The Amazon rainforest is the largest tropical rainforest in the world. It occupies a vast area of tropical South America and is centred on the Amazon Basin. Estimates of its area vary because different organisations and researchers use different definitions for rainforest, forest cover, biome boundaries and the wider Amazon region. WWF gives approximately 6.7 million square kilometres for the Amazon region in one current overview, while other definitions produce somewhat smaller or larger figures.
Guinness World Records gives approximately 6.56 million square kilometres for the rainforest under its specified definition. The Amazon is therefore unambiguously the world's largest tropical rainforest even though its exact measured area depends on the boundary being used. It is also the largest remaining tropical forest complex and forms a major component of the wider Amazon biome.
The Amazon rainforest spans eight South American countries and one overseas territory of France. These are Brazil, Peru, Colombia, Bolivia, Ecuador, Venezuela, Guyana, Suriname and French Guiana. Brazil contains the largest proportion, with nearly 60 percent of the Amazon region according to WWF UK. The rainforest is closely associated with the Amazon River and its enormous drainage basin, although the forest, biome and river basin are not exactly synonymous geographical entities.
The Amazon Basin is a hydrological region defined by drainage, while the Amazon biome includes multiple ecosystems and vegetation types, and the rainforest refers more specifically to the extensive tropical forest. This distinction matters because statements about the area of the Amazon can refer to different geographical boundaries and therefore produce different numerical estimates.
The Amazon's physical scale is extraordinary. WWF describes the Amazon basin as covering roughly 2.7 million square miles, approximately 40 percent of South America, while its dense forest area is described separately as about 2.2 million square miles in another WWF source. Other estimates use approximately 6.7 million square kilometres for the wider Amazon region. These figures are not necessarily contradictory because they refer to different boundaries and categories.
The basin includes rivers, wetlands, savannas, forests and other ecosystems, whereas a rainforest estimate attempts to identify the area dominated by tropical forest. Consequently, the most scientifically careful statement is that the Amazon is the largest tropical rainforest on Earth and covers several million square kilometres, while recognising that exact area depends on the definition used.
The Amazon is also one of the most biodiverse regions on the planet. WWF estimates that the Amazon biome contains about one in ten known species on Earth, with tens of thousands of plant species and thousands of fish, reptile and other animal species. The extraordinary diversity arises from the enormous geographical area, warm and wet climate, complex river networks, varied soils and habitats, long evolutionary history and extensive environmental gradients. Biodiversity is not distributed evenly across the forest.
Different parts of the basin contain distinct communities, and mountains, rivers and historical climatic refuges can promote geographic isolation and speciation. Many species are endemic, meaning they occur naturally in particular regions and nowhere else. The Amazon therefore has both exceptional species richness and exceptional importance for evolutionary diversity.
The Amazon plays a major role in the global carbon cycle but should not be described simplistically as an unlimited carbon sink. Its vegetation stores enormous quantities of carbon in trees, roots, litter and soils, while photosynthesis removes carbon dioxide from the atmosphere. At the same time, respiration, decomposition, fires, droughts and land use release carbon. Whether a particular Amazon region is a net sink or source depends on the balance among these processes over a specified period.
Deforestation converts living biomass into emissions and reduces future carbon uptake, while degradation can increase vulnerability to fire and drought. The Amazon therefore has major climate significance because its size means that changes in forest condition can affect both regional carbon cycling and atmospheric carbon concentrations.
The Amazon also influences the hydrological cycle. Forest vegetation releases water vapour through transpiration, while rainfall supplies water to plants, soils, wetlands and rivers. The forest and atmosphere interact through repeated moisture recycling, allowing rainfall generated or transported within the system to support distant parts of the basin and surrounding regions. The enormous Amazon River system then transports freshwater towards the Atlantic Ocean. Forest loss can alter evapotranspiration, surface energy balance, runoff and atmospheric moisture transport, potentially changing rainfall patterns.
The scale of the Amazon means that these effects are relevant beyond individual forest parcels. Its ecological importance therefore arises not only from the species living within the forest but also from its interaction with regional climate, atmospheric circulation, rivers and the wider South American water cycle.
The Amazon is not a single uniform forest. Within the wider Amazon region are terra firme forests that are rarely flooded, seasonally flooded forests, riverine forests, wetlands, peatlands, savannas, montane forests and other habitats. Soil chemistry, elevation, flood frequency and drainage strongly influence vegetation. The region therefore contains a mosaic of ecosystems rather than one homogeneous ecological unit. This distinction is important when interpreting statistics about forest area, biodiversity and carbon storage.
Some parts are densely forested and relatively intact, while others have been cleared or degraded. The Amazon biome is broader than the area of dense rainforest, and the Amazon drainage basin is broader still. Using these terms interchangeably can produce misleading comparisons, particularly when calculating area, carbon stocks or rates of deforestation.
The Amazon is larger than the Congo Basin and Southeast Asian tropical forests, making it the largest tropical rainforest, while the Congo Basin is generally recognised as the world's second largest tropical rainforest. WWF estimates that the Congo Basin forests cover around 500 million acres in one current overview, although other assessments use different boundaries and report different areas. Southeast Asia contains another enormous but highly fragmented concentration of tropical forest across numerous countries and islands.
Comparing these regions requires consistent definitions because forest area can be measured using different thresholds and geographical boundaries. The Amazon's distinction as the largest is nevertheless robust across major classification systems. Its immense size, biodiversity, freshwater resources, carbon stocks and influence on regional water cycling make it one of the most consequential ecosystems on Earth.
