dB Attenuation Calculator

About this calculator

This calculator finds signal loss in decibels using dB = 10·log₁₀(Pout/Pin), the standard power-ratio decibel formula (for voltage or amplitude ratios the multiplier becomes 20 instead of 10, since power scales with the square of voltage). A negative result means attenuation — the signal lost power passing through a cable, connector, or medium — while a positive result means gain. The logarithmic scale is used because signal power in real systems spans many orders of magnitude, which decibels compress into a manageable range.

RF and telecom engineers use this to specify cable, connector, and free-space path loss in link budgets, audio engineers use it for mixer and amplifier gain staging, and network technicians use it to verify that fiber or coax runs meet spec after installation. Anywhere a spec sheet lists loss “per 100 meters” or “per connector” in dB, this is the formula behind that number.