Most of the world uses the decimalized metric system which is officially called the "International System of Units". SI units include:

**Length**- metre**Mass**- kilogram**Capacity**- litre

Prefixes used at the beginning of each of these units are shown in the table.

LATIN PREFIXES FOR SMALLER UNITS | |

nano- | 1 billionth OR 1/ 1 000 000 000 |

micro- | 1 millionth OR 1/ 1 000 000 |

milli- | 1 thousandth OR 1/ 1000 |

centi- | 1 hundredth OR 1/ 100 |

GREEK PREFIXES FOR LARGER UNITS | |

kilo- | 1 thousand OR 1000 |

mega- | 1 million OR 1 000 000 |

giga- | 1 billion OR 1 000 000 000 |

The **metre** was originally defined as the distance between the North Pole and the Equator divided by ten million.
Now it is defined as the distance light travels in a vacuum in 1/ 299 792 458 parts of a second.

LENGTH RULES |
CONVERTING LENGTH UNITS |

10 millimetres = 1 centimetre
1000 millimetres = 1 metre 100 centimetres = 1 metre 1000 metres = 1 kilometre |
When converting from
large unit to a small unit, you multiply.
When converting from a small unit to a large unit, you divide. |

**Q1.** 5 km = m
**Q2.** 3.5 m = cm
**Q3.** 34.6 cm = mm

**Answers:**
**A1.** 5000
**A2.** 350
**A3.** 346

**Q4.** 6500 m = km
**Q5.** 43.8 cm = m
**Q6.** 3192 mm = m

**Answers:**
**A4.** 6.5
**A5.** 0.438
**A6.** 3.192

Complete these length conversions.

**Q1.** 64.7 km = m
**Q2.** 63 m = km
**Q3.** 0.4 m = cm
**Q4.** 8.4 mm = cm
**Q5.** 0.9 km = mm

**Answers**
**A1.** 64700
**A2.** 0.063
**A3.** 40
**A4.** 0.84
**A5.** 900000

**PERIMETER**

In the word perimeter, **"peri" means "around"** and **"meter" means "measure"**. Therefore, to find the perimeter is to measure around the boundary of an object.
Perimeter is **measured in metres**. Examples where Perimeter is calculated are the length of:

- a
**fence**around a farm - a
**frame**around a picture **garden edging**around a garden**guttering**around a house**cornice**around the ceiling of a room

**AREA**

Area is the **flat or two dimensional size** of an object. Area is **measured in square metres (m ^{2})**. Examples include the Area to:

- make clothes from
**fabric** **paint**a wall**tile**a floor- work out the
**cost of glass window panes** - make
**curtains** - lay
**turf (grass)** - spread
**fertilizer**on a garden

**VOLUME**

Volume is the **solid or space inside or the three-dimensional size** of an object. Volume is **measured in cubic metres (m ^{3})**.
If gas or liquid is measured, it is called capacity and is measured in

**rock**in a quarry**plastic**in a plumbing pipe**concrete slabs****air**in a room (air-conditioning)**gas**in a barbecue gas bottle**gasoline (petrol)**in a car's tank**milk**in a carton**water**in a rainwater tank or a swimming pool

When you last ate chocolate, did you consider how far the main ingredients - **cocoa, sugar, palm oil and vanilla** - have travelled to get to your mouth?
Brown Cocoa Solids from the cacao tree are primarily grown in Ivory Coast in Africa; Sugar from sugar cane comes mainly from Brazil;
Palm Oil is a major export of Indonesia; and Vanilla (the second most expensive flavouring in the world after saffron) is also predominantly cultivated in Indonesia.
Use an atlas to estimate the **"food miles" or "food kilometres"** that these ingredients travelled from the plants to your mouth.