Capacitor voltage rating selector
A 12 V rail needs a capacitor rated for at least 24 V under the default 0.5 derating factor, so the tool picks a standard 25 V part. Enter the working voltage, and your own factor if your rule is different. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Continuous DC
- 12
- Derating factor
- 0.5 V
- Min voltage rating
- 24
- Recommended voltage rating
- 25
- Headroom ratio
- 2.0833333333
Choosing a capacitor voltage rating is not the same as reading the DC bus voltage on a schematic. Parts that sit at full rated stress age faster, leak more, and fail earlier—especially aluminum electrolytics and some film types—so designers apply a derating margin and then step up to a commercial voltage ladder. This capability takes your continuous working voltage, divides by a derating factor (default half of rated voltage, the common long-life rule of thumb), and returns the smallest standard DC rating that meets or exceeds that minimum. The result is deterministic: students, BOM reviewers, and design automations get the same recommendation every time for homework, design reviews, or pipeline checks without spreadsheets that quietly mix volts and percentages.
Why derate capacitor voltage for long-term reliability
A capacitor’s marked voltage is the manufacturer’s absolute continuous rating under specified conditions, not a target operating point. Running near that limit raises electric field stress inside the dielectric, accelerates electrolyte dry-out in wet aluminum types, and can worsen leakage or capacitance drift over thousands of hours.
Industry practice therefore keeps continuous working voltage well below the nameplate: a fifty-percent derating factor means the part should be rated for at least twice the bus voltage, while more conservative or more aggressive factors appear for high-temperature environments, ceramics with voltage-dependent capacitance, or cost-constrained rails.
This tool does not replace datasheet graphs for lifetime versus temperature and ripple; it implements the first sizing step every schematic review asks for—map working voltage through a clear stress fraction to a purchasable rating—so you can document why a twenty-five volt part was chosen for a twelve volt rail instead of a ten volt part that looked close enough on paper.
Where this fits in design reviews, education, and automation
Electronics courses use a capacitor voltage rating selector to turn textbook derating rules into a concrete part number class without fragile calculator apps that mix percent margin with stress ratio. Hardware teams running design-for-reliability reviews batch-check power rails, bias networks, and bulk input capacitors against a house standard factor and store the recommended rating beside the schematic reference. Pair the result with capacitance derating, ripple current, ESR, and temperature rise checks in your own flow when you need full reliability sign-off beyond voltage alone.
What you can do with it
BOM and schematic reviews
Map each rail’s continuous voltage through your house derating factor to the next standard capacitor rating before layout freeze.
Homework and reliability labs
Apply textbook 50% or 70% voltage derating rules and show the selected commercial voltage class in lab reports.
Substitution checks
Reject or accept alternate capacitors by comparing their voltage rating against the computed minimum for the working bus.
FAQ
What formula does the capacitor voltage rating selector use?
The recommended rating is the smallest standard DC ladder value greater than or equal to that minimum.
What is the default derating factor?
0.5, meaning continuous working voltage should not exceed half the rated voltage (at least 2× headroom).
Does this account for temperature or ripple current?
No. It only maps working voltage through a stress factor to a standard voltage class. Use manufacturer lifetime curves for temperature, ripple, and ESR limits.
Why does a 12 V rail get a 25 V capacitor and not a 16 V one?
With the default factor of 0.5 the part must be rated for at least 24 V, twice the working voltage. The next standard rating at or above that is 25 V, so 16 V and 20 V parts fall short of the margin.
What voltage should I enter when AC rides on top of the DC?
Enter the peak of the DC-biased waveform, not only the DC level. That peak is the stress the capacitor really carries, so it is the working voltage the derating has to start from.
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-voltage-rating \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"working_voltage":12}'const res = await fetch("https://api.kit.forhosting.com/elec/capacitor-voltage-rating", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"working_voltage": 12
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/capacitor-voltage-rating",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"working_voltage": 12
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/capacitor-voltage-rating", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"working_voltage":12}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"working_voltage":12}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/capacitor-voltage-rating", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"working_voltage": 12
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.capacitor_voltage_rating",
"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
How the selector computes minimum rating and picks the ladder
Pass working_voltage as the continuous DC voltage the capacitor will see, or the peak DC-biased value when AC is superimposed, in volts. Optionally pass derating_factor between zero exclusive and one inclusive; when omitted the default is zero point five, so the minimum rating is twice the working voltage. The engine computes min_voltage_rating equals working_voltage divided by derating_factor, then selects the smallest entry from a fixed commercial DC ladder—four, six point three, ten, sixteen, twenty, twenty-five, thirty-five, fifty, sixty-three, eighty, one hundred, and higher values through three thousand volts—that is greater than or equal to that minimum. The response echoes both inputs, reports headroom_ratio as recommended over working and stress_ratio as working over recommended, and includes the formula string for audit logs. Aliases such as Vw, voltage, factor, and derate are accepted so API clients and spreadsheet columns need no rename step. Non-positive working voltage, non-finite numbers, and factors outside the open-closed interval zero to one fail with invalid_input and are never charged.
Where this fits in design reviews, education, and automation
Because the implementation is pure analytic JavaScript with no AI and no external APIs, browser preview and paid API results match after stable rounding. Bill only successful API calls at $0.002 per request; missing fields or invalid voltages fail fast without consuming balance.
Technical questions
What happens if working voltage is zero or negative?
The request fails with invalid_input stating that working_voltage must be positive. Failed tasks are not charged.
How much does the API cost?
$0.002 per successful request. The on-page tool runs free in your browser with the same analytic core.