NewLife✨

📻 Modulation Index Calculator

Calculate the modulation index for amplitude modulation (AM) or frequency modulation (FM) signals.

Modulation Type

AM: Message Amplitude / FM: Frequency Deviation

V or Hz

AM: Carrier Amplitude / FM: Modulating Frequency

V or Hz

What modulation index means

The modulation index describes how strongly a carrier signal is modulated by an information (message) signal. Different values are used for amplitude modulation (AM) and frequency modulation (FM).

The formulas

For AM, modulation index m = E_m / E_c, where E_m is the peak amplitude of the message signal and E_c is the peak amplitude of the carrier. A value of m=1 corresponds to 100% modulation. For FM, modulation index β = Δf / f_m, where Δf is the peak frequency deviation and f_m is the modulating (message) signal frequency.

These are the standard formulas used in analog communications engineering for describing AM and FM signal modulation depth.

Last reviewed August 2026