What is the Difference Between dB and dBm?

The main difference between dB and dBm lies in their units and what they measure.

• dB (Decibel):
• It is a logarithmic unit of measurement used to express the ratio or difference between two power levels.
• It is a relative measurement and does not have an absolute value.
• In the context of fiber optics, dB represents the difference between two dBm values.
• dBm (Decibel Milliwatt):
• It is a unit used to express the absolute power level.
• It is an absolute unit that can be converted into watts.
• In fiber optics, dBm measurements are used to measure absolute power (e.g., signal strength or power level).
• 0 dBm is defined as 1 milliwatt (mW) of power into a power meter.

In summary:

• dB quantifies the ratio between two values (relative measurement).
• dBm expresses the absolute power level (absolute unit).
• dB is a dimensionless unit, while dBm is always relative to 1 milliwatt.
• dBm values can be converted into watts, but dB values cannot be.

Comparative Table: dB vs dBm

The difference between dB and dBm can be summarized in the following table:

dB is a dimensionless unit that quantifies the ratio between two values, while dBm is an absolute unit that expresses the power level relative to 1 milliwatt (mW). dBc is used for various purposes, including power measurements in the laboratory or field, while dBm is often used to determine cell phone signal strength at a site. A strong cell phone signal is around -70 dBm or higher, while a weak signal is around -100 dBm or lower.