In an AC circuit the current continuously oscillates in both magnitude and direction. For analysis we consider the root‑mean‑square (RMS) current, which reflects the overall heating effect of the waveform while ignoring its polarity. A constant DC current equal to the RMS value will dissipate the same power in a resistor as the alternating current.

Step 1 – Identify the Peak Current

Locate the maximum value of the sinusoidal current waveform (the crest). This is the peak current, often denoted I_max or I_peak.

Step 2 – Square the Peak Current

Compute I_max². For example, if I_max = 1.5 A, then 1.5² = 2.25.

Step 3 – Divide by Two

Divide the squared value by 2. Using the example: 2.25 ÷ 2 = 1.125.

Step 4 – Take the Square Root

Find the square root of the result: √1.125 ≈ 1.06 A. This value is the RMS current, I_RMS.

The calculated I_RMS is used for power calculations, safety limits, and component sizing.