Overview

A square kilometre, written km² (or km2), is the area contained within a square whose sides are one kilometre long. It is a derived unit based on the SI unit system and the concept of area. The term appears in both spellings "kilometre" and "kilometer" depending on regional English. The symbol km² is widely used in mapping, statistics and reports to indicate the size of land features, administrative regions and other two‑dimensional extents.

Size and simple definition

Thinking of a square with each side equal to 1,000 metres (one kilometre) gives a direct visual grasp: its interior is one square kilometre. Because the metre is the base SI unit for length, the square kilometre is exactly 1,000,000 square metres. It is convenient for expressing areas larger than a few hectares but smaller than whole countries or continents.

Common conversions

  • 1 km² = 1,000,000 m² (one million square metres)
  • 1 km² = 100 hectares (a hectare = 10,000 m²)
  • 1 km² ≈ 0.3861 square miles (often rounded to 0.39)
  • 1 km² ≈ 247.1 acres (useful for agricultural comparisons)

Uses and examples

Square kilometres are used whenever area is large enough that square metres or hectares become cumbersome. Typical applications include measuring the extent of cities, nature reserves, lakes, agricultural regions and planning zones. In demography and urban studies population density is commonly expressed as inhabitants per km². In environmental science and land management, km² helps compare areas of habitat, watershed extents and land‑use changes over time.

The square kilometre arises naturally from the adoption of the metric system in the late 18th and 19th centuries and from later standardization under the International System of Units. The hectare (100 ares, or 10,000 m²) was adopted earlier by agrarian practice and remains the unit people often use for farms and fields, while the km² is a convenient multiple for larger regions. Different countries and disciplines may prefer one unit over the other for readability.

Distinctions and notable facts

Although the km² is straightforward, care is needed when comparing areas across unit systems: the same numeric value in km² and mi² represent very different extents. Maps and data tables should always state the unit to avoid confusion. For conversion references or further technical definitions see resources on the kilometre and on the metric system. Key practical uses remain population density, land planning and scientific reporting, where a compact, consistent area unit matters for comparison and policy.