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RMS, or Root Mean Square, is a unit of measurement that is used to describe the continuous power handling capability of an electrical device. When it comes to audio equipment, it’s common to see RMS power listed to give an idea of how much power a speaker or amplifier can handle on a continuous basis.

If you have a 400 Watt RMS amplifier, this is the same as saying it can output 400 Watts of continuous power without damage. The term “RMS” here is used to help distinguish this from the peak power that a device may be able to handle for short bursts of time.

So, in short, 400 RMS is equal to 400 Watts, as the RMS value and the Wattage are one and the same thing in this case. The RMS is just a clarification that this is a sustained power handling ability, and not a peak power