# RMS

CEFR C2 · Noun

Source: https://englishreference.com/word/rms
Updated: 2026-05-09

## Definition

Stands for Root Mean Square. A way to calculate the average value of a set of numbers that change over time, like an electrical signal or sound wave. It helps you understand the true power or strength of the signal.

For teachers: Abbreviation for Root Mean Square. A statistical measure of the magnitude of a varying quantity, calculated as the square root of the arithmetic mean of the squares of the values. It is the standard method for expressing the effective value of alternating current or audio signals.

## Examples

- The speakers have an RMS power rating of 50 watts.
- Engineers use the RMS value to determine the effective voltage of an AC power supply, as it represents the equivalent DC power.
- When comparing audio amplifiers, the RMS power output provides a more accurate representation of sustained performance than the peak power rating, which only measures short bursts of energy.

## Usage notes

- Often used as a modifier before another noun (e.g., 'RMS voltage', 'RMS power').

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