Capacitor charge calculator
A 1 µF capacitor held at 5 V stores 5 µC, and this calculator gives that product of capacitance and voltage in coulombs. Zero farads returns zero, and a negative voltage returns a signed charge for reverse polarity. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Capacitance in farads
- 0.000001
- Voltage
- 5
- Charge
- 0.000005 coulomb
- Charge coulombs
- 0.000005
- Expression
- 0.000001 F × 5 V = 0.000005 C
A capacitor stores electric charge on a pair of conductors separated by a dielectric, and the amount of charge is tied to the voltage across the device by the defining relation Q equals C times V. Students, hobbyists, and design engineers use that product every day to size decoupling parts, check pulse-energy budgets, and convert between microfarad-scale datasheet values and coulomb-scale charge estimates. This capacitor charge calculator accepts a non-negative capacitance in farads and a finite applied voltage in volts, multiplies them with deterministic floating-point arithmetic, and returns the stored charge in coulombs together with cleaned inputs and a short printable expression. Negative capacitance is rejected with a clear validation error because a passive capacitor cannot have C less than zero; zero farads is allowed and simply yields zero charge. Negative voltage is accepted and produces a signed charge that reflects reverse polarity.
How capacitor charge relates to capacitance and voltage
By definition the capacitance C of a two-terminal device is the constant of proportionality between the free charge Q on one plate and the potential difference V between the plates, written Q equals C times V when C is expressed in farads, V in volts, and Q in coulombs.
That linear relation is the small-signal idealization used in almost every introductory circuit course and in first-pass power-rail design: a one-microfarad capacitor held at five volts stores five microcoulombs, and a one-farad supercapacitor at two and a half volts stores two and a half coulombs. The formula does not depend on the path used to reach that voltage, so a slow ramp, a constant current, or a step followed by settling all end at the same Q for the same final V on an ideal capacitor.
Real parts have leakage, dielectric absorption, voltage-dependent capacitance, and tolerance bands, but the first design step is still the arithmetic product of the nominal C and the applied V. Energy stored is a different quantity given by one half C V squared and belongs on a separate landing so search intent for charge does not collide with search intent for joules.
Series and parallel capacitor networks change the equivalent C before you apply Q equals C V; this tool takes the already-known equivalent capacitance and the terminal voltage rather than solving a multi-branch network.
What you send and what you get back
Send a finite non-negative capacitance under the field capacitance, expressed in farads, and a finite voltage under the field voltage, expressed in volts. Numeric values and numeric strings are both accepted so form widgets and spreadsheet paste stay convenient; SI prefix strings such as one microfarad written as text are not parsed, so pass one times ten to the minus six for a microfarad part. Voltage may be positive, negative, or zero.
Classic classroom checks include one microfarad at five volts equaling five microcoulombs, one farad at twelve volts equaling twelve coulombs, and a negative voltage that yields a negative signed charge. If you need stored energy, RC discharge times, impedance at a given frequency, or series-parallel reduction of capacitor banks, treat those as separate tools rather than extending this pure Q equals C V product.
Where capacitor charge calculators show up in real work
Introductory electronics labs constantly assign Q equals C V drills so students can convert between datasheet microfarads and coulomb-scale charge before they move on to energy and RC transients. Power-electronics and embedded bring-up teams size bulk and decoupling capacitors by estimating the charge needed to cover a load current for a short hold-up interval, then convert that charge budget into a minimum C at the allowed voltage droop.
Supercapacitor and energy-harvesting designs quote available charge and coulomb capacity at a working voltage, and a trusted product of C and V keeps datasheet checks and lab notebooks aligned. Keep energy-only, impedance, and multi-capacitor network 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 datasheet checks
Convert a datasheet capacitance and a bias voltage into stored charge in coulombs so students can verify multimeter and scope estimates against Q = C × V.
Hold-up and decoupling charge budgets
Estimate how many coulombs a bulk capacitor can supply during a brief current draw by multiplying C by the allowed voltage window.
FAQ
What formula does this capacitor charge calculator use?
Q = C × V. Capacitance C is in farads, voltage V in volts, and the stored charge Q is returned in coulombs.
What happens if capacitance is negative?
Passive capacitance must be ≥ 0 farads; negative C is rejected and is not charged.
Can voltage be negative?
Yes. Negative voltage is treated as reverse polarity and yields a signed (negative) charge. Zero voltage yields zero charge.
Do I pass microfarads or farads?
Always farads in SI base units. For 1 µF pass 1e-6 (or 0.000001). Prefix strings like "1uF" are not parsed.
What does it cost?
The browser tool is free and runs locally.
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/capacitor-charge \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"capacitance":0.000001,"voltage":5}'const res = await fetch("https://api.kit.forhosting.com/elec/capacitor-charge", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"capacitance": 0.000001,
"voltage": 5
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/capacitor-charge",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"capacitance": 0.000001,
"voltage": 5
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/capacitor-charge", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"capacitance":0.000001,"voltage":5}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"capacitance":0.000001,"voltage":5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/capacitor-charge", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"capacitance": 0.000001,
"voltage": 5
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.capacitor_charge",
"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 capacitance is accepted under the aliases c, C, or farads, and voltage under v, V, or volts, but only one key may appear for each quantity in a request. Capacitance must be greater than or equal to zero; NaN, Infinity, and negative farads fail with invalid_input and are not charged. On success the response includes cleaned capacitance and voltage, charge and charge_coulombs as the same product, unit set to coulomb, a short expression string of the form C F times V V equals Q C, method q_equals_cv, and the formula string Q equals C times V. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where capacitor charge 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 Q = C × V product used in the browser so automated graders and BOM checks share one ground truth for charge.