decibelWatts

Decibel-watts (dBW) is a logarithmic unit used to express power relative to one watt. It is defined as P(dBW) = 10 log10 [P(W) / 1 W], where P(W) is the power in watts. Equivalently, P(W) = 10^[P(dBW)/10] watts. The decibel is a dimensionless unit; dBW expresses a power magnitude as a decibel ratio with 1 W as the reference.

Decibel-watts are commonly used in radio frequency engineering and telecommunications to specify transmitter output power, receive sensitivity, link budgets, and RF system performance. Because the reference is 1 W, 0 dBW equals 1 W, 10 dBW equals 10 W, 20 dBW equals 100 W, and so on. Negative values indicate powers below 1 W (e.g., -10 dBW ≈ 0.1 W).

Decibel-watts are related to decibel-milliwatts (dBm) by the simple relation: dBm = dBW + 30. Conversely, dBW = dBm − 30. In practice, dBW is preferred when the reference is large (watts to kilowatts), and dBm when working with milliwatts. Because dBW expresses a power, converting to a voltage or current requires knowledge of the system impedance: P = V^2 / R or P = I^2 R.

Although the term decibel-watts is common in RF contexts, many instruments report power in dBW or dBm, and care should be taken to use the correct reference.