N-firm concentration ratio calculator
A market of 6 firms whose four leaders hold 90% of sales has a CR4 of 90%, rated highly concentrated. Enter any list of firm shares and choose how many leaders to add, such as four or eight, to get the ratio and its band. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Shares
- 40, 25, 15, 10, 6, 4
- N
- 4
- Firm count
- 6
- Share unit
- Percent
- Crn label
- CR4
- Top n shares
- 40, 25, 15, 10
The N-firm concentration ratio, written CR_n, is the industrial-organization staple that answers a single question: how much of a market sits with its largest sellers. Rank every listed firm share from largest to smallest and add the first N of them. A CR4 of ninety percent means the four biggest firms together hold ninety percent of sales; a CR8 near forty percent describes a much more fragmented industry. This N-firm concentration ratio calculator accepts a list of firm market shares and the integer N, sorts the shares, sums the N largest, and returns the ratio in the same unit you sent plus a percent form and a coarse classroom band.
What the N-firm concentration ratio measures and how the ranking works
The N-firm concentration ratio is one of the oldest structural measures taught in industrial organization. Write the market shares of the firms you have, rank them from largest to smallest, and add the first N entries: that sum is CR_n. When N is four the statistic is the familiar CR4; when N is eight it is CR8.
Because the ranking uses the largest sellers first, two industries with the same number of firms can have very different ratios if one of them is dominated by a handful of leaders. Shares may be written as percents that add to at most one hundred or as proportions that add to at most one; the arithmetic is the same either way.
A market whose four largest firms hold forty, twenty-five, fifteen and ten percent has CR4 equal to ninety percent and would be described in a principles classroom as highly concentrated. A market whose four largest firms hold twelve, ten, eight and six percent has CR4 equal to thirty-six percent and sits in a much more competitive band.
This calculator does not invent fringe firms you did not list: it ranks only the shares you send and rejects a request when N is larger than that list, rather than silently padding with zeros that would understate concentration. Ties keep their original order after a stable descending sort so two firms with the same share produce a reproducible top-N set.
The result is a single additive index, not a squared-share index such as the Herfindahl–Hirschman index; CR_n answers how much of the market the N largest firms hold together, which is a different question from how unevenly the whole share vector is distributed across every firm.
Where an N-firm ratio is useful
Principles and industrial-organization courses use an N-firm concentration ratio calculator so learners can turn any valid share vector into CR4, CR8, or another CR_n without sorting by hand or mixing percent shares with proportions. Exam generators and LMS plugins need a deterministic oracle that rejects an N larger than the firm list instead of inventing a hollow success that a buggy grader might treat as a complete market. Failed validation does not consume balance.
Keep requests small, pin the rounded ratio and band in tests, and you get reproducible CR_n figures for homework, LMS plugins, and edge workers without standing up an industrial-organization simulation stack of your own.
What you can do with it
Classroom CR4 and CR8 checks
Let students enter a vector of firm market shares and N, then verify the ranked top-N sum against textbook CR4 and CR8 worked examples.
LMS and exam auto-grading
Mark N-firm concentration-ratio items with a deterministic oracle that rejects N larger than the listed firms and negative shares.
Industry structure notebooks
Batch-compute CR_n across markets from the same share tables without spreadsheet sort drift or mixed percent and proportion units.
FAQ
How is the N-firm concentration ratio calculated?
Rank the listed firm market shares from largest to smallest and add the first N. Send shares plus n.
What does a high CR4 mean?
A high CR4 means the four largest listed firms hold most of the market.
What if N is larger than the number of firms I listed?
The calculator will not pad missing firms with zeros, because that would understate CR_n relative to a complete list.
Can I enter shares as proportions instead of percents?
Yes. Choose proportions and enter each share as a value up to 1, with the list adding up to no more than 1. The ratio comes back in the same unit, plus a percent version for charts.
How is the N-firm ratio different from the Herfindahl index?
The N-firm ratio simply adds the shares of the largest N firms. The Herfindahl index squares every firm's share, so it measures how unevenly the whole market is split, which is a different question.
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/econ/concentration-ratio-crn \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"shares":[40,25,15,10,6,4],"n":4}'const res = await fetch("https://api.kit.forhosting.com/econ/concentration-ratio-crn", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"shares": [
40,
25,
15,
10,
6,
4
],
"n": 4
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/econ/concentration-ratio-crn",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"shares": [
40,
25,
15,
10,
6,
4
],
"n": 4
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/econ/concentration-ratio-crn", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"shares":[40,25,15,10,6,4],"n":4}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"shares":[40,25,15,10,6,4],"n":4}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/econ/concentration-ratio-crn", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"shares": [
40,
25,
15,
10,
6,
4
],
"n": 4
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "econ.concentration_ratio_crn",
"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.
Limits
max_items | 10000 |
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
Input contract, units, response fields, and validation
POST a JSON body with two required fields: shares, a non-empty array of non-negative finite firm market shares, and n, a positive integer equal to how many of the largest firms to include. Optionally send share_unit as percent or proportion (default percent) and decimals as an integer from zero through twelve (default six) to control half-up rounding. When share_unit is percent each share must be at most one hundred and the list must sum to at most one hundred. When share_unit is proportion each share must be at most one and the list must sum to at most one. n cannot exceed the length of shares; asking for CR8 when you listed only five firms is invalid_input, not a sum of the five plus three invented zeros. Missing fields, empty arrays, negative shares, non-integer n, non-finite values, and a share_unit outside the closed enum fail the same way and are not billed. Common aliases are accepted: market_shares, firm_shares, or values for shares, and top_n or k for n. On success the body returns n, firm_count, share_unit, crn_label such as CR4, top_n_shares in descending order, concentration_ratio in the unit you sent, concentration_ratio_percent on a zero-to-one-hundred scale, total_share of every listed firm, unlisted_share as the leftover up to the unit maximum, concentration_band as a classroom label (unconcentrated below forty percent, moderately_concentrated below sixty, concentrated below eighty, highly_concentrated at eighty and above), and formula. Example: shares forty, twenty-five, fifteen, ten, six, four with n equal to four yields CR4 equal to ninety percent and highly_concentrated. Pair the number with your own Herfindahl calculation if you need a squared-share index; this endpoint computes only the additive N-firm sum.
Where an N-firm concentration ratio API earns its keep
Consulting notebooks and competition worksheets often tabulate CR_n across industries from the same published share tables; pinning the rank-and-sum step in a tiny parse API keeps spreadsheet sort drift out of the comparison column. Official United States merger guidelines today lean on the Herfindahl–Hirschman index rather than CR_n, so treat the returned concentration_band as a classroom heuristic, not a legal finding, and compute HHI separately when a filing or guideline screen is the real question.
Technical questions
Can I send shares as proportions instead of percents?
Yes. Set share_unit to proportion and send shares on the unit interval (each at most 1, list summing to at most 1). Default share_unit is percent.
What does the N-firm concentration ratio calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.