Square Millimeter to Square Inch Conversion Calculator: Free Online Tool

Convert square millimeters to square inches with our free online area converter.

From:

mm²

Square Millimeter

To:

in²

Square Inch

How to Use the Calculator:

Enter the value you want to convert in the 'From' field (Square Millimeter).
The converted value in Square Inch will appear automatically in the 'To' field.
Use the dropdown menus to select different units within the Area category.
Click the swap button (⇌) to reverse the conversion direction.

How to Convert Square Millimeter to Square Inch

Converting Square Millimeter to Square Inch involves multiplying the value by a specific conversion factor, as shown in the formula below.

Formula:

1 Square Millimeter = 0.00155 square inches

Example Calculation:

Convert 10 square millimeters: 10 × 0.00155 = 0.0155 square inches

Note: Conversion factors can sometimes be rounded for display purposes. For precise calculations, always use the full factor or rely on the calculator above.

What is a Square Millimeter and a Square Inch?

The square millimeter (symbol: mm²) is a unit of area in the metric system. It represents the area of a square with sides that are each one millimeter long.

The square inch (symbol: in², sq in) is an imperial and US customary unit of area. It represents the area of a square with sides that are each one inch long.

Note: The Square Millimeter is part of the metric (SI) system, primarily used globally in science and trade. The Square Inch belongs to the imperial/US customary system.

History of the Square Millimeter and Square Inch

Derived from the millimeter (one-thousandth of a meter), the square millimeter arose with the metric system as a unit for measuring extremely small areas, particularly in scientific and technical fields requiring high precision.

Derived from the inch, whose definition has varied historically but was standardized as 25.4 mm, the square inch became a common unit for small area measurements within the imperial system. It is frequently used in the US and UK for engineering and everyday measurements.

Common Uses for square millimeters and square inches

Explore the typical applications for both Square Millimeter (metric) and Square Inch (imperial/US) to understand their common contexts.

Common Uses for square millimeters

Engineering & Manufacturing: Specifying tolerances, cross-sectional areas of fine wires or fibers, surface areas of micro-components.
Material Science: Measuring grain sizes, or the area of microscopic features.
Electronics: Defining the area of pads or traces on printed circuit boards (PCBs).
Optics: Measuring the area of small apertures or sensor elements.

Common Uses for square inches

Engineering & Manufacturing (US/UK): Specifying the area of small components, cross-sections, or surface areas.
Material Measurement: Measuring the area of small sheets of material (e.g., paper, fabric samples).
Pressure Measurement: Used implicitly in units like pounds per square inch (psi).
Crafts & Hobbies: Measuring fabric squares, paper sizes, or small design areas.

Frequently Asked Questions

Questions About Square Millimeter (mm²)

How many square millimeters are in a square centimeter?

There are 100 square millimeters in one square centimeter (cm²).

Is mm² used for everyday measurements?

No, it is generally too small for everyday use. Square centimeters (cm²) or square meters (m²) are more practical for common objects.

How does mm² relate to the square meter?

One square meter contains 1,000,000 square millimeters.

Is mm² an SI unit?

It is derived from the SI base unit meter and is a standard metric unit for area.

About Square Inch (in²)

How many square inches are in a square foot?

There are 144 square inches in one square foot (12 inches x 12 inches).

How many square centimeters are in a square inch?

One square inch is equal to exactly 6.4516 square centimeters.

Is the square inch used for large areas?

No, it's used for small areas. Square feet (ft²) or square yards (yd²) are used for room sizes, and acres (ac) or square miles (mi²) for land.

Is the square inch an SI unit?

No, it is part of the imperial and US customary systems. The corresponding metric units are square centimeter (cm²) or square millimeter (mm²).

Conversion Table: Square Millimeter to Square Inch

Square Millimeter (mm²)	Square Inch (in²)
1	0.002
5	0.008
10	0.016
25	0.039
50	0.078
100	0.155
500	0.775
1,000	1.55

All Area Conversions

Square Meter to Square Kilometer Square Meter to Square Centimeter Square Meter to Square Millimeter Square Meter to Square Inch Square Meter to Square Foot Square Meter to Square Yard Square Meter to Square Mile Square Meter to Acre Square Meter to Hectare Square Kilometer to Square Meter Square Kilometer to Square Centimeter Square Kilometer to Square Millimeter Square Kilometer to Square Inch Square Kilometer to Square Foot Square Kilometer to Square Yard Square Kilometer to Square Mile Square Kilometer to Acre Square Kilometer to Hectare Square Centimeter to Square Meter Square Centimeter to Square Kilometer Square Centimeter to Square Millimeter Square Centimeter to Square Inch Square Centimeter to Square Foot Square Centimeter to Square Yard Square Centimeter to Square Mile Square Centimeter to Acre Square Centimeter to Hectare Square Millimeter to Square Meter Square Millimeter to Square Kilometer Square Millimeter to Square Centimeter Square Millimeter to Square Foot Square Millimeter to Square Yard Square Millimeter to Square Mile Square Millimeter to Acre Square Millimeter to Hectare Square Inch to Square Meter Square Inch to Square Kilometer Square Inch to Square Centimeter Square Inch to Square Millimeter Square Inch to Square Foot Square Inch to Square Yard Square Inch to Square Mile Square Inch to Acre Square Inch to Hectare Square Foot to Square Meter Square Foot to Square Kilometer Square Foot to Square Centimeter Square Foot to Square Millimeter Square Foot to Square Inch Square Foot to Square Yard Square Foot to Square Mile Square Foot to Acre Square Foot to Hectare Square Yard to Square Meter Square Yard to Square Kilometer Square Yard to Square Centimeter Square Yard to Square Millimeter Square Yard to Square Inch Square Yard to Square Foot Square Yard to Square Mile Square Yard to Acre Square Yard to Hectare Square Mile to Square Meter Square Mile to Square Kilometer Square Mile to Square Centimeter Square Mile to Square Millimeter Square Mile to Square Inch Square Mile to Square Foot Square Mile to Square Yard Square Mile to Acre Square Mile to Hectare Acre to Square Meter Acre to Square Kilometer Acre to Square Centimeter Acre to Square Millimeter Acre to Square Inch Acre to Square Foot Acre to Square Yard Acre to Square Mile Acre to Hectare Hectare to Square Meter Hectare to Square Kilometer Hectare to Square Centimeter Hectare to Square Millimeter Hectare to Square Inch Hectare to Square Foot Hectare to Square Yard Hectare to Square Mile Hectare to Acre