Capacitor Size Calculator
Enter the load current, the ripple voltage you can accept, the peak voltage, the mains frequency and the rectifier type. The calculator gives the capacitance needed, the nearest standard value, the voltage rating and the ripple current.
- Smoothing capacitance
- Voltage rating
- Ripple current
Peak voltage is the transformer's RMS voltage × 1.414, minus about 1.4 V for a bridge rectifier.
Bigger load or less ripple means a bigger capacitor. For a full-wave rectifier, C = I ÷ (2 × f × V ripple). A 1 A load on 50 Hz mains with 1 V of ripple needs 10,000 µF. Half-wave rectifiers need twice as much.
Capacitor size chart
Full-wave, 50 Hz, 1 V ripple. Search for a current.
| Load (A) | Needed (µF) | Standard (µF) |
|---|---|---|
| 0.1 | 1000 | 1000 |
| 0.25 | 2500 | 3300 |
| 0.5 | 5000 | 6800 |
| 1 | 10000 | 10000 |
| 2 | 20000 | 22000 |
| 3 | 30000 | 33000 |
| 5 | 50000 | 68000 |
Rounded up to standard values.
Load current
Full-wave, 50 Hz, 1 V ripple. Slide the current.
The waveform shows the rectified mains and the smoothed output with its ripple.
How to size a smoothing capacitor
Current to µF. Step through it.
Load current
Maximum.
A voltage regulator after the capacitor needs its dropout voltage above the lowest point of the ripple.
Half-wave, full-wave or bridge
Rectifiers. Compare them.
One diode.
Two diodes.
Four diodes.
Full-wave ripple is twice the mains frequency, so the capacitor can be half the size.
Before you build
Supply checks. Tick each item.
Tick each item as you go.
Large capacitors draw a big inrush current at switch-on, so check the fuse and diodes can take it.
What you get
Capacitor sizing. Each tile explains one result.
µF.
Value.
Rating.
Current.
Min and average.
Electrolytic capacitors are polarised. Fitting one backwards can make it burst.
Frequently Asked Questions
No question matches that search.
How do I calculate a smoothing capacitor?
Divide the load current by twice the mains frequency times the ripple voltage for full-wave rectifiers.
What voltage rating should the capacitor have?
At least a quarter more than the peak voltage.
How much ripple is acceptable?
Often about five to ten per cent of the DC voltage before a regulator.
Why does full-wave need a smaller capacitor?
The capacitor is topped up twice as often, so it discharges less between peaks.
What is ripple current?
The AC current that flows in and out of the capacitor, which heats it.
Can I use a bigger capacitor?
Yes. Ripple falls, but switch-on current rises.
What does µF mean?
Microfarads, millionths of a farad.
Smooth, steady DC
Size the capacitor for your current and ripple, with a safe voltage and ripple rating, and the supply runs cool and quiet.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.