# Scales and Sizes of Cells

Cells and sub-cellular structures are very small. In order to describe their sizes, you need to be familiar with the various units that can be used to measure small distances, and you need to know how to convert between these units.

## Centimetres (cm)

A centimetre is a hundredth of a metre. In other words, a centimetre is 0.01m, or in standard form 1 x 10-2m.

Centimetres are abbreviated to cm. There are 100 centimetres in a metre.

## Millimetres (mm)

A millimetre is a thousandth of a metre (that is, a tenth of a centimetre). Therefore, a millimetre is 0.001m or in standard form 1 x 10-3m.

Millimetres are abbreviated to mm. There are 1000 millimetres in a metre.

## Micrometres (μm)

A micrometre is a thousand times smaller than a millimetre. Therefore a micrometre is a millionth of a metre, which can be written as 0.000001m or in standard form as 1 x 10-6m.

Micrometres are abbreviated to μm. The symbol 'μ' is a Greek letter called mu. There are 1000 micrometres in a millimetre.

## Nanometres (nm)

A nanometre is a thousand times smaller than a micrometre. Therefore, a nanometre is a billionth of a metre, written as 0.000000001 or in standard form as 1 x 10-9m.

Nanometres are abbreviated to nm. There are 1000 nanometres in a micrometre.

## Converting between units of length

To convert a measurement from one unit of length to another, we first need to know how many times bigger or smaller the new unit is than the old one.

For example, suppose we are converting from centimetres to millimetres. A millimetre is ten times smaller than a centimetre, so the number we need is 10.

Or suppose we are converting from nanometres to micrometres. A micrometre is a thousand times bigger than a nanometre, so in this case the number we need is 1000.

What we do with this number depends on whether we are going to a bigger unit or a smaller one:

If we are converting from a smaller unit to a bigger one (e.g. nanometres to micrometres) then we divide by the number (e.g. ÷1000).

If we are converting from a bigger unit to a smaller unit (e.g. centimetres to millimetres) then we multiply by the number (e.g. x10). Converting between units of length.

## Unit conversion examples

Example 1: Convert 0.046mm to μm.

A micrometres is a thousand times smaller than a millimetre. Therefore, we multiply by 1000:

0.046 x 1000 = 46μm

Example 2: Convert 863nm to μm.

A micrometre is a thousand times bigger than a nanometre. Therefore, we divide by 1000:

863 ÷ 1000 = 0.863μm

## Flashcards

Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.

1/5

What are centimetres and what are they abbreviated to?

2/5

What are millimetres and what are they abbreviated to?

3/5

What are micrometres and what are they abbreviated to?

4/5

What are nanometres and what are they abbreviated to?

5/5

How do you convert between units of measurement?