About

Decibel-milliwatts (dBm) express absolute power using a logarithmic scale referenced to 1mW. This notation compresses the enormous dynamic range found in RF systems - from femtowatt receiver sensitivities to kilowatt transmitters - into manageable two-digit numbers. The conversion formula P_W = 10^(dBm/10) × 10⁻³ is nonlinear, meaning mental arithmetic fails quickly: +3dBm doubles power, but +10dBm multiplies it by ten. Misreading a link budget by 3dB can halve your effective range or violate regulatory emission limits.

This calculator performs bidirectional conversion with automatic unit scaling down to nanowatts. Input values are validated against physical constraints - negative wattage is meaningless, and 0W corresponds to −∞dBm. Use it for antenna system design, amplifier specifications, or verifying test equipment readings. Note: calculations assume ideal conditions without cable loss or impedance mismatch.

Formulas

The decibel-milliwatt scale is logarithmic, compressing multiplicative power ratios into additive decibel steps. The fundamental conversion equations derive from the definition of dBm as ten times the base-10 logarithm of power in milliwatts.

P_W = 10^dBm101000

where P_W is power in watts and dBm is the decibel-milliwatt value. The inverse conversion from watts to dBm applies the logarithm.

dBm = 10 × log₁₀(P_W × 1000)

where P_W > 0. Key relationships: +3dB doubles power, +10dB multiplies by 10, and 0dBm = 1mW by definition. The division by 1000 converts milliwatts to watts.

Reference Data

dBm	Watts	Milliwatts	Typical Application
+60	1000W	1,000,000mW	Commercial broadcast transmitter
+50	100W	100,000mW	Amateur radio HF station
+40	10W	10,000mW	Portable VHF/UHF radio
+37	5W	5,000mW	Maximum WiFi AP (some regions)
+33	2W	2,000mW	GSM mobile phone peak
+30	1W	1,000mW	Typical WiFi router maximum
+27	0.5W	500mW	LTE UE max power (Class 3)
+23	0.2W	200mW	Bluetooth Class 1
+20	0.1W	100mW	WiFi client device typical
+17	0.05W	50mW	LoRa module maximum
+10	0.01W	10mW	Low-power ISM devices
+4	0.0025W	2.5mW	Bluetooth Class 2
0	0.001W	1mW	Reference level (0 dBm = 1 mW)
−3	0.0005W	0.5mW	Bluetooth Class 3
−10	0.0001W	0.1mW	Typical received WiFi signal
−20	10μW	0.01mW	Strong cellular signal
−30	1μW	0.001mW	Good WiFi reception
−50	10nW	0.00001mW	Marginal WiFi signal
−70	100pW	10⁻⁷mW	Weak cellular signal
−80	10pW	10⁻⁸mW	Minimum usable WiFi
−90	1pW	10⁻⁹mW	GPS receiver sensitivity
−100	100fW	10⁻¹⁰mW	Cellular receiver threshold
−110	10fW	10⁻¹¹mW	Thermal noise floor (10 MHz BW)
−120	1fW	10⁻¹²mW	Radio astronomy receiver
−174	4×10⁻¹⁸mW	-	Thermal noise floor (1 Hz BW at 290K)

Frequently Asked Questions

The dBm scale uses a logarithm, and log₁₀(0) is mathematically undefined - it approaches negative infinity. In practical terms, 0W means no signal exists, which corresponds to infinitely negative dBm. Real measurement equipment typically bottoms out around −120 to −174 dBm due to thermal noise floors.

Both are absolute power units. dBm references 1 milliwatt while dBW references 1 watt. Since 1W = 1000mW, the conversion is simply dBW = dBm − 30. For example, +30 dBm equals 0 dBW (both represent 1 watt).

A +3 dB increase doubles the power; −3 dB halves it. This comes from 10^(3/10) ≈ 2. This relationship is critical in link budgets: adding a 3 dB attenuator cuts your transmitted power in half, potentially halving your communication range in free-space conditions.

No. Audio typically uses dBu (referenced to 0.775V), dBV (referenced to 1V), or dB SPL (sound pressure). These are voltage or pressure ratios, not power. The dBm scale specifically measures electrical power referenced to 1mW into a defined impedance (historically 600Ω for telecom, 50Ω for RF).

Logarithmic scales compress huge dynamic ranges into manageable numbers. A receiver might detect −110 dBm (10 femtowatts) while a transmitter outputs +50 dBm (100 watts) - a ratio of 10^16. Additionally, gains and losses in dB simply add: a +20 dBm signal through a −6 dB cable yields +14 dBm at the output.

None. dBm is purely a power unit, independent of impedance. However, when measuring voltage across a known impedance R, power P = V²/R. A 50Ω system at 0 dBm shows 224 mV RMS; a 75Ω system shows 274 mV RMS for the same 1mW power.