Square Kilometer (km²) - Unit Information & Conversion

Definition

The Square Kilometer (symbol: km² or sq km) is a multiple of the square meter (m²), the base unit of area in the International System of Units (SI). It represents the area of a square whose sides measure exactly one kilometer (km) in length.

Key relationships:

• 1 km² = 1 kilometer × 1 kilometer
• 1 km = 1,000 meters (m)
• Therefore, 1 km² = (1,000 m) × (1,000 m) = 1,000,000 square meters (m²)
• 1 km² = 100 hectares (ha) (since 1 hectare = 10,000 m²)

In terms of imperial/US customary units:

• 1 km² ≈ 0.3861 square miles (mi²)
• 1 km² ≈ 247.1 acres (ac)

History

• Origin: The square kilometer is derived directly from the kilometer, a unit of length introduced as part of the metric system, which was developed in France during the late 18th century.
• Metric System Adoption: The metric system, including the meter and its multiples like the kilometer, was created to provide a standardized, decimal-based system of measurement. As nations began adopting the metric system throughout the 19th and 20th centuries, the square kilometer naturally became the standard unit for expressing large geographical areas.
• SI Standard: The International System of Units (SI), formally established in 1960, confirmed the square meter (m²) as the base unit of area. The square kilometer is a widely accepted and commonly used multiple of this base unit, consistent with SI prefixes.
• Global Usage: Today, the square kilometer is the predominant unit used worldwide for measuring the land area of countries, large administrative regions, bodies of water, and other significant geographical features.

Common Uses

The square kilometer is almost exclusively used for measuring large-scale areas:

• Geography and Cartography: The standard unit for stating the land or surface area of countries, continents, large islands, administrative divisions (states, provinces), and major cities.
• Demography: Essential for calculating population density, typically expressed as inhabitants per square kilometer (people/km²).
• Environmental Science: Measuring the extent of large ecosystems (forests, deserts, wetlands), national parks, conservation areas, watersheds, ice sheets, or the area impacted by large-scale environmental events (e.g., oil spills, deforestation).
• Urban Planning and Land Management: Quantifying large zones, districts, or total city area in regional planning.
• Geology and Planetary Science: Measuring the surface area of large geological formations or the surface areas of planets, moons, and asteroids.
• Military and Logistics: Defining large operational areas or zones.

It is too large for measuring individual properties, farms (hectares or acres are preferred), or room sizes (square meters or square feet are used).

Unit FAQs

How many square meters are in one square kilometer?

There are exactly 1,000,000 square meters (m²) in one square kilometer. This is calculated as 1,000 meters × 1,000 meters.

How many hectares are in one square kilometer?

There are exactly 100 hectares (ha) in one square kilometer. (1 km² = 1,000,000 m² and 1 ha = 10,000 m²).

How do you convert square kilometers to square miles?

To convert square kilometers to square miles, multiply the area in square kilometers by approximately 0.386102.

• Conversion formula: Area [mi²] ≈ Area [km²] × 0.386102
• Example: 100 km² ≈ 100 × 0.386102 mi² ≈ 38.61 mi²

Conversely, to convert square miles to square kilometers, multiply by approximately 2.58999.

• 1 mi² ≈ 2.59 km²

Is the square kilometer an official SI unit?

Strictly speaking, the official SI derived unit for area is the square meter (m²). However, the square kilometer (km²) is formed by combining an SI prefix (kilo-) with the SI base unit (meter) raised to the power of two, making it a standard and fully accepted multiple within the metric system and for use alongside SI units.

What is the difference between a kilometer and a square kilometer?

A kilometer (km) is a unit of length or distance (one dimension). A square kilometer (km²) is a unit of area (two dimensions), representing a square with sides of one kilometer each.