Verification: factors follow standard unit definitions; round for display only.

Square kilometers to square miles

Convert km² to sq mi when a national atlas, geographic database, or international report lists area in square kilometers but you need square miles for US map legends, English-language geography textbooks, or comparative land-area discussions.

Square kilometers and square miles both measure flat area at map and regional scale, but they use different length bases squared. This site anchors area units to the square meter in the shared catalog, where one square kilometer equals 1,000,000 m² and one square mile equals 2,589,988.110336 m². The exact km²-to-sq-mi factor follows directly:

sq mi = km² × 0.386102159  ·  equivalently   sq mi = km² ÷ 2.589988110336

Multiplying by 0.386102159 is preferred when you want the catalog-exact result. Dividing by 2.589988110336 gives the same answer within normal calculator precision.

Step-by-step conversion (worked example 1)

Convert 1 km² to square miles—the exact definition anchor:

1. Write the formula: sq mi = km² × 0.386102159
2. Multiply: 1 × 0.386102159 = 0.386102159 sq mi
3. Round for display: 0.386 sq mi on a map legend
4. Round-trip check: 0.386102159 × 2.589988110336 = 1 km² ✓

Step-by-step conversion (worked example 2)

Convert 100 km² to square miles—a mid-size county or large lake reference:

1. Apply: 100 × 0.386102159 = 38.6102159 sq mi
2. Display: 38.6 sq mi for an English-language geography brief

Step-by-step conversion (worked example 3)

Convert 2,589.988 km² to square miles—approximately one square mile per thousand km² sanity check:

1. Divide: 2,589.988 ÷ 2.589988110336 = 1,000 sq mi (exact ratio check)
2. Anchor: 1 sq mi = 2.589988110336 km²—memorize the inverse for reverse conversions

Quick mental estimate (no calculator)

For a fast approximation, multiply km² by 0.39 instead of 0.386102. Example: 50 km² × 0.39 = 19.5 sq mi (exact: 19.31 sq mi—about 1% high). Some use divide km² by 2.6 for a slightly low estimate. Use 0.386102159 when the value feeds GIS exports or published statistics.

Square kilometer to square mile conversion chart

Where km² → sq mi comes up

• Geography & education: World atlases and CIA World Factbook entries list country areas in km²; US textbooks and English-language journalism often translate to sq mi. France (551,695 km²) → 213,011 sq mi for US readers.
• GIS & mapping: International open-data layers store area in km²; US municipal planning briefs and FEMA-style summaries may expect sq mi. Convert before overlaying watershed or fire-perimeter statistics.
• Conservation & parks: IUCN and UNESCO site listings quote protected area in km²; US NPS comparisons and donor reports sometimes use sq mi. Yellowstone (~8,991 km²) → 3,472 sq mi.
• Real estate at scale: Large ranch or timber holdings in metric countries list km²; US investors comparing to section-based acreage need sq mi or acres via square kilometers to acres.

Square miles to square kilometers

Convert sq mi to km² when a US county atlas, English road map, or imperial land record lists square miles but you need square kilometers for metric GIS, international statistics, or SI environmental reporting.

Reverse the km²-to-sq-mi relationship using the catalog-exact factors. Because 1 sq mi = 2,589,988.110336 m² = 2.589988110336 km², multiply square miles by 2.589988110336 (or divide by 0.386102159).

km² = sq mi × 2.589988110336  ·  equivalently   km² = sq mi ÷ 0.386102159

Step-by-step conversion (worked example)

Convert 1 sq mi to square kilometers—the exact definition anchor:

1. Write the formula: km² = sq mi × 2.589988110336
2. Multiply: 1 × 2.589988110336 = 2.589988110336 km²
3. Round for display: 2.59 km² on a metric map legend
4. Round-trip check: 2.589988110336 × 0.386102159 = 1 sq mi ✓

Quick mental estimate (reverse direction)

Approximation: multiply sq mi by 2.6. Example: 10 sq mi × 2.6 = 26 km² (exact: 25.90 km²—about 0.4% high). Use 2.589988110336 when the value feeds published statistics or GIS attribute tables.

Quick reference (sq mi → km²)

Reverse conversion is essential when you import US Census TIGER area fields (sq mi) into metric watershed models, or when you compare US county sizes to EU NUTS regions in km².

Units compared, common mistakes, and related tools

Both directions share catalog-exact factors derived from the international mile. Avoid shortcut errors, verify with anchor regions, and keep unit symbols explicit on every map legend.

Square kilometers vs square miles at a glance

Why square miles tie to the international mile

One square mile is the area of a square with sides of one international mile (1,609.344 m). Squaring gives 2,589,988.110336 m². Dividing by 1,000,000 m² per km² yields 2.589988110336 km² per sq mi—the same constant behind miles to kilometers because area conversion squares the linear mile factor.

Common mistakes to avoid

• Using 0.39 or 2.6 as exact factors—fine for mental math (~1% error), but use 0.386102159 and 2.589988110336 when comparing country areas or GIS attribute tables.
• Squaring the linear mile factor incorrectly—1 mi = 1.609344 km, but 1 sq mi ≠ 1.609344 km². Area conversion uses 2.589988110336 km² per sq mi, not 1.609344.
• Treating 1 km² as “about 1 sq mi”—1 km² = 0.386 sq mi. A 100 km² park is 38.6 sq mi, not 100 sq mi.
• Confusing square miles with miles of distance—sq mi measures area; mi measures length. A 10 mi road is not 10 sq mi of land.
• Rounding too early on multi-region totals—convert each region at full precision, then sum; per-region rounding skews national area totals.

Exactness and round-trip verification

The factor 0.386102159 is exact given the catalog square-mile definition, not a measured approximation. Converting 100 km² → 38.610 sq mi → 100 km² should recover the original within floating-point limits. Test anchors: 1 km² = 0.386102159 sq mi; 1 sq mi = 2.589988110336 km²; 640 ac = 1 sq mi.

Related area converters

For the inverse of this page, open square miles to square kilometers. For land parcels, see acres to hectares, square meters to square feet, and square kilometers to acres.