# Square kilometers to Square miles (km² to mi²)

> Convert square kilometers to square miles: 1 km² = 0.386102 mi². Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

- Page id: `square-km-to-square-miles` · Quantity: Area (`area`, base unit m2) · Tool: `convert_units`
- Canonical page: https://tttkmbb.com/conversion/square-km-to-square-miles · This document: https://tttkmbb.com/conversion/square-km-to-square-miles.md · JSON: https://tttkmbb.com/conversion/square-km-to-square-miles.json (add `?value=` for a result)

## Formula

- `1 km² = 0.386102 mi²`
- `square miles = square kilometers × 0.3861021585`
- Reverse: `square kilometers = square miles × 2.58998811`

The factor follows from the SI definitions of both units (NIST SP 811); values below are rounded to 6 significant figures, the API returns up to 12.

## Worked examples

- 5 km² = 1.93051 mi²
- 12.5 km² = 4.82628 mi²
- 100 km² = 38.6102 mi²

## Conversion table

| Square kilometers (km²) | Square miles (mi²) |
| --- | --- |
| 1 | 0.386102 |
| 2 | 0.772204 |
| 3 | 1.15831 |
| 4 | 1.54441 |
| 5 | 1.93051 |
| 6 | 2.31661 |
| 7 | 2.70272 |
| 8 | 3.08882 |
| 9 | 3.47492 |
| 10 | 3.86102 |
| 15 | 5.79153 |
| 20 | 7.72204 |
| 25 | 9.65255 |
| 30 | 11.5831 |
| 40 | 15.4441 |
| 50 | 19.3051 |
| 75 | 28.9577 |
| 100 | 38.6102 |
| 200 | 77.2204 |
| 250 | 96.5255 |
| 500 | 193.051 |
| 1000 | 386.102 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=km2&to_unit=mi2` → unified JSON envelope with `result.values.result`, `formula`, `factor`, `sources`, `freshness`
- MCP: server `https://tttkmbb.com/mcp`, tool `convert_units` with `{"value":5,"from_unit":"km2","to_unit":"mi2"}`
- All area units: https://tttkmbb.com/api/v1/units?quantity=area · full converter: [Area Converter](https://tttkmbb.com/conversion/area.md)
- Authentication: none. Freshness: `static` (fixed conversion factors).

## FAQ

**How many square miles are in one square kilometer?**

1 km² = 0.386102 mi². The factor comes from the SI definitions of both units (NIST SP 811 / BIPM), so it is exact or correct to at least 10 significant figures.

**What is the formula to convert square kilometers to square miles?**

Multiply the value in square kilometers by 0.3861021585: square miles = square kilometers × 0.3861021585. For example, 5 km² = 1.93051 mi².

**How do I convert square miles back to square kilometers?**

Multiply by the inverse factor 2.58998811 (square kilometers = square miles × 2.58998811), or use the square miles-to-square kilometers page.

## Related conversions

- [Square miles to square kilometers](https://tttkmbb.com/conversion/square-miles-to-square-km.md) (reverse)
- [Square meters to Square feet](https://tttkmbb.com/conversion/square-meters-to-square-feet.md)
- [Square feet to Square meters](https://tttkmbb.com/conversion/square-feet-to-square-meters.md)
- [Acres to Hectares](https://tttkmbb.com/conversion/acres-to-hectares.md)
- [Hectares to Acres](https://tttkmbb.com/conversion/hectares-to-acres.md)
- [Acres to Square meters](https://tttkmbb.com/conversion/acres-to-square-meters.md)
- [Square meters to Acres](https://tttkmbb.com/conversion/square-meters-to-acres.md)
- [Hectares to Square meters](https://tttkmbb.com/conversion/hectares-to-square-meters.md)
- [Square meters to Hectares](https://tttkmbb.com/conversion/square-meters-to-hectares.md)

## Data Sources

- NIST Special Publication 811 – Guide for the Use of the International System of Units (SI), Appendix B conversion factors — https://www.nist.gov/pml/special-publication-811 (standard, retrieved 2026-09-24)
- BIPM – The International System of Units (SI Brochure, 9th edition) — https://www.bipm.org/en/publications/si-brochure (standard, retrieved 2026-09-24)
- Wikipedia – Conversion of units — https://en.wikipedia.org/wiki/Conversion_of_units (reference, retrieved 2026-09-24)