Millimetre facts for kids

The millimetre (symbol: mm) is a very small unit of length. It's part of the Metric system, which is used by most countries around the world for measuring things. The millimetre helps us measure tiny objects and distances with great accuracy.

There are 1,000 millimetres in one metre. To give you an idea, a metre is about the length of a large step or a guitar. So, a millimetre is one thousandth of that!

What is a Millimetre?

A millimetre is a unit of length, just like a centimetre, a metre, or a kilometre. It's the smallest common unit you'll find on a standard ruler.

• How small is it? Imagine a regular ruler. The smallest lines on it usually mark millimetres.
• Part of the metric system: The metric system is based on powers of 10, which makes it easy to convert between units. For example, 10 millimetres make 1 centimetre, and 100 centimetres make 1 metre.

Why Do We Use Millimetres?

Millimetres are super important for measuring things that need to be very precise. When you're building something, designing a circuit, or even making clothes, small differences can matter a lot.

• Accuracy in building: Architects and builders use millimetres to make sure buildings are constructed exactly right. A few millimetres off can cause big problems!
• Engineering and design: When engineers design parts for cars, phones, or even robots, they measure everything in millimetres. This ensures all the pieces fit together perfectly.
• Science and medicine: Scientists use millimetres to measure tiny specimens under microscopes. Doctors might use them to measure small changes in a patient's body.
• Everyday objects: The thickness of a credit card, the diameter of a pencil lead, or the size of a small insect are often best described in millimetres.

Measuring with Millimetres

You can find millimetres on most rulers, tape measures, and even digital calipers.

• Rulers: Look closely at a ruler. Between each centimetre mark, there are usually 10 smaller lines. Each of these small lines represents one millimetre.
• Tape measures: These are used for longer measurements, but they also show millimetres, especially for precise work like carpentry.
• Digital calipers: These are tools that can measure very small distances with extreme accuracy, often down to fractions of a millimetre. They are common in workshops and labs.

Millimetres in Real Life

Here are some examples of things that are commonly measured in millimetres:

• The thickness of a single sheet of paper is about 0.1 millimetres.
• The diameter of a standard pencil lead is usually 0.5 or 0.7 millimetres.
• A typical raindrop can be a few millimetres wide.
• The size of a small ant is often around 2 to 5 millimetres.
• The width of a standard USB-A connector is about 12 millimetres.

Using millimetres helps us be very exact when we need to be, making sure everything from tiny computer chips to large buildings is made just right.

See also

• In Spanish: Milímetro para niños

Images for kids

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  A robot, which might have parts measured in millimetres.