# Square inches to Square centimeters (in² to cm²)

> Convert square inches to square centimeters: 1 in² = 6.4516 cm². Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

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

## Formula

- `1 in² = 6.4516 cm²`
- `square centimeters = square inches × 6.4516`
- Reverse: `square inches = square centimeters × 0.15500031`

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 in² = 32.258 cm²
- 12.5 in² = 80.645 cm²
- 100 in² = 645.16 cm²

## Conversion table

| Square inches (in²) | Square centimeters (cm²) |
| --- | --- |
| 1 | 6.4516 |
| 2 | 12.9032 |
| 3 | 19.3548 |
| 4 | 25.8064 |
| 5 | 32.258 |
| 6 | 38.7096 |
| 7 | 45.1612 |
| 8 | 51.6128 |
| 9 | 58.0644 |
| 10 | 64.516 |
| 15 | 96.774 |
| 20 | 129.032 |
| 25 | 161.29 |
| 30 | 193.548 |
| 40 | 258.064 |
| 50 | 322.58 |
| 75 | 483.87 |
| 100 | 645.16 |
| 200 | 1290.32 |
| 250 | 1612.9 |
| 500 | 3225.8 |
| 1000 | 6451.6 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=in2&to_unit=cm2` → 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":"in2","to_unit":"cm2"}`
- 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 centimeters are in one square inch?**

1 in² = 6.4516 cm². 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 inches to square centimeters?**

Multiply the value in square inches by 6.4516: square centimeters = square inches × 6.4516. For example, 5 in² = 32.258 cm².

**How do I convert square centimeters back to square inches?**

Multiply by the inverse factor 0.15500031 (square inches = square centimeters × 0.15500031), or use the square centimeters-to-square inches page.

## Related conversions

- [Square centimeters to square inches](https://tttkmbb.com/conversion/square-cm-to-square-inches.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)
- [Square kilometers to Square miles](https://tttkmbb.com/conversion/square-km-to-square-miles.md)
- [Square miles to Square kilometers](https://tttkmbb.com/conversion/square-miles-to-square-km.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)