ForHosting KIT · Engineering & construction

Smoothing capacitor calculator

A 1 A load on 50 Hz mains with 1 V of ripple needs 10 000 µF after a full-wave rectifier, because the ripple runs at 100 Hz. Enter the load current, the ripple you can accept and the line frequency to size the filter capacitor. Free in your browser.

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Run — free How it works & API

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Worked example

If you enter

Load current: 1
Ripple voltage: 1
Mains: 50

You get

Rectifier: Full F
N: 2
Capacitance f: 0.01
Capacitance uf: 10,000

This smoothing capacitor calculator sizes the filter capacitor after a rectifier when you know the DC load current, the peak-to-peak ripple voltage you can tolerate, and the AC mains frequency. The standard capacitor-input approximation is C equals I divided by n times f times Vr, where n is two for full-wave rectification (ripple at twice the line frequency) and one for half-wave. When current is in amperes, frequency in hertz, and ripple in volts, capacitance is returned in farads and also in microfarads for common electrolytic selection. Zero or negative ripple is rejected because the formula would require infinite capacitance; zero or non-positive load current and frequency are rejected for the same physical reason. The engine is fully deterministic arithmetic: no network calls, no sampling, and no date-dependent shortcuts.

What a smoothing capacitor does and what you get

After a half-wave or full-wave rectifier, the raw DC still contains a large AC component at the line frequency or at twice the line frequency. A reservoir (smoothing) capacitor across the load charges near each peak and discharges into the load between peaks, reducing the peak-to-peak ripple voltage Vr seen by the rest of the circuit.

Under the usual first-order model that treats the discharge as roughly linear for small ripple relative to the average DC, the charge removed per cycle is approximately I times the period of the ripple waveform, so C times Vr is about I over n f, which rearranges to C equals I divided by n times f times Vr. Here I is the DC load current, f is the mains frequency, and n is two for full-wave (default) or one for half-wave.

Zero ripple is called out explicitly because it would demand infinite filter capacitance.

Where filter capacitance sizing fits in study, design, and software

Students meet C equals I over two f Vr when a textbook introduces capacitor-input filters, when a homework problem gives a one-amp load at fifty hertz with one volt of ripple and asks for farads or microfarads, or when a lab asks why full-wave supplies need roughly half the capacitance of half-wave designs for the same ripple budget. Teachers can pre-generate answer keys for modest currents and ripple targets without trusting opaque calculator apps that silently switch units or confuse RMS ripple with peak-to-peak.

Developers call the same contract from scripts to seed deterministic test vectors for power-supply demos, to normalize user-entered filter parameters before a design checklist, or to satisfy programming-challenge statements that demand farads rather than a hand-waved sketch. First-order electrical checks use this formula when only load current, a ripple budget, and line frequency are known before ESR, hold-up time, or multi-stage LC filters are modeled.

What you can do with it

Homework and lab checks

Compute C = I/(n·f·Vr) from load current, ripple budget, and mains frequency before grading worksheets or comparing filter sizes.

Tutoring and teaching software

Normalize user-entered I, Vr, and f into required filter capacitance for interactive lessons and step helpers.

FAQ

What does the smoothing capacitor calculator cost?

It is free in your browser on this page.

What formula is used for the filter capacitance?

The standard capacitor-input approximation is C = I / (n · f · Vr), where I is load current, f is mains frequency, Vr is peak-to-peak ripple, and n is 2 for full-wave (default) or 1 for half-wave. With SI inputs the unit is farads (F); the response also reports microfarads.

What happens if ripple voltage is zero?

Zero ripple would require infinite filter capacitance in this model; choose a positive peak-to-peak ripple budget.

Full-wave or half-wave — which should I use?

For the same I, f, and Vr, half-wave needs twice the capacitance of full-wave.

Is this the same as capacitor stored energy E = ½CV²?

No. Capacitor energy answers how many joules are stored at a given C and V. This tool sizes the reservoir capacitor needed to meet a ripple budget under load. Use the capacitor energy calculator when you need joules from C and V.

Related tools

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/elec/smoothing-capacitor

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/elec/smoothing-capacitor \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"load_current":1,"ripple_voltage":1,"frequency":50}'

const res = await fetch("https://api.kit.forhosting.com/elec/smoothing-capacitor", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "load_current": 1,
    "ripple_voltage": 1,
    "frequency": 50
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/elec/smoothing-capacitor",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "load_current": 1,
    "ripple_voltage": 1,
    "frequency": 50
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/smoothing-capacitor", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"load_current":1,"ripple_voltage":1,"frequency":50}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"load_current":1,"ripple_voltage":1,"frequency":50}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/smoothing-capacitor", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "load_current": 1,
  "ripple_voltage": 1,
  "frequency": 50
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "elec.smoothing_capacitor",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

`max_abs_current`	1000000000000000
`max_abs_ripple`	1000000000000000
`max_abs_frequency`	1000000000000000

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Technical notes

What a smoothing capacitor does and what the response contains

This calculator returns the normalized inputs load_current, ripple_voltage, and frequency, the resolved rectifier kind and multiplier n, the computed capacitance in farads and microfarads, the ripple frequency n f, the precision used, a method tag smoothing_capacitor, a short formula reminder, and a unit hint F for SI inputs. There is no numerical SPICE simulation, no ESR or ripple-current derating, and no Monte Carlo sampling: the engine either evaluates I over n f Vr inside the supported numeric range or rejects the input with invalid_input. Rejected cases include a missing load current, ripple voltage, or frequency; non-finite values; magnitudes above the documented ceilings; and any non-positive I, f, or Vr.

How load current, ripple, and frequency are read and how C stays reproducible

Ripple must be a finite positive peak-to-peak allowance; zero ripple is rejected because C equals I over n f Vr diverges as Vr approaches zero, and negative ripple is not physical in this model. Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces and non-numeric tokens are rejected. The preferred field for load current is load_current, but aliases I, i, current, amps, and load are accepted so spreadsheets, query strings, and typed forms can reuse the same contract. Load current must be finite and strictly positive: zero or negative I fails with invalid_input and a message that names the field, so a bad cell does not become a silent nonsense result. The preferred field for ripple is ripple_voltage, with aliases Vr, vr, ripple, delta_v, and Vripple. The preferred field for frequency is frequency, with aliases f, freq, mains_frequency, hz, and line_frequency; typical values are fifty or sixty hertz for mains-powered equipment, but any positive finite f is accepted within the magnitude ceiling. Optional rectifier, with aliases type, wave, and rectification, selects full-wave (n equals two, default) or half-wave (n equals one); synonyms such as full-wave, half-wave, fw, and hw are accepted case-insensitively. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose for the numeric outputs, defaulting to ten and capped at fifteen so JSON goldens stay stable. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing the smoothing capacitor formula yourself.

Where filter capacitance sizing fits in study, design, and software

Education tools use the endpoint when a learner types I, Vr, and f and the UI must show capacitance in farads and microfarads. On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result. Pair it with capacitor energy or electrical power helpers when you need related circuit quantities, and with other math endpoints when you are building a small lab of free, deterministic electronics calculators.

Integration use cases

Deterministic test fixtures

Generate reproducible smoothing capacitance values for unit tests, PSU demos, and CI assertions on the reservoir formula.

Read the full KIT documentation →

Run — free

Worked example

What a smoothing capacitor does and what you get

Where filter capacitance sizing fits in study, design, and software

What you can do with it

Homework and lab checks

Tutoring and teaching software

FAQ

Related tools

For developers — API access

API endpoint

Call it from your stack

Example request

Example response

Pricing

Limits

Errors

Technical notes

What a smoothing capacitor does and what the response contains

How load current, ripple, and frequency are read and how C stays reproducible

Where filter capacitance sizing fits in study, design, and software

Integration use cases

Deterministic test fixtures

thank you