Square Kilometers to Square Miles Converter — Convert km² to mi² (Exact: 1 mi² = 2.589988110336 km²)
Accurate square kilometers (km²) to square miles (mi²) converter using exact definitions: 1 mile = 1609.344 m ⇒ 1 square mile = 2.589988110336 km². Built for geography, GIS, conservation reporting, logistics coverage areas, and market size analysis. Includes exact formulas, step-by-step examples, expanded reference tables, and an in-depth FAQ.
Exact bases: 1 mi = 1609.344 m ⇒ 1 mi² = 2.589988110336 km². Therefore mi² = km² ÷ 2.589988110336 (≈ km² × 0.386102158542). See all free area converters.
About Square Kilometers to Square Miles Conversion
The square kilometer (km²) is the SI-based unit widely used by GIS teams, researchers, conservation groups, and national statistics offices. The square mile (mi²) remains common in US media, transportation planning, and legacy datasets. Converting km² to mi² helps you present the same underlying area in whichever unit your audience expects—without losing precision.
Because the international mile is fixed exactly at 1609.344 meters, the square-mile constant is exact too: 1 mi² = 2.589988110336 km². That means if you store areas in a single canonical unit (often km² for SI workflows) and convert on demand, you’ll get consistent results across maps, dashboards, PDFs, and CSV exports—as long as you round once at display time.
A dependable approach is to store area_km2 in your database, derive area_mi2 for US-facing front-ends, and document your constants and rounding policy in a short “Methods” note shared across teams.
Square Kilometers to Square Miles Formula
Exact relationship
Use either expression:
mi² = km² ÷ 2.589988110336
// or
mi² ≈ km² × 0.386102158542Example:
100 km² ÷ 2.589988110336 = 38.6102158542 mi²Related Area Converters
What is a Square Kilometer (km²)?
One square kilometer is the area of a square with 1-kilometer sides (1000 m × 1000 m). It’s convenient for city neighborhoods, protected areas, watersheds, and market coverage zones. Because it’s built on SI units, it composes naturally with other metrics and GIS layers.
What is a Square Mile (mi²)?
A square mile is the area of a square with 1-mile sides. With the modern mile definition (exactly 1609.344 m), 1 mi² = 2.589988110336 km² exactly. It’s widely used in US demographics, transportation planning, and media summaries, and often reported alongside km² in scientific contexts.
Step-by-Step: Converting km² to mi²
- Read the area in square kilometers (km²) from your GIS attribute, table, or report.
- Divide by 2.589988110336 to convert to square miles (mi²).
- Round once at presentation time (e.g., 2–3 decimals for reports; more if your polygons are tiny).
Example walkthrough:
Input: 12.7 km²
Compute: 12.7 ÷ 2.589988110336 = 4.904497… mi²
Output: 4.9045 mi² (UI, 4 decimals)Common Conversions
Quick checks (km² → mi²)
| km² | mi² | km² | mi² |
|---|---|---|---|
| 1 | 0.386102158542 | 5 | 1.93051079271 |
| 10 | 3.86102158542 | 25 | 9.65255396356 |
| 50 | 19.3051079271 | 100 | 38.6102158542 |
| 250 | 96.5255396356 | 1000 | 386.102158542 |
Quick Reference Table
Square miles to square kilometers (mi² → km²)
| mi² | km² | mi² | km² |
|---|---|---|---|
| 1 | 2.589988110336 | 5 | 12.94994055168 |
| 10 | 25.89988110336 | 25 | 64.7497027584 |
| 50 | 129.4994055168 | 100 | 258.9988110336 |
| 250 | 647.497027584 | 1000 | 2589.988110336 |
Precision, Rounding & Significant Figures
Operational rounding
For newsrooms and public dashboards, 2–3 decimals are usually enough. For scientific analysis and compliance, keep additional precision consistent with your spatial data. Always round once at output and keep internal values exact.
Consistent documentation
Name fields clearly (e.g., area_km2, area_mi2) and add a short methods note: “Exact constants: 1 mi² = 2.589988110336 km²; inverse 1 km² ≈ 0.386102158542 mi². Round once at presentation.” This keeps maps, APIs, and exports aligned across teams.
Where This Converter Is Used
- 🗺️ GIS & cartography: Report polygon areas to audiences that expect mi² while you store km².
- 🌿 Conservation & ecology: Habitat extents, protected areas, and wildfire footprints.
- 🏙️ Urban planning: Neighborhoods, districts, and service-area coverage comparisons.
- 🚚 Logistics & ops: Delivery coverage, warehouse catchments, and market territories.
- 📰 Media & education: Easy-to-read summaries that pair mi² headlines with km² source data.
Frequently Asked Questions
What is the exact formula to convert square kilometers to square miles?
Start from exact bases: 1 mile = 1609.344 meters. Therefore 1 mi² = (1609.344 m)² = 2,589,988.110336 m² = 2.589988110336 km². To convert km² → mi², divide by 2.589988110336 (or multiply by ≈ 0.386102158542). The reverse is km² = mi² × 2.589988110336. These constants are exact, so your results are reproducible across GIS, spreadsheets, and reports.
Why do area conversions square the length factor?
Area is two-dimensional. A length conversion (km ↔ mi) must be squared for area. Since 1 km ≈ 0.621371192237 mi, squaring gives 1 km² ≈ 0.386102158542 mi². Forgetting to square is a common mistake that underestimates or overestimates areas by a factor of ~1.62 instead of ~0.386.
How should I round km² ↔ mi² for dashboards, papers, and press releases?
Keep full precision internally and round once at presentation. For press and marketing, 2–3 decimals in mi² or km² is readable. For scientific and GIS outputs, carry enough decimals to match your source data resolution (e.g., to 0.0001 km²). Publish your rounding policy so maps, PDFs, and CSVs stay consistent.
Does map projection or geodesy change the unit conversion?
The unit conversion is fixed and independent of projection. However, measuring area on the Earth’s surface depends on your geodesic method and projection (planar vs. geodesic area). Compute the area correctly for your geometry first, then apply the same km² ↔ mi² conversion.
Can I mix km² and mi² values in the same column and sum them?
Avoid mixing units in one field. Normalize to a canonical unit (many teams choose km²), perform all math and aggregations, then convert for UI. Mixed-unit columns are a frequent source of audit discrepancies and off-by-percent errors.
What precision do I need for small polygons vs. very large regions?
Use more decimals for small features (urban parcels, reserves) and fewer for very large regions (states, basins). As a rule of thumb: retain at least one extra decimal beyond your data’s spatial resolution and round once at presentation.
How can I validate my km² ↔ mi² pipeline automatically?
Maintain regression pairs—e.g., 1 km² = 0.386102158542 mi²; 100 km² = 38.6102158542 mi²; 1 mi² = 2.589988110336 km²—and assert both directions in CI. This catches accidental constant edits and double-rounding issues early.