What Is the Largest Desert in the World?

Quick Orientation: What Counts as a “Desert”

Geographers define a desert by aridity, typically where annual precipitation averages below about 250 millimeters (10 inches). Some authorities extend the upper limit toward 300 mm (12 inches), and call 250–400 mm “semidesert.” In practice, classification can vary by method and region.

That’s why deserts need not be hot or sandy. Polar regions with scant snowfall and extremely low moisture are also deserts. The Antarctic interior receives <50 mm (2 inches) a year—drier than many dune fields. The definition hinges on water balance, not temperature. For consistency, this article follows major reference sources that recognize polar deserts alongside hot deserts.

Why Cold, Icy Places Can Be Deserts

In polar deserts, air is so cold and stable that it holds little moisture. Snow that does fall tends to sublimate or compact into ice; liquid water for plants is rare. Life persists—but sparingly—in microbial mats, hardy lichens, and specialized invertebrates adapted to freeze–thaw cycles.

For readers who want a deeper dive into the definition, NASA’s Earth Observatory overview of desert biomes offers a clear, classroom-grade explanation; Britannica’s survey of the world’s largest deserts provides the standard reference areas.

Largest Deserts by Area (Top 10)

Below is a concise comparison of the world’s ten largest deserts (grouping both polar and hot types). Areas are rounded and compiled from Encyclopaedia Britannica’s curated list; values vary slightly across sources due to shifting boundaries and measurement approaches.

Notice the top two are polar deserts. If the question specifically asks for the largest hot desert, the title goes to the Sahara. For a general “largest desert” without qualifiers, the answer is Antarctica—by a wide margin.

Antarctic vs. Sahara: “Largest Desert” vs. “Largest Hot Desert”

The Sahara spans roughly 8.6 million km² (3.32 million sq mi) using conservative boundaries, stretching about 3,000 miles (4,800 kilometers) east–west across North Africa. Some educational and media sources quote around 9.0 million km² (3.5 million sq mi); both figures appear in reputable references and reflect the difficulty of drawing crisp edges in transitional zones.

By comparison, the Antarctic Desert covers approximately 13.96 million km² (5.39 million sq mi), with its interior receiving less than 50 mm (2 inches) of precipitation annually. On the coast, totals are still desert-low, often around 200 mm (7.9 inches). That combination of extreme cold and extreme dryness is what makes Antarctica the world’s largest desert overall.

Why Estimates Differ

Desert size can change with climate cycles and measurement choices. Researchers may include or exclude fringe semidesert belts; use different precipitation cutoffs (250 mm vs. 300 mm); or revise totals as better satellite data emerge. That’s why you’ll see the Sahara reported in a range and the Antarctic given to the nearest hundreds of thousands.

How Deserts Form: The Simple Science

Most deserts sit beneath the descending limbs of the Hadley cell near 30° N/S, where sinking air warms and dries out, suppressing clouds and rain. Others form in the rain shadow of mountains (air loses moisture while rising, then dries as it descends), or along cold currents where chilled air limits evaporation and convection.

Polar deserts operate differently: there, cold, stable air can’t hold much moisture, so snowfall is scant. Even when snow falls, liquid water is scarce because temperatures stay below freezing. These mechanisms—subtropical highs, orographic rain shadows, cold currents, and polar stability—explain why deserts appear on western continental margins, deep interiors, and at Earth’s frozen ends. For an accessible primer, see Britannica’s explainer How Do Deserts Form?.

Where You’ll Find Them on the Map

Hot deserts cluster along the “horse latitudes” (roughly 15°–35° from the Equator). The Sahara, Arabian, and Australian deserts fit this belt, as do North America’s Great Basin and Sonoran. Cold mid-latitude deserts occupy continental interiors, like the Gobi. Polar deserts dominate the Antarctic and Arctic, which together span over 27 million km² (10.4 million sq mi).

To visualize scale: the Sahara’s east-to-west span of about 3,000 miles (4,800 kilometers) is roughly the distance from New York to Los Angeles. Antarctica’s area exceeds that of the United States and Mexico combined. These comparisons underscore why “largest desert” depends on whether we include polar deserts—which modern references generally do.

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