Square Inches to Square Millimeters Conversion (sq in to sq mm)

Square Inches to Square Millimeters Converter

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

Results in Square Millimeters:

1 sq in = 645.16 sq mm
1 sq in = 6.4516 sq cm

How to Convert Square Inches to Square Millimeters

To convert a measurement in square inches to a measurement in square millimeters, multiply the area by the following conversion ratio: 645.16 square millimeters/square inch.

Since one square inch is equal to 645.16 square millimeters, you can use this simple formula to convert:

square millimeters = square inches × 645.16

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

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

square millimeters = (5 sq in × 645.16) = 3,225.8 sq mm

conversion scale showing square inches and equivalent square millimeters area values

How Many Square Millimeters Are in a Square Inch?

There are 645.16 square millimeters in a square inch, which is why we use this value in the formula above.

1 sq in = 645.16 sq mm

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

What is a Square Inch?

One square inch is equivalent to the area of a square with sides that are each 1 inch in length. One square inch is equal to 1/144 of a square foot or 1/1,296 of a square yard.

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.

Learn more about square inches.

What is a Square Millimeter?

One square millimeter is equivalent to the area of a square with edges that are each 1 millimeter in length. One square millimeter is equal to 0.00155 square inches or 1/100 of a square centimeter.

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 thousandths, or 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.

Learn more about square millimeters.

Square Inch to Square Millimeter Conversion Table

Table showing various square inch measurements converted to square millimeters.
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

Table showing various square inch measurements converted to square millimeters.

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