The millimeter (mm) is a unit of length in the International System of Units (SI), defined as one thousandth of a meter. This means:

• 1 millimeter = 0.001 meters
• There are 1000 millimeters in one meter
• 1 millimeter equals 1000 micrometers or 1,000,000 nanometers
• In the imperial system, 1 millimeter is exactly 0.03937 inches (about 5/127 of an inch)

Millimeters are commonly used to measure small lengths or thicknesses, such as in engineering, manufacturing, and everyday measurements

. For a practical sense of size:

• 1 mm is roughly the thickness of a credit card
• 10 mm equals 1 centimeter
• 25 mm is about 1 inch

Conversion examples:

• 1 mm ≈ 0.039 inch
• 5 mm ≈ 3/16 inch
• 10 mm ≈ 3/8 inch

Thus, a millimeter is a very small unit of length, suitable for precise measurements of small objects or distances