Milli Micro Nano Pico

With electronics and time measurements, you will find those terms used often: milli, micro, nano, pico.

They are prefixes from the International System of Units, and each one is a thousand times smaller than the one before. Milli is a thousandth of a unit, micro is a millionth, nano is a billionth, pico is a trillionth.

This post is a quick reference to what each of them means:

• Milli (symbol m) = 10^-3 = 0,001
• Micro (symbol µ) = 10^-6 = 0,000 001
• Nano (symbol n) = 10^-9 = 0,000 000 001
• Pico (symbol p) = 10^-12 = 0,000 000 000 001

The order I used is important to remember what they mean: repeat it a few times, milli-micro-nano-pico and you’ll remember them the next time.

Where you’ll see them

Capacitors are the classic example. Electrolytic capacitors are measured in microfarads, like the 100µF ones you find near the power section of a circuit. Small ceramic capacitors are measured in picofarads, like the 22pF capacitors you pair with a quartz crystal.

Since µ is hard to type, you’ll often see it written as u: a 100µF capacitor is listed as 100uF in many part catalogs. Same thing.

Time works the same way. A millisecond is a thousandth of a second. When you call delay(2000) on an Arduino, you wait 2000 milliseconds, which is 2 seconds. delayMicroseconds(10) waits 10 millionths of a second.

Nanoseconds show up when you look at clock speeds. An Arduino Uno runs at 16 MHz, so a single clock cycle takes 62.5 nanoseconds.

Converting between them

To move from one prefix to the next, multiply or divide by 1000.

1 millisecond is 1000 microseconds. 1 microsecond is 1000 nanoseconds. 1 nanosecond is 1000 picoseconds.

So 1 millisecond is a million nanoseconds. When you convert, count the steps of 1000 between the two prefixes and you can’t go wrong.

Watch out for the case

One mistake to avoid: m and M are not the same thing. Lowercase m means milli, uppercase M means mega, which is a million times the unit.

Mix them up and you’re off by a factor of a billion. Datasheets are strict about this, part listings and forum posts not always, so when a value looks strange, check the case first.