# Square centimeters to Square inches (cm² to in²)

> Convert square centimeters to square inches: 1 cm² = 0.155 in². Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

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

## Formula

- `1 cm² = 0.155 in²`
- `square inches = square centimeters × 0.15500031`
- Reverse: `square centimeters = square inches × 6.4516`

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 cm² = 0.775002 in²
- 12.5 cm² = 1.9375 in²
- 100 cm² = 15.5 in²

## Conversion table

| Square centimeters (cm²) | Square inches (in²) |
| --- | --- |
| 1 | 0.155 |
| 2 | 0.310001 |
| 3 | 0.465001 |
| 4 | 0.620001 |
| 5 | 0.775002 |
| 6 | 0.930002 |
| 7 | 1.085 |
| 8 | 1.24 |
| 9 | 1.395 |
| 10 | 1.55 |
| 15 | 2.325 |
| 20 | 3.10001 |
| 25 | 3.87501 |
| 30 | 4.65001 |
| 40 | 6.20001 |
| 50 | 7.75002 |
| 75 | 11.625 |
| 100 | 15.5 |
| 200 | 31.0001 |
| 250 | 38.7501 |
| 500 | 77.5002 |
| 1000 | 155 |

## API

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

1 cm² = 0.155 in². 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 centimeters to square inches?**

Multiply the value in square centimeters by 0.15500031: square inches = square centimeters × 0.15500031. For example, 5 cm² = 0.775002 in².

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

Multiply by the inverse factor 6.4516 (square centimeters = square inches × 6.4516), or use the square inches-to-square centimeters page.

## Related conversions

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