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RMS Voltage Calculator

An online calculator can convert other measures of AC voltage into RMS.


Volts (V)


Volts (V)

How do you calculate RMS Voltage?

RMS voltage stands for root mean square voltage. It is a measure of direct rather than alternating current. Direct current is easy to measure. A simple voltmeter is enough for me to measure direct current. Simply hooking a voltmeter up to a wire is enough to measure it. Direct current is continuously changing, and therefore, I cannot measure it in this way.

Sometimes, it is possible to measure alternating current with peak voltage or with peak-to-peak voltage. Peak voltage measures the highest voltage that the AC reaches during its cycle. Peak to peak voltage measures the difference between the highest and the lowest level of voltage reached.

The strength of an alternating current constantly changes, so it is not as simple to measure the current. I have to take the lower and higher points into consideration.

The most common way to measure alternating current is to use the RMS (root mean square). The mean voltage, or RMS voltage, is the best measure of the strength of the current in an AC circuit.

The best way to estimate the RMS voltage is to take the peak voltage and multiply it by 0.707. Since the RMS voltage follows something similar to a sine wave pattern, the RMS voltage is likely to be about 0.707 times the peak voltage.

Calculating the RMS voltage more accurately is a bit more difficult. One must take many samples of the voltage in an alternating current, with very little time between each measurement.

For the current in an alternating circuit to go from its high point to its low point and from there back to its high point takes only 1/60th of a second. One must, therefore, take measurements that are much faster than 1/60th of a second to measure RMS in this way.

If one takes measurements 1200 times per second, they can end up with 20 measurements for a single cycle. From there, some math is required to calculate the RMV.

One must first find the square of all 20 (or ideally as many as possible) values, and then add all of these numbers together. One then finds the square root of the final number, and that is the RMV voltage.

What is the RMS Value?

The actual RMS Value can only be determined by taking a lot of small measurements of each cycle and using math to calculate the RMV. Only a high-quality voltmeter can calculate the RMS by actually taking a lot of small measurements and determining the result.

A cheaper voltmeter will only multiply the peak voltage by 0.707 to estimate the RMS. Some AC circuits do not follow a sine wave pattern. For this reason, a cheaper voltmeter may give very inaccurate results for some AC circuits. One should be aware of the limitations of the tools they use. A more advanced voltmeter is required to get accurate RMS values for some circuits.

What is an RMS calculator for?

If a simple estimate of RMS is good enough, one does not need an expensive voltmeter that can truly measure RMS. These online tools are for converting peak voltage to RMS, peak-to-peak voltage to RMS, or average voltage to RMS.

Damon Coleman

Entrepreneur, robotics fan. I have a Diploma in Technical Education, interested in robotics. My favorite platforms are Arduino and Raspberry Pi. Welcome to the world of robotics!

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