Series resistance calculator
100 Ω, 220 Ω and 330 Ω in series add up to 650 Ω. List the resistors in a single current path and get the one total that replaces the whole chain, for current limiters, divider legs or lab checks. Free in your browser.
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- Your data stays on your device
Run — free
Runs in your browser. Free, unlimited — your data never leaves this page.
When resistors share a single current path they form a series circuit, and the total resistance is simply the sum of every individual value measured in ohms. Students, hobbyists, and technicians use that sum every day to size current-limiting parts, check voltage-divider legs before a parallel branch is added, and confirm that a chain of preferred E-series values still meets a design budget. This series resistance calculator accepts a list of non-negative resistor values, adds them with deterministic floating-point arithmetic, and returns the total resistance together with a cleaned copy of the inputs and a short printable expression. Negative numbers are rejected with a clear validation error because passive resistors cannot contribute negative ohms; zero is allowed for an ideal wire or fuse placeholder in the string.
How series resistance works
In a pure series string every resistor carries the same current, while the voltage drops across each part add to the source voltage. Ohm's law applied to the whole string then gives V equals I times R_total, so the only unknown left is the equivalent resistance that replaces the entire chain. Preferred decade values such as one hundred, two hundred twenty, and three hundred thirty ohms add cleanly to six hundred fifty ohms and remain easy to stock.
When a design later needs a parallel combination instead, the reciprocal sum one over R equals the sum of one over Ri is a different search intent and a different landing page; do not overload this series calculator with parallel logic.
Where series resistance calculators show up in real work
Introductory electronics labs constantly assign series chains so students can verify that measured multimeter readings match the sum of color-code values before they move on to parallel and series-parallel reductions. Firmware and hardware bring-up teams size current-limiting resistors for LEDs, pull-ups, and sense paths by adding preferred E12 or E24 values until the total meets a budget, then record the chosen list for the bill of materials.
Repair technicians reconstructing a failed voltage divider often rebuild the series string from scrap values and need a trusted total before powering the board. Keep parallel-only, Wheatstone, and delta-star conversion landings separate so each search intent has one clear page rather than a overloaded multi-topology tool that confuses both students and search engines.
What you can do with it
Lab homework and color-code checks
Sum a series string of preferred ohm values so students can compare the calculated total against a multimeter reading before learning parallel combinations.
LED and pull-up current limiting
Add stocked E-series resistors until the series total meets a current or voltage budget, then lock the list into the bill of materials.
FAQ
What formula does this series resistance calculator use?
Every resistor in a pure series string contributes its ohm value to a single arithmetic sum.
What happens if a resistor value is negative?
Negative resistance is not allowed for passive series resistors; each value must be greater than or equal to zero ohms.
Are zero-ohm resistors allowed?
Yes. A zero entry is treated as an ideal wire or fuse placeholder in the series string and does not change the total.
Does this calculator handle parallel resistors?
No. Parallel equivalent resistance uses 1/R = Σ 1/Ri and is a different search intent. Use a dedicated parallel resistance tool for that topology.
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/resistors-series \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"resistors":[100,220,330]}'const res = await fetch("https://api.kit.forhosting.com/elec/resistors-series", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"resistors": [
100,
220,
330
]
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/resistors-series",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"resistors": [
100,
220,
330
]
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/resistors-series", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"resistors":[100,220,330]}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"resistors":[100,220,330]}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/resistors-series", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"resistors": [
100,
220,
330
]
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.resistors_series",
"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 series resistance works
Empty lists fail validation because there is nothing to sum, and lists longer than ten thousand entries are rejected so a single request cannot monopolize a free Worker slice.
What you send and what you get back
Send a non-empty list of finite resistor values under the field resistors, expressed in ohms. Classic classroom checks include one hundred plus two hundred twenty plus three hundred thirty equaling six hundred fifty, a single resistor returning itself, and a zero-ohm entry that leaves the total unchanged. If you need power dissipation, voltage drop per resistor, or a full mesh reduction of mixed series-parallel networks, treat those as separate tools rather than extending this pure series sum. The same list is accepted under the aliases values, r, or ohms, but only one of those keys may appear in a request. Arrays of numbers, JSON array strings, and comma or semicolon separated text are all accepted so spreadsheet paste and form widgets stay convenient. Every entry must be a finite number greater than or equal to zero; NaN, Infinity, and negative ohms fail with invalid_input and are not charged. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where series resistance 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
BOM and fixture regression
Script the same series sum used in the browser so CI fixtures assert that programmed resistor ladders still match the design document.