Ripple Voltage
Smoothing ripple
Compute ripple from capacitance, or size the capacitor for an allowed ripple.
Result
How to use this calculator
Between charging peaks the smoothing capacitor discharges through the load, and the resulting droop is the ripple. The exact droop is ΔV = I·(1 − e^(−T/RC)) with T = 1/f (f = 100/120 Hz for full-wave, 50/60 Hz for half-wave). In **Ripple →** mode enter the capacitance to get the ripple; in **Size capacitor →** mode enter the allowed ripple and DC voltage to get the required capacitance.
What it means in a real circuit
Full-wave ripple is at twice the mains frequency, so it's easier to filter (a smaller capacitor gives the same droop). For 100 mA load, 120 Hz full-wave and a 1000 µF capacitor the ripple is ≈ 0.16 V (1.3%) — very smooth. The linear approximation I/(f·C) is shown for comparison; it slightly overestimates ripple at small RC. Real designs add margin for capacitor ESR, aging and temperature, so a practical rule is to specify at least 2× the calculated value. Use this to check an existing supply or to pick a capacitor for a new one.