What’s the Difference Between RMS and Average Current?

RMS (Root Mean Square) current and Average current are two different ways of representing the current in an alternating current (AC) circuit. They they convey different information about the current waveform:

RMS Current (I_RMS):

RMS current is a measure of the effective or equivalent current in an AC circuit.

It is used to calculate the heating effect or power dissipation in resistive components in an AC circuit, and it ensures that this calculation is equivalent to that in a direct current (DC) circuit.

I_RMS represents the magnitude of the AC current as if it were a steady DC current that would produce the same heating effect.

It is calculated using either of the following formulas:

• I_RMS = I_PEAK / √2 where I_PEAK is the peak current. ⚙ Calculator
• I_RMS = √(P_avg/R) where P_avg is the average power and R is the resistance. ⚙ Calculator
• I_RMS = √(1/n)(I₁² +I₂² + … + I_n²). ⚙ Calculator

RMS current is used for calculating power, voltage, and resistance in AC circuits.

Average Current (Iavg):

Average current, as the name suggests, represents the average value of the AC current waveform over one or more complete cycle.

It is calculated by integrating the current waveform over a complete cycle and dividing by the cycle time.

I_avg = (1/n)(I₁ +I₂ + … + I_n)

Average Current Calculator

It does not take into account the direction or the instantaneous variations of the current; it only considers the magnitude. For this reason it has limited practical value.

Measuring RMS and Average Current

Digital Multimeters can be used to measure current. However you have to read the specs and fine print carefully to see if it is capable of RMS measurements.

A true RMS multimeter like the one shown below will provide accurate current readings for any waveform type (sine, square, triangle, etc.)

Any other multimeter with current capability will only provide average measurements. The measured values are accurate for sine waves but inaccurate for every other waveform type [1].

Typically RMS multimeters are more expensive than those with average measurement capability.

Summary

⭐ Average current is not the same as RMS current.

The main difference between RMS current and average current lies in what they represent:

• RMS current represents the effective or equivalent current with respect to power calculations and is used when analyzing the heating effect or power dissipation in AC circuits.
• Average current represents the average magnitude of the current waveform and is used when you need to find the mean value of the current over time, regardless of its direction.

Both RMS and average current have their uses in AC circuit analysis.

References

[1] What is True RMS – Fluke

Related Calculators

• Average Voltage
• RMS Voltage