How big is Lake Superior?

Lake Superior is not only the largest of the five Great Lakes of North America but also holds the title of the largest freshwater lake in the world by surface area. Its immense size, both in breadth and depth, makes it a geographical marvel and a powerful natural force that has shaped the surrounding region’s climate, ecosystem, and human activity for centuries.

Surface Area and Dimensions

Lake Superior spans an astonishing 31,700 square miles (82,100 square kilometers) in surface area. To put this into perspective, it is larger than the entire state of South Carolina or roughly the same size as the country of Austria. Lake Superior holds about 10% of the world’s surface fresh water, making it an indispensable global freshwater resource.

The lake stretches approximately:

• 350 miles (563 kilometers) from west to east,
• 160 miles (257 kilometers) from north to south at its widest point.

This vast body of water touches three U.S. states—Minnesota, Wisconsin, and Michigan—as well as the Canadian province of Ontario.

Depth and Volume

In terms of depth, Lake Superior is also extraordinary. It is the deepest of the Great Lakes, with an average depth of 483 feet (147 meters). Its maximum depth is a staggering 1,333 feet (406 meters), located about 40 miles north of Munising, Michigan. This places the lake bed roughly 733 feet (223 meters) below sea level, even though the lake’s surface sits 602 feet (183 meters) above sea level.

Lake Superior contains about 2,900 cubic miles (12,100 cubic kilometers) of water. That’s 3 quadrillion gallons (11.4 quadrillion liters)—enough to cover the entire continents of North and South America with one foot of water.

Coastline and Islands

The shoreline of Lake Superior is equally impressive. The total length of the lake’s shoreline, including its many bays and islands, is approximately 2,726 miles (4,387 kilometers). That’s longer than the distance between New York City and Los Angeles.

The lake contains several large islands, the biggest of which is Isle Royale, located in the northwestern section. Isle Royale, a part of Michigan, is the largest island in Lake Superior and itself contains dozens of inland lakes.

Comparisons with Other Great Lakes

Lake Superior’s size is often best understood when compared with its fellow Great Lakes:

• Lake Michigan: 22,400 sq mi (58,000 km²)
• Lake Huron: 23,000 sq mi (59,600 km²)
• Lake Erie: 9,910 sq mi (25,700 km²)
• Lake Ontario: 7,340 sq mi (19,000 km²)

Lake Superior is almost as large as Lake Michigan and Lake Huron combined and is nearly four times larger than Lake Ontario.

It also ranks as the third-largest lake in the world by volume, trailing only Lake Baikal in Russia and Lake Tanganyika in Africa.

Geological Origins

Lake Superior was formed during the last Ice Age, roughly 10,000 years ago, when retreating glaciers carved out the vast basin that would later be filled with meltwater. The result is a massive freshwater body surrounded by ancient, hard bedrock of the Canadian Shield—making it one of the oldest and most geologically stable regions on Earth.

The depth and shape of the lake basin are a direct result of glacial erosion, which also contributes to its cold water temperatures and the clarity of its water.

Climate Influence

Lake Superior’s immense size also has a noticeable impact on the regional climate. It creates a lake effect that moderates temperatures along the shorelines—cooling them in summer and warming them in winter. It also plays a major role in generating lake-effect snow, especially on the southern and eastern shores, where cold air masses absorb moisture from the lake and deposit heavy snow inland.

Because of its large volume and depth, Lake Superior warms slowly and cools slowly, which is one reason the lake remains so cold even in the peak of summer.

Navigation and Shipping

Lake Superior is a critical part of the Great Lakes–St. Lawrence Seaway, which allows cargo ships to travel from the interior of North America to the Atlantic Ocean. Large freighters carry iron ore, coal, grain, and other bulk materials from ports such as Duluth (Minnesota), Thunder Bay (Ontario), and Marquette (Michigan).

Despite its usefulness, navigation on the lake can be dangerous due to sudden storms, fog, and the lake’s sheer size. Some parts of the lake can feel more like an ocean than an inland water body.

Conclusion

Lake Superior lives up to its name in every respect. Its vast surface area, great depth, and immense water volume make it a dominant force among the Great Lakes and one of the most remarkable freshwater lakes on the planet. Whether you're standing on its rocky shores, sailing across its cold waves, or exploring its deep history, the scale of Lake Superior leaves a lasting impression. It’s not just a lake—it’s a freshwater sea with a grandeur all its own.