What Is Market Concentration? #
Market concentration measures how much of an industry's total revenue is controlled by its largest firms. It is the single most informative metric about an industry's competitive structure, revealing whether a market is dominated by a few large operators or split among hundreds of thousands of small ones.
Two standard measures dominate. The CR4 ratio is the combined market share of the top four firms. The Herfindahl-Hirschman Index (HHI) is the sum of every firm's squared market share. CR4 is the more intuitive of the two and the one most industry analysts quote. HHI is the measure the Department of Justice and Federal Trade Commission actually use to review mergers.
Both are published directly by the US Census Bureau in the Economic Census concentration tables. They are not estimates or model outputs: they are counted from a mandatory survey covering the full universe of US employer firms in each industry.
How to Calculate CR4 and HHI #
HHI = the sum of (market share)² across every firm in the industry
The squaring is what makes HHI different. A single firm holding 40% contributes 1,600 points on its own; four firms holding 10% each contribute 400 points between them. HHI therefore rises when one firm pulls ahead of the pack, while CR4 cannot tell the difference between four evenly matched rivals and one giant with three minnows.
HHI thresholds (2023 Merger Guidelines)
| HHI | Official designation |
|---|---|
| Below 1,000 | Unconcentrated |
| Above 1,000 | Concentrated |
| Above 1,800 | Highly concentrated |
CR4 bands (analyst convention, not a legal standard)
| CR4 | Common description |
|---|---|
| Below 40% | Fragmented |
| 40% to 60% | Moderately consolidated |
| Above 60% | Consolidated |
Where the numbers come from. Both ratios are published by the US Census Bureau in the Economic Census concentration table, which reports the share of industry receipts held by the largest 4, 8, 20 and 50 firms, plus HHI. Figures are national, drawn from the 2022 Economic Census, with 2017 used where 2022 is not yet published for an industry.
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Fragmented vs Concentrated: Two Real Industries #
The clearest way to understand concentration is to put two real industries side by side. Both sets of figures below are published by the US Census Bureau for the same year, using the same method.
| Measure | Construction (23) | Scheduled air transport (4811) |
|---|---|---|
| Top 4 firms (CR4) | 2.6% | 69.8% |
| Top 8 firms (CR8) | 4.0% | 81.7% |
| Top 20 firms (CR20) | 6.8% | 93.0% |
| Top 50 firms (CR50) | 11.4% | 98.0% |
| HHI | 3.9 | 1,349.3 |
| Establishments | 814,557 | 2,233 |
Concentration: US Census Bureau, Economic Census 2022. Establishments: US Census Bureau, County Business Patterns 2023.
What this means in practice. A construction firm cannot move the market price. There is no plausible share of national output any single contractor can reach, so competition is won on cost control and local density. An airline operates inside a structure where four carriers set the terms, capacity decisions are visible to every rival, and a merger draws regulatory attention.
Market Concentration Examples #
Concentration varies more widely across US industries than any other structural metric. The ladder below spans almost the entire published range, from near-total fragmentation to a market held by four firms.
| Industry | NAICS | CR4 | HHI | Establishments |
|---|---|---|---|---|
| Specialty trade contractors | 238 | 1.8% | 1.7 | 521,315 |
| Construction | 23 | 2.6% | 3.9 | 814,557 |
| Warehousing and storage | 493 | 18.5% | 147.9 | 21,521 |
| Paper manufacturing | 322 | 32.5% | 348.3 | 3,813 |
| Pipeline transportation | 486 | 45.3% | 636.2 | 3,517 |
| Telecommunications | 517 | 64.7% | 1,248.4 | 58,992 |
| Scheduled air transportation | 4811 | 69.8% | 1,349.3 | 2,233 |
| Securities and commodity exchanges | 5232 | 95.1% | 2,434.7 | 54 |
Concentration: US Census Bureau, Economic Census 2022. Establishments: US Census Bureau, County Business Patterns 2023.
Note how poorly establishment count alone predicts concentration. Paper manufacturing and pipeline transportation are almost the same size by establishment count, 3,813 against 3,517, yet pipeline transportation's top four hold 45.3% of the market where paper's hold 32.5%. Securities and commodity exchanges reaches CR4 95.1% across just 54 establishments, while specialty trade contracting spreads 521,315 establishments across a CR4 of 1.8%. Counting competitors tells you how many exist; concentration tells you whether any of them matter.
Why CR4 and HHI Disagree #
Scheduled air transportation shows why you need both measures. Its CR4 is 69.8%, which reads like a near-monopoly. Its HHI is 1,349.3, which under the 2023 Merger Guidelines is merely concentrated, not highly concentrated. Both numbers are correct.
The reason is that CR4 counts only the combined size of the top four, while HHI registers how evenly that share is divided among them. Four carriers of roughly similar size produce a high CR4 and a mid-range HHI. One dominant carrier with three small rivals would produce the same CR4 and a far higher HHI. To a merger reviewer those are completely different markets.
Where you draw the industry boundary changes the answer
The same market measured one NAICS level apart produces materially different concentration:
| Definition | NAICS | CR4 | HHI |
|---|---|---|---|
| Air transportation (all) | 481 | 60.2% | 1,010.5 |
| Scheduled air transportation | 4811 | 69.8% | 1,349.3 |
Widening the definition to take in charter and non-scheduled operators drops HHI from 1,349.3 to 1,010.5, moving the industry from clearly concentrated to the edge of the threshold. This is why a concentration figure is only meaningful alongside the exact NAICS code it was measured at. A CR4 quoted without its code and its Economic Census year is not usable evidence.
Why Concentration Matters for Your Business #
| If your industry is... | Strategic implication |
|---|---|
| Fragmented (CR4 below 40%) | Compete on cost efficiency or niche focus. No single firm sets the market price. Consolidation opportunities exist for well-capitalised operators, and barriers to entry are likely low. |
| Moderately consolidated (CR4 40% to 60%) | Top players hold structural advantages. New entrants need real differentiation or capital to compete. M&A activity is usually rising. |
| Consolidated (CR4 above 60%) | Incumbents set the terms. Entry is difficult and expensive. Merger scrutiny increases, and pricing power is significant. |
For operators: concentration tells you how hard it will be to win and hold share. In fragmented markets share comes from operational excellence; in consolidated markets it is defended by structural barriers.
For investors: concentration is a leading indicator of margin durability. Consolidated industries support higher multiples because incumbent earnings are harder to compete away.
For acquirers: a fragmented industry with a low CR50 is the classic roll-up setting. Construction's fifty largest firms hold 11.4% of the market between them, and that single figure is the arithmetic behind every contractor consolidation thesis.
Where the Official Numbers Come From #
Every concentration figure on this page comes from one source: the US Census Bureau's Economic Census concentration table, which reports the share of industry receipts held by the largest 4, 8, 20 and 50 firms, along with HHI. It is collected every five years through a mandatory survey covering the full universe of US employer firms.
- Vintage. The 2022 Economic Census is the current release. Where 2022 is not yet published for an industry, the 2017 figures stand as the most recent official measurement.
- Geography. National only. Census does not publish state or metro level concentration, so any local CR4 you encounter is somebody's estimate rather than a federal figure.
- Coverage gaps. Not every industry receives every measure. Transit and ground passenger transportation has a published CR4 of 30.7% but no published HHI. Where Census suppresses a value to protect respondent confidentiality, no substitute exists and the honest answer is that the figure is unavailable.