Coral reefs occupy less than 0.1% of the world’s ocean area.
That tiny share makes coral reefs remarkable: despite covering only about 284,300 square kilometres, they create complex habitats that support a large proportion of marine life. The commonly cited estimate is just under 0.1% of the oceans’ surface area, so the answer is not 1%, 5%, or 10%.
Most shallow-water reef-building corals grow in warm, sunlit seas. Their main distribution lies roughly between 30 degrees north and 30 degrees south of the equator, and tropical corals generally do not grow deeper than about 50 metres because they depend on light-reliant symbiotic algae. Many reefs also need temperatures near the mid-20s Celsius and clear, nutrient-poor water.
The Indo-Pacific contains about 91.9% of the world’s coral-reef area. Southeast Asia accounts for roughly 32.3% of the total, while the Pacific—including Australia—accounts for about 40.8%. Coral reefs are therefore geographically concentrated ecosystems, not a broadly distributed layer across the ocean. Their small area contrasts sharply with their ecological importance and vulnerability to warming, pollution, and ocean acidification.