# Square Miles to Square km Converter URL: https://speedycalculator.com/calculators/conversion/square-miles-to-square-km/ Last updated: 2026-10-25 > Convert square miles (mi²) to square kilometres (km²): 1 square mile = 2.5899881 km², so multiply by 2.5899881 or divide by 0.38610216. Both fields are editable, so you can also type in square kilometres and get square miles back. ## Inputs - Square miles (mi²) ## Results - Square kilometres ## Formula ``` 1 mi² = 2.5899881 km² 1 km² = 0.38610216 mi² km² = mi² × 2.5899881 ``` ## Explanation One square mile is about 2.59 km². Country and state areas are often given in one and compared in the other. ### How to use the Square Miles to Square km Converter - Type the number of square miles into the **Square miles** field. Decimals such as 0.5 are fine. - Read the answer in **Square kilometres** – it updates as you type, with no button to press. - To convert the other way, type into **Square kilometres** and the square miles are recalculated. - Press **Copy results** to copy both values with the page title, or **Copy link** to share this exact conversion. This page converts only mi² ⇄ km². Need a different unit? Use the general area converter, where you can choose any “from” and “to” unit. ### How it works Both units measure area, so they are always in the same ratio: one square mile equals 2.5899881 square kilometres. The calculator multiplies the number of square miles you type by 2.5899881 to give square kilometres, and when you type into the square kilometres field it divides by the same factor to give square miles. Because the ratio never changes, doubling the square miles always doubles the square kilometres. Results are calculated at full precision and rounded only for display (up to eight decimal places, with very large or small values shown in scientific notation). ### How to convert square miles to square kilometres - Write down the value in square miles, for example **1 mi²**. - Multiply by the conversion factor 2.5899881 (because 1 square mile = 2.5899881 km²). - 1 × 2.5899881 = **2.5899881 km²**. - To go back from square kilometres to square miles, divide by 2.5899881 – or multiply by 0.38610216. ### mi² to km² conversion table Square milesSquare kilometresSquare kilometresSquare miles1 mi²2.5899881 km²1 km²0.38610216 mi²2 mi²5.1799762 km²2 km²0.77220432 mi²5 mi²12.949941 km²5 km²1.9305108 mi²10 mi²25.899881 km²10 km²3.8610216 mi²50 mi²129.49941 km²20 km²7.7220432 mi²100 mi²258.99881 km²50 km²19.305108 mi²1,000 mi²2,589.9881 km²100 km²38.610216 mi²1,000 km²386.10216 mi² ### What is a square mile? A square mile is 640 acres, about 2.59 km². U.S. land surveys divide land into one-square-mile sections, and U.S. state and county areas are given in square miles. ### What is a square kilometre? A square kilometre is a million square metres, or 100 hectares. Areas of cities, countries, lakes and national parks are reported in km². ### Quick mental conversion For a fast estimate, multiply square miles by about **2.6** to get square kilometres; the error is about 0.4%. Use the calculator above when you need the exact figure. ### Common mistakes to avoid Converting area with a length factor (1 m = 3.28 ft, but 1 m² = 10.76 ft², not 3.28 ft²), and assuming regional land units such as marla, bigha or katha have one standard size everywhere. ## Worked example Inputs — Square miles: 1 mi². Results — **Square kilometres = 2.58998811 km²**. ## FAQ **How many km² in a square mile?** About 2.58999 km². **How many square miles is 100 km²?** About 38.61 mi². **How do I convert square miles to square kilometres?** Multiply the number of square miles by 2.5899881. For example, 1 mi² × 2.5899881 = 2.5899881 km². **How do I convert square kilometres back to square miles?** Divide by 2.5899881 (or multiply by 0.38610216), or simply type the value into the square kilometres field above. **What is 10 mi² in square kilometres?** 10 mi² = 25.899881 km². **What is 100 mi² in square kilometres?** 100 mi² = 258.99881 km². **Is this conversion exact?** Yes. The factor comes from the official definitions of both units (NIST and the SI), so the only difference you may see is rounding in the last displayed digit. **Can I convert to other units on this page?** This page converts only between square miles and square kilometres. To pick any area unit, use the general area converter linked under Related calculators. **What formula does the Square Miles to Square km Converter use?** 1 mi² = 2.5899881 km². ## Sources - [NIST Special Publication 811 – Guide for the Use of the International System of Units](https://www.nist.gov/pml/special-publication-811) - [NIST Handbook 44 Appendix C – General tables of units of measurement](https://www.nist.gov/pml/owm/nist-handbook-44-current-edition)