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dB to Watt Converter

Convert dBm or dBW to 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

Decibels (dBm)

dBm

−1200+60

Current value: +20 dBm (slider −120 to +60; type for wider range)

Common RF Power Levels

Result

Absolute Power

—

power (auto-scaled)

—

Watts

—

Milliwatts

—

Equivalent (other mode)

—

V_rms across 50 Ω

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Formulas

dBm → power: P(mW) = 10^(dBm / 10) ; P(W) = 10^((dBm − 30) / 10)

dBW → power: P(W) = 10^(dBW / 10) ; P(mW) = 10^((dBW + 30) / 10)

Mode bridge: dBm = dBW + 30 (1 W = 1000 mW → +30 dB)

Voltage across 50 Ω: V_rms = √(P × 50) — RF reference impedance

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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 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).

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.

Why these specific reference values?

1 mW (0 dBm) emerged historically as a convenient telecom reference — early phone audio levels and microwave test gear 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 prefer dBm because typical signal powers span many orders below 1 W; broadcast and radar prefer dBW because typical transmit powers are above 1 W.

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 floors sit around −95 to −100 dBm for WiFi.

Frequently Asked Questions

What is +30 dBm in watts?

+30 dBm = 10^(30/10) = 10³ = 1000 mW = 1 W. This is the standard regulatory cap for WiFi 2.4 GHz routers in the US (effective isotropic radiated power, EIRP). Each +10 dBm = 10× the power, so +20 dBm = 100 mW, +40 dBm = 10 W, and so on.

How do I convert dBm to dBW (or vice versa)?

Subtract or add 30: 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.

Why does my WiFi receive signal look like −80 dBm — that's a tiny number, right?

Yes — −80 dBm is 10 picowatts (10⁻¹¹ watts). Modern radios are astonishingly sensitive. WiFi typically works down to about −90 dBm (1 pW), and below −95 dBm the link usually breaks. Cellular UEs can decode at −110 dBm (10 fW) thanks to processing gain and forward error correction.

Is +6 dBm "double" of +3 dBm?

No. +3 dB = double power, so +6 dBm = 4× the power of +3 dBm. Specifically: +3 dBm = 1.995 mW, +6 dBm = 3.98 mW, +10 dBm = 10 mW. The doubling rule for amplitude (×2 = +6 dB) is different from the doubling rule for power (×2 = +3 dB). Since dBm and dBW are power units, +3 dB always means "double power" here.

What's "EIRP" and how is it different from transmit power?

EIRP = Effective Isotropic Radiated Power. It's the transmit power that an ideal omnidirectional (isotropic) antenna would need to produce the same signal in your antenna's main beam direction. EIRP = TX power + antenna gain (dB). A 100 mW (+20 dBm) router into a 6 dBi gain antenna has +26 dBm EIRP ≈ 400 mW in the direction the antenna favors. Regulatory limits (FCC, ETSI) are usually specified as EIRP, not raw TX power.

What does "−174 dBm/Hz" mean?

It's the thermal noise spectral density at 290 K — the noise power per 1 Hz of bandwidth. To get noise in a wider bandwidth, add 10·log₁₀(BW): for a 1 MHz channel, noise ≈ −174 + 60 = −114 dBm. For 20 MHz WiFi, ≈ −101 dBm. Real receivers add a "noise figure" (NF) of typically 3 to 10 dB on top. Below this floor, no signal can be reliably extracted.

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