amplifiers, antenna directivity) are added and losses (cable attenuation, free-space path loss, connector insertion loss) are subtracted — all as simple arithmetic on the dB scale.
The thermal noise floor: −174 dBm/Hz
Every receiver competes with thermal noise at kTB — Boltzmann's constant × temperature × bandwidth. At room temperature (290 K), this is −174 dBm per Hz of bandwidth. For a 20 MHz WiFi channel that's −174 + 10·log₁₀(20×10⁶) ≈ −101 dBm — the absolute floor below which no signal can be reliably detected. Real receivers add noise figure (NF) of a few dB on top, so practical sensitivity floors sit around −95 to −100 dBm for WiFi and −110 to −120 dBm for narrowband cellular receivers. Signal-to-noise ratio (SNR) is the difference in dB between the received signal power and this noise floor — the higher the SNR, the more robustly the link decodes.
Worked example: convert +36 dBm to watts
The formula is P(mW) = 10^(dBm / 10). To convert +36 dBm to watts, apply it step by step: divide the dBm value by 10 to get the exponent (36 / 10 = 3.6), then raise 10 to that power (10^3.6 = 3981 mW), then divide by 1000 to get watts: ≈ 3.98 W. This is the standard peak transmit power of a cellular handset (3GPP Power Class 3, +36 dBm). Two common anchor references make mental arithmetic easier: +30 dBm = 1 W exactly (since 10^3 = 1000 mW), and +40 dBm = 10 W (since 10^4 = 10,000 mW). Every +10 dBm step multiplies power by 10; every +3 dBm step roughly doubles it. To reverse the calculation and convert a known wattage back to dBm, use the Watt to dB Converter. For amplitude-domain dB work (voltage, dBV, dBFS), see the dB to Amplitude Converter instead.
Frequently Asked Questions
What is +30 dBm in watts?
How do I convert dBm to dBW (or vice versa)?
dBW = dBm − 30 and dBm = dBW + 30. So 0 dBm = −30 dBW and 0 dBW = +30 dBm. The 30 comes from 10·log₁₀(1000), since 1 W = 1000 mW. No multiplication needed — the dB scale handles the conversion as simple addition.