sq mi to sq km Converter
Convert square miles to square kilometers for maps and land areas
Square miles to square kilometers FAQ
How do you convert square miles to square kilometers exactly?
The calculator uses the relationship where 1 square mile = 2.589988110336 square kilometers. That comes from the exact definition of the mile as 1609.344 meters and then squaring that length. To convert from sq mi to sq km, you multiply the area in square miles by 2.589988110336. For example, 50 sq mi becomes about 129.50 sq km. The tool applies this precise factor and handles the rounding so you can copy results straight into maps, tables or reports.
Why do some atlases or sites show slightly different values?
Some printed atlases, textbooks or online tools use rounded factors such as 2.59 or 2.6 instead of 2.589988110336. Over small areas the difference is tiny, but when you convert large regions, you may see a few square kilometers of variation. This converter keeps the full precision of the square mile to square kilometer factor, then rounds the display, giving you consistent numbers whenever you revisit the same areas.
What’s 100 square miles in square kilometers?
Using the exact factor, 100 sq mi ≈ 258.999 sq km, which is often rounded to 259 sq km in narrative descriptions. Likewise, 10 sq mi is about 25.90 sq km, 250 sq mi is about 647.50 sq km, and 1000 sq mi comes out close to 2589.99 sq km. The converter produces these same values without you needing to remember any of the intermediate steps.
Is a square mile bigger than a square kilometer?
Yes. A square mile is larger than a square kilometer. Since one square mile equals about 2.59 sq km, a region described as 10,000 sq mi covers roughly 25,900 sq km. This converter keeps the actual area constant and just expresses it in whichever unit a dataset, policy document or audience expects.
Can I use this for country sizes, states and protected areas?
Absolutely. The sq mi to sq km converter is built for geography, environmental science, policy briefs and news articles. You might have a country or state area given in square miles but need to compare it with data expressed in square kilometers, or vice versa. Type the official sq mi figure from your source and paste the sq km result into GIS notes, fact sheets, dashboards, presentations or articles.
Is there a quick mental shortcut for sq mi to sq km?
A helpful rule of thumb is to multiply by 2.6 and then subtract about 0.5 %. For example, 40 sq mi → 40 × 2.6 = 104, minus a small amount gives roughly 104 sq km, which is close to the exact 103.60 sq km. Another rough check is to multiply by 3 and then subtract about 13 %. The calculator always uses the precise 2.589988110336 factor, so you can use mental shortcuts just to sanity-check the order of magnitude.
From imperial land areas to clean metric numbers
This sq mi to sq km converter is built for situations where your land areas are given in square miles but you need to analyze or present them in square kilometers. That is common when you combine U.S. or U.K. data with international sources, compare national parks across countries, or work with climate, biodiversity or population datasets from different agencies. Instead of re-building formulas in a spreadsheet each time, you enter the square miles, tap convert, and get a neat line such as “120 sq mi = 310.80 sq km”.
1. Simple single-box interface for regions of any size
The interface stays minimal: a single box for square miles and a result card underneath. It works the same way whether you are converting a local watershed, a county, a protected habitat or an entire state. Decimals are supported, so areas like 12.5 sq mi for a small reserve or 1234.75 sq mi for a mixed-use region convert accurately. Behind the scenes, the converter applies the exact factor based on the defined mile and kilometer and formats the output for quick copying into your notes, maps and documents.
When you need to flip the direction, the “Swap Units” button takes you straight to the sq km to sq mi page. That way you can move back and forth between imperial and metric land areas without adjusting a more complex multi-unit tool or hunting for another calculator.
2. Exact relationship: 1 sq mi = 2.589988110336 sq km
The converter is grounded in the exact definition of the mile: 1 mile = 1609.344 meters. Squaring that length gives an area of 2,589,988.110336 square meters, which equals 2.589988110336 square kilometers. That fixed relationship is used in surveying, cartography, environmental impact assessments and official statistics. By using the same factor, the tool keeps your conversions aligned with those professional standards and avoids small inconsistencies across different projects.
If you need to jump between other units like hectares, acres or square meters, you can move up to the full area conversion calculator. It keeps the same clean style of results while handling many more unit pairs in one place.
3. Common sq mi to sq km values at a glance
Here are some quick reference points that match what the calculator produces. They help you build intuition for how big different square-mile values are in the metric system:
| Square miles (sq mi) | Square kilometers (sq km) |
|---|---|
| 1 sq mi | 2.59 sq km |
| 5 sq mi | 12.95 sq km |
| 10 sq mi | 25.90 sq km |
| 20 sq mi | 51.80 sq km |
| 50 sq mi | 129.50 sq km |
| 100 sq mi | 259.00 sq km |
| 250 sq mi | 647.50 sq km |
| 500 sq mi | 1294.99 sq km |
| 1000 sq mi | 2589.99 sq km |
A quick mental check is to multiply by 2.5 and then add about 4 % of the original number. For example, 200 sq mi → 200 × 2.5 = 500, plus an extra 8 gives roughly 508 sq km, which is close to the more exact 517.99 sq km. The converter hides the detailed factor and simply presents the final precise figure whenever you need it.
4. Where the sq mi to sq km converter shines
You will most often reach for this tool when you:
- Compare countries and states — convert square-mile figures in factbooks into square kilometers for international comparisons.
- Work with environmental and conservation data — match protected area sizes, habitat extents and watershed areas to metric datasets.
- Prepare maps and educational material — convert textbook or atlas areas so charts and activities can use a single unit system.
- Write articles and reports — translate official sq mi statistics into sq km for audiences used to metric units.
- Align mixed-unit datasets — standardize square-mile data before loading it into GIS tools, dashboards or analytical pipelines.
Because the underlying conversion is fixed by international definitions, this square miles to square kilometers converter gives the same answer every time for a given input. It becomes a dependable reference as you move between raw datasets, maps, models and narrative explanations that mix imperial and metric area measurements.
References and further reading on sq mi and sq km
These references explain how square miles and square kilometers are defined and used:
- Square mile — describes the square mile as an imperial and U.S. customary unit of area and its relationship to metric units.
- Square kilometre — covers the square kilometer as a metric unit commonly used for regions, cities and countries.
- SI Units — Area (NIST) — provides background on square meters, related SI area units and how they underpin conversions to and from imperial units.
For legal documents, official statistics or regulated reporting, always follow your jurisdiction’s measurement standards and rounding rules when converting between sq mi and sq km.