How do I convert mL into µL, and vice versa?

When students learn the metric system, they usually learn six main prefixes denoting different units of measurement. For liters, those measurements, from large to small, are as follows:
  • kiloliter (kL): 1,000 liters
  • hectoliter (hL): 100 liters
  • decaliter (daL): 10 liters
  • Of course, sandwiched in here is the plain old liter (L).
  • deciliter (dL): 1/10 of a liter (or 10–1 liters)
  • centiliter (cL): 1/100 of a liter (or 10–2 liters)
  • milliliter (mL): 1/1,000 of a liter (or 10–3 liters)

But the liter can be broken down into much smaller (or much larger) parts than just these seven. And that's where the microliter (µL) comes in. The microliter is 1/1,000,000 of a liter, or 10–6 liters. In other words, a microliter is to the milliliter what the milliliter is to the liter.

In the metric system, converting from one unit of measure to another is simply a matter of moving the decimal point the right number of places. So, to convert 7L into milliliters (10–3 liters), you move the decimal point 3 places to the right:

7L = 7,000 mL

To convert this into µL, move the decimal three more places to the right:

7L = 7,000mL = 7,000,000µL

To convert units in the other direction, you move the decimal point in the other direction. So, to convert 4,500µL into milliliters, move the decimal point three places to the left:

4,500µL = 4.5mL = .0045L

You might wonder why scientists use a funky backward-looking-y for the abbreviation. That odd little character is a lowercase mu, the 13th letter of the Greek alphabet. They use it because the letter m already gets a lot of use in metrics. You already know that mL stands for milliliter and equals 1/1,000 of a liter, or 10–3 liters. If you change that to an uppercase M (which also happens to be an uppercase Mu), it becomes a megaliter, which is 1 million (or 106) liters. That leaves the lowercase µ for the microliter.

And that might help you remember the properties of megaliters and microliters. M is the first letter in the word million. One megaliter (ML) equals one million liters. One microliter (µL, lowercase mu) equals one millionth of a liter.