Microeconomics
Four-Firm Concentration Ratio Calculator
Measure the combined market share controlled by the four largest firms.
Inputs and results stay in this browser. Currency symbols are illustrative; use any consistent currency.
Understand Four-firm concentration
One idea, three depths
Choose how deeply to explain Four-firm concentration
Four-firm concentration: Measure the combined market share controlled by the four largest firms.
Age 5Explain it to a 5-year-oldStart with a picture
Imagine using Four-firm concentration to answer this question: measure the combined market share controlled by the four largest firms? Enter Largest firm share, Second-largest firm share, Third-largest firm share, and 1 other input; the calculator shows Four-firm concentration ratio. For example: Market shares of 35%, 25%, 20% and 12% produce a four-firm concentration ratio of 92%. The answer tells you Four-firm concentration ratio.
Age 15Explain it to a 15-year-oldConnect it to the formula
CR4 is an intuitive concentration measure, but unlike HHI it does not distinguish how market share is distributed among the leading four firms. The rule is CR4 = Share of firm 1 + Share of firm 2 + Share of firm 3 + Share of firm 4. Its input values are Largest firm share (%), Second-largest firm share (%), Third-largest firm share (%), Fourth-largest firm share (%), and the main result is Four-firm concentration ratio. For example: Market shares of 35%, 25%, 20% and 12% produce a four-firm concentration ratio of 92%.
CollegeExplain it at college levelState the model precisely
This calculator evaluates a microeconomics relationship while holding unmodelled conditions constant. The implemented relation is CR4 = Share of firm 1 + Share of firm 2 + Share of firm 3 + Share of firm 4, evaluated from Largest firm share (%), Second-largest firm share (%), Third-largest firm share (%), Fourth-largest firm share (%) to produce Four-firm concentration ratio. CR4 is an intuitive concentration measure, but unlike HHI it does not distinguish how market share is distributed among the leading four firms. The result depends on comparable definitions, units, populations and time periods. It estimates a relationship; it does not establish causation or replace current primary data.
The economic question
Measure the combined market share controlled by the four largest firms.
Why this relationship is useful
CR4 is an intuitive concentration measure, but unlike HHI it does not distinguish how market share is distributed among the leading four firms.
Inputs that must be comparable
- Largest firm share (minimum 0) measured in %.
- Second-largest firm share (minimum 0) measured in %.
- Third-largest firm share (minimum 0) measured in %.
- Fourth-largest firm share (minimum 0) measured in %.
Use one market, firm, population and time period throughout; mixing definitions can make a correctly calculated number economically meaningless.
The model
CR4 = Share of firm 1 + Share of firm 2 + Share of firm 3 + Share of firm 4
From inputs to output
The calculator combines Largest firm share, Second-largest firm share, Third-largest firm share, Fourth-largest firm share and reportsFour-firm concentration ratio together with Share outside the four largest. Change one assumption at a time to identify what actually drives the estimate.
How to read Four-firm concentration ratio
Read the sign, magnitude, unit and period together. The result quantifies the relationship in “measure the combined market share controlled by the four largest firms”; it does not by itself prove that one input caused another.
A worked economic example
Market shares of 35%, 25%, 20% and 12% produce a four-firm concentration ratio of 92%.
Where interpretation can fail
Do not use the result when the input definitions, units or formula assumptions do not match the real situation. This is an educational model, not financial, investment, tax or policy advice; verify material decisions against primary data and professional guidance.
Supporting sourcesAcademic referencesPrimary standards, textbooks and complete citations
Standards, reading and academic references
Use the calculator as the worked interaction, then consult the primary standards and academic textbooks listed below. MW SysArc links to the original sources; the explanation on this page is original and does not reproduce them.
Principles of Economics 3e
Read the free OpenStax economics textbookCite this book
- APA 7
- Greenlaw, S. A., Shapiro, D., & MacDonald, D. (2022). Principles of economics 3e. OpenStax. https://openstax.org/books/principles-economics-3e/pages/1-introduction
- MLA 9
- Greenlaw, Steven A., et al. Principles of Economics 3e. OpenStax, 2022, https://openstax.org/books/principles-economics-3e/pages/1-introduction.
- Chicago author-date
- Greenlaw, Steven A., David Shapiro, and Daniel MacDonald. 2022. Principles of Economics 3e. Houston, TX: OpenStax. https://openstax.org/books/principles-economics-3e/pages/1-introduction.
OpenStax entries are free to read online. Follow the licence shown on each linked source before redistributing or adapting its content.
Reuse the page responsiblyCite this pageAPA, MLA, Chicago, Harvard, BibTeX and RIS
These formats cite this calculator page itself. They are separate from the academic references above, which support the mathematical method and terminology.
APA 7
MW SysArc. (2026, July 21). Four-Firm Concentration Ratio Calculator. MW SysArc Tools. https://economics.mwsysarc.com/micro/four-firm-concentration-ratio
MLA 9
MW SysArc. “Four-Firm Concentration Ratio Calculator.” MW SysArc Tools, 21 July 2026, https://economics.mwsysarc.com/micro/four-firm-concentration-ratio. Accessed 31 Aug. 2026.
Chicago 17
MW SysArc. “Four-Firm Concentration Ratio Calculator.” MW SysArc Tools. Published July 21, 2026. Accessed August 31, 2026. https://economics.mwsysarc.com/micro/four-firm-concentration-ratio.
Harvard
MW SysArc (2026) ‘Four-Firm Concentration Ratio Calculator’, MW SysArc Tools. Published 21 July 2026. Available at: https://economics.mwsysarc.com/micro/four-firm-concentration-ratio (Accessed: 31 August 2026).
BibTeX and RIS records
BibTeX
@misc{mwsysarc_four_firm_concentration_2026,
author = {{MW SysArc}},
title = {Four-Firm Concentration Ratio Calculator},
howpublished = {MW SysArc Tools},
year = {2026},
url = {https://economics.mwsysarc.com/micro/four-firm-concentration-ratio},
note = {Published July 21, 2026; accessed August 31, 2026}
}RIS
TY - ELEC
AU - MW SysArc
TI - Four-Firm Concentration Ratio Calculator
T2 - MW SysArc Tools
PY - 2026
DA - 2026-07-21
Y2 - 2026-08-31
UR - https://economics.mwsysarc.com/micro/four-firm-concentration-ratio
N1 - Published July 21, 2026
ER -Clear answers
Frequently asked questions
What does the Four-firm concentration do?
Measure the combined market share controlled by the four largest firms.
How does the Four-firm concentration work?
The calculator applies this formula: CR4 = Share of firm 1 + Share of firm 2 + Share of firm 3 + Share of firm 4. CR4 is an intuitive concentration measure, but unlike HHI it does not distinguish how market share is distributed among the leading four firms.
What can I learn from the Four-firm concentration?
It helps you explore the relationship described by this tool: Measure the combined market share controlled by the four largest firms. Change one input at a time to observe how it affects the result.
Does MW SysArc receive or store what I enter?
No. The calculation runs locally in your browser. MW SysArc does not receive or store your calculation inputs.
How should I use the result?
Use the result as an estimate or educational aid. Check important financial, business or policy decisions with qualified sources and current data.
Last reviewed . Calculations tested .