Convert measurements between millimetres (mm) and micrometres (μm).

Converting between millimetres (mm) and micrometres (μm)

In biology we often need to switch between the larger scale of millimetres and the tiny scale of micrometres. The key fact is:

$1 \text{ mm} = 1000 \, \mu\text{m}$

So, to convert from mm to μm you multiply by 1000, and to convert from μm to mm you divide by 1000.

1. Write down the number you have.
2. Write the unit (mm or μm).
3. Apply the conversion factor.
4. Write the result with the correct unit.

🔍 Exam tip: Show the conversion factor in your answer. For example, if you convert 0.8 mm to μm, write: 0.8 mm × 1000 μm/mm = 800 μm.

🧪 Analogy: Think of a millimetre as a small stick of chewing gum, and a micrometre as a single hair on that stick. There are 1000 hairs on one stick.

💡 Remember: When you see a number like 0.5 mm, you can think of it as 500 μm because 0.5 × 1000 = 500.

💡 Remember: When you see a number like 300 μm, you can think of it as 0.3 mm because 300 ÷ 1000 = 0.3.

?? Answers:

• 2.5 mm × 1000 = 2500 μm
• 750 μm ÷ 1000 = 0.75 mm
• 0.12 mm × 1000 = 120 μm
• 1200 μm ÷ 1000 = 1.2 mm

❗ Common mistakes: Forgetting to keep the unit symbol (mm or μm) in the final answer, or mixing up the direction of the conversion factor.