A complete and child-friendly guide to metric, imperial and time conversions for school maths, everyday life and 11+ preparation.
In maths, we often need to change one unit into another. For example, a distance might be given in metres but the answer may be needed in centimetres. A journey might be shown in miles, while a science question may ask for kilometres. Once children understand the pattern, unit conversion becomes much easier and much quicker.
Metric ladder: km → m → cm → mm
Metric length units are used for measuring distance and size. These are the most common conversions children learn first.
| Unit | Conversion | Helpful Note |
|---|---|---|
| 1 kilometre (km) | 1000 metres (m) | Used for longer distances such as roads and journeys. |
| 1 metre (m) | 100 centimetres (cm) | A metre is a little longer than a yard. |
| 1 centimetre (cm) | 10 millimetres (mm) | Used for smaller lengths such as pencil width or tiny gaps. |
| 1 metre (m) | 1000 millimetres (mm) | Useful when converting from m directly to mm. |
These units are used for measuring how heavy something is.
| Unit | Conversion | Helpful Note |
|---|---|---|
| 1 tonne (t) | 1000 kilograms (kg) | Used for very heavy things like lorries. |
| 1 kilogram (kg) | 1000 grams (g) | Common for food, bags and body weight. |
| 1 gram (g) | 1000 milligrams (mg) | Used for tiny masses such as medicine doses. |
Capacity tells us how much liquid a container can hold, while volume measures the space something takes up.
| Unit | Conversion | Helpful Note |
|---|---|---|
| 1 litre (L) | 1000 millilitres (mL) | Very common in bottles and measuring jugs. |
| 1 cubic metre (m³) | 1000 litres | Used for larger spaces or large amounts of liquid. |
| 1 cubic centimetre (cm³) | 1 millilitre (mL) | A very important science conversion. |
Imperial units are still seen in the UK, especially for road distances, height and everyday conversation.
| Unit | Conversion | Helpful Note |
|---|---|---|
| 12 inches | 1 foot (ft) | Often used for height. |
| 3 feet | 1 yard (yd) | Useful in sports and fabric measurements. |
| 1760 yards | 1 mile (mi) | Miles are used on UK road signs. |
| 1 inch | 2.54 centimetres | One of the most useful exact conversions. |
| 1 foot | 30.48 centimetres | Helpful when converting people’s heights. |
| 1 yard | 0.914 metres | Approximate classroom conversion. |
| 1 mile | 1.609 kilometres | Often rounded to 1.6 km. |
These are older units but still appear in everyday life and some exam questions.
| Unit | Conversion | Helpful Note |
|---|---|---|
| 16 ounces (oz) | 1 pound (lb) | Pounds are still used for some weights. |
| 14 pounds | 1 stone (st) | Stone is often used for body weight in the UK. |
| 20 fluid ounces | 1 pint | Pints are common for milk and some drinks. |
| 2 pints | 1 quart | Older unit, less common now. |
| 4 quarts | 1 gallon (UK) | Still useful to know for mixed conversion questions. |
| 1 gallon (UK) | 4.546 litres | Very common metric-imperial conversion. |
| 1 litre | 1.76 pints | Often rounded in mental maths questions. |
| 1 kilogram | 2.2 pounds | Useful for converting between metric and imperial weight. |
| 1 pound | 0.45 kilograms | Approximate reverse conversion. |
Time conversions are essential for timetables, duration questions and exam problem solving.
| Unit | Conversion | Helpful Note |
|---|---|---|
| 60 seconds | 1 minute | Basic time fact to know by heart. |
| 60 minutes | 1 hour | Used in almost every time problem. |
| 24 hours | 1 day | Helpful when working with full-day timetables. |
| 7 days | 1 week | Used for calendars and planning. |
| 12 months | 1 year | Another basic fact for date questions. |
| 365 days | 1 year | Normal year. |
| 366 days | 1 leap year | Leap years have one extra day in February. |
These extra conversions appear in more advanced school maths and are very useful revision facts.
| Type | Conversion | Helpful Note |
|---|---|---|
| Speed | 1 mph ≈ 1.6 km/h | Common in road-speed questions. |
| Speed | 1 km/h ≈ 0.62 mph | Reverse conversion. |
| Area | 1 m² = 10,000 cm² | Remember area units are squared. |
| Area | 1 km² = 1,000,000 m² | Very large area conversion. |
| Area | 1 hectare = 10,000 m² | Used for land area. |
| Area | 1 acre ≈ 4047 m² | Older land measurement. |
| Volume | 1 m³ = 1000 L | Very useful in capacity and volume problems. |
When you convert to a smaller unit, the number usually gets bigger. When you convert to a bigger unit, the number usually gets smaller.
Always look at the unit in the final answer. Many children do the maths correctly but leave the answer in the wrong unit.
Mixed unit word problems often test more than one skill at once, such as time plus money, or distance plus speed.
