Capacitive reactance calculator
A 100 µF capacitor at 60 Hz presents about 26.5258238486 Ω, and the figure drops as frequency or capacitance rises. Enter the frequency in hertz and the capacitance in farads to get the reactance and the angular frequency. Free in your browser.
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- No sign-up
- Your data stays on your device
Run — free
Worked example
- Signal frequency in hertz
- 60
- Capacitance in farads
- 0.0001
- Reactance
- 26.5258238486 ohm
- Capacitive reactance
- 26.5258238486
- Xc
- 26.5258238486
- Ohms
- 26.5258238486
Capacitive reactance is the frequency-dependent opposition a capacitor presents to alternating current, measured in ohms and written Xc equals one over two pi f C when frequency is in hertz and capacitance is in farads. Unlike resistance, it falls as frequency or capacitance rises, so a large electrolytic looks nearly like a short at high frequency while a tiny ceramic still blocks low-frequency signals. Students, RF designers, power-supply engineers, and lab technicians use that single formula daily to size decoupling caps, estimate AC current through a coupling capacitor, and convert datasheet farads into ohms at mains or switching frequency. This capacitive reactance calculator accepts a positive frequency and a positive capacitance, evaluates the closed-form expression with deterministic floating-point arithmetic, and returns Xc in ohms together with angular frequency omega equals two pi f, cleaned inputs, and a short printable expression. Zero frequency is rejected with a clear validation error because the formula would divide by zero; zero or negative capacitance is rejected for the same physical reason.
How a capacitor resists alternating current
A capacitor stores charge and cannot pass steady DC, but under a sinusoidal drive its voltage and current are related by a magnitude that behaves like a resistance that depends on frequency. Starting from the phasor relation I equals j omega C V, the impedance of an ideal capacitor is one over j omega C, whose magnitude is Xc equals one over omega C, and with omega equals two pi f that becomes the textbook formula Xc equals one over two pi f C.
The unit is the ohm: when f is in hertz and C is in farads, Xc is in ohms, so one microfarad at sixty hertz is about two thousand six hundred fifty-three ohms, while the same microfarad at one megahertz is only about zero point one six ohms. Doubling frequency or capacitance halves reactance; that inverse relationship is why filter corners, snubbers, and AC-coupling networks are specified as products of C and f rather than as a fixed resistance.
Real parts add equivalent series resistance, inductance, and dielectric loss that matter at the highest frequencies, but the first design step is still the ideal Xc from the nominal C and the signal frequency of interest. Inductive reactance XL equals two pi f L, impedance of series RC, and time-domain RC charging are different search intents and belong on separate landings so this page stays focused on the pure capacitive-reactance magnitude.
What you send and what you get back
Send a finite positive frequency under the field frequency, expressed in hertz, and a finite positive capacitance under the field capacitance, expressed in farads. Numeric values and numeric strings are both accepted so form widgets and spreadsheet paste stay convenient; SI prefix strings such as one kilohertz written as text are not parsed, so pass one thousand for a kilohertz tone and one times ten to the minus six for a microfarad part.
Capacitance must also be greater than zero; NaN, Infinity, and negative values fail the same way and are not charged. Classic classroom checks include sixty hertz with one hundred microfarads giving about twenty-six point five ohms, and one kilohertz with one microfarad giving about one hundred fifty-nine point one five ohms. If you need inductive reactance, series impedance, RC time constants, or stored charge, treat those as separate tools rather than extending this pure Xc magnitude.
Where capacitive reactance calculators show up in real work
Introductory AC circuit labs constantly assign Xc drills so students can convert microfarads and mains or audio frequencies into ohms before they measure current and phase on a scope or LCR meter. Power electronics and SMPS teams estimate ripple-current stress and snubber impedance by evaluating Xc of filter capacitors at the switching frequency, and a trusted closed form keeps notebooks and spreadsheets aligned.
Audio and RF designers size coupling and bypass capacitors by requiring Xc much smaller than the load or source impedance at the lowest frequency of interest, which is exactly one over two pi f C rearranged. Keep inductive-reactance, full impedance, time-constant, and charge-only landings separate so each search intent has one clear page rather than an overloaded multi-formula tool that confuses both students and search engines.
What you can do with it
Lab homework and AC circuit drills
Convert a capacitor value and a signal frequency into Xc in ohms so students can predict AC current before measuring phase and magnitude.
Decoupling and filter capacitor sizing
Check that Xc of a bypass or filter capacitor is low enough at the switching or audio frequency of interest for the design target impedance.
FAQ
What happens if frequency is zero?
Frequency must be a finite number strictly greater than zero.
Why does reactance fall when frequency rises?
Xc is inversely proportional to f. At higher frequency the capacitor has less time between polarity changes, so it passes more AC current and its effective opposition in ohms drops.
What units should I use?
Frequency in hertz and capacitance in farads. Example: 60 Hz × 100 µF (0.0001 F) → Xc ≈ 26.53 Ω. Pass SI values as numbers (e.g. 1000 and 1e-6); prefix strings like '1k' or '1uF' are not parsed.
What does it cost?
The browser tool is free and runs locally.
How much reactance does a 1 µF capacitor have at 60 Hz?
About 2653 ohms. The same microfarad at one megahertz drops to a fraction of an ohm, which is why one part can block a mains-frequency signal and still pass a fast one almost freely.
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
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/capacitive-reactance \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"frequency":60,"capacitance":0.0001}'const res = await fetch("https://api.kit.forhosting.com/elec/capacitive-reactance", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"frequency": 60,
"capacitance": 0.0001
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/capacitive-reactance",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"frequency": 60,
"capacitance": 0.0001
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/capacitive-reactance", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"frequency":60,"capacitance":0.0001}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"frequency":60,"capacitance":0.0001}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/capacitive-reactance", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"frequency": 60,
"capacitance": 0.0001
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.capacitive_reactance",
"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
Published price — no tokens, no invented credits. A failed task is never charged.
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 you send and what you get back
The same frequency is accepted under the aliases f, freq, or hz, and capacitance under c, C, or farads, but only one key may appear for each quantity in a request. Frequency must be strictly greater than zero because Xc equals one over two pi f C divides by f; zero frequency fails with invalid_input and a message that division by zero is not allowed. On success the response includes cleaned frequency and capacitance, reactance, capacitive_reactance, xc, and ohms as the same Xc value, angular_frequency as two pi f, unit set to ohm, a short expression string showing the formula with numbers, method capacitive_reactance, and the formula string Xc equals one over two pi f C. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where capacitive reactance calculators show up in real work
Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.
Integration use cases
CI fixtures and answer keys
Script the same Xc = 1/(2πfC) product used in the browser so automated graders and BOM checks share one ground truth for reactance.
Technical questions
What formula does this capacitive reactance calculator use?
Xc = 1 / (2 · π · f · C), with frequency f in hertz, capacitance C in farads, and result Xc in ohms. Angular frequency ω = 2πf is also returned so you can write Xc = 1/(ωC).