# Square Inches to Square Millimeters Conversion

Enter the area in square inches below to get the value converted to square millimeters.

**Results in Square Millimeters:**

## How to Convert Square Inches to Square Millimeters

To convert a square inch measurement to a square millimeter measurement, multiply the area by the conversion ratio. One square inch is equal to 645.16 square millimeters, so use this simple formula to convert:

The area in square millimeters is equal to the square inches multiplied by 645.16.

**For example,**here's how to convert 5 square inches to square millimeters using the formula above.

Square inches and square millimeters are both units used to measure area. Keep reading to learn more about each unit of measure.

## Square Inches

One square inch is equal to the area of a square with sides that are 1 inch in length.

The square inch is a US customary and imperial unit of area. A square inch is sometimes also referred to as a square in. Square inches can be abbreviated as *sq in*, and are also sometimes abbreviated as *in²*. For example, 1 square inch can be written as 1 sq in or 1 in².

## Square Millimeters

One square millimeter is equal to the area of a square with edges that are 1 millimeter in length.

The square millimeter, or square millimetre, is a multiple of the square meter, which is the SI derived unit for area. In the metric system, "milli" is the prefix for 10^{-3}. A square millimeter is sometimes also referred to as a square mm. Square millimeters can be abbreviated as *sq mm*, and are also sometimes abbreviated as *mm²*. For example, 1 square millimeter can be written as 1 sq mm or 1 mm².

## Square Inch to Square Millimeter Conversion Table

Square Inches | Square Millimeters |
---|---|

1 sq in | 645.16 sq mm |

2 sq in | 1,290 sq mm |

3 sq in | 1,935 sq mm |

4 sq in | 2,581 sq mm |

5 sq in | 3,226 sq mm |

6 sq in | 3,871 sq mm |

7 sq in | 4,516 sq mm |

8 sq in | 5,161 sq mm |

9 sq in | 5,806 sq mm |

10 sq in | 6,452 sq mm |

11 sq in | 7,097 sq mm |

12 sq in | 7,742 sq mm |

13 sq in | 8,387 sq mm |

14 sq in | 9,032 sq mm |

15 sq in | 9,677 sq mm |

16 sq in | 10,323 sq mm |

17 sq in | 10,968 sq mm |

18 sq in | 11,613 sq mm |

19 sq in | 12,258 sq mm |

20 sq in | 12,903 sq mm |

21 sq in | 13,548 sq mm |

22 sq in | 14,194 sq mm |

23 sq in | 14,839 sq mm |

24 sq in | 15,484 sq mm |

25 sq in | 16,129 sq mm |

26 sq in | 16,774 sq mm |

27 sq in | 17,419 sq mm |

28 sq in | 18,064 sq mm |

29 sq in | 18,710 sq mm |

30 sq in | 19,355 sq mm |

31 sq in | 20,000 sq mm |

32 sq in | 20,645 sq mm |

33 sq in | 21,290 sq mm |

34 sq in | 21,935 sq mm |

35 sq in | 22,581 sq mm |

36 sq in | 23,226 sq mm |

37 sq in | 23,871 sq mm |

38 sq in | 24,516 sq mm |

39 sq in | 25,161 sq mm |

40 sq in | 25,806 sq mm |