Year 5: Approximate metric and imperial units
Part of the Year 5 units, perimeter, area, volume and time chapter. Chapter overview · whole chapter on one page
Approximate metric and imperial units
Some things are still measured in imperial units. You may see inches on a screen or a ruler, pounds on some food packets and pints of milk. An imperial unit does not fit exactly into a metric unit, so we use the word about.
| Measure | Imperial unit | Approximate metric equivalent |
|---|---|---|
| Length | 1 inch | ≈ 2.5 cm |
| Mass | 1 pound (lb) | ≈ 450 g |
| Mass | 2.2 pounds | ≈ 1 kg |
| Capacity | 1 pint | ≈ 0.57 litres |
| Capacity | 1.75 pints | ≈ 1 litre |
To change inches to centimetres, multiply by 2.5. To change kilograms to pounds, multiply by 2.2. To change litres to pints, multiply by 1.75. To change in the other direction, divide.
Key ideas
- Imperial units are only approximate in metric. Use the word about in your answer.
- Inches to centimetres: multiply by 2.5. Centimetres to inches: divide by 2.5.
- 1 kg ≈ 2.2 pounds, and 1 litre ≈ 1.75 pints.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 inch ≈ 2.5 cm
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.10 × 2.5 = 25
- Write the answer with the new unit. about 25 cm
Check. 25 ÷ 2.5 = 10, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 kg ≈ 2.2 pounds
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.5 × 2.2 = 11
- Write the answer with the new unit. about 11 pounds
Check. 11 ÷ 2.2 = 5, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 litre ≈ 1.75 pints
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.2 × 1.75 = 3.5
- Write the answer with the new unit. about 3.5 pints
Check. 3.5 ÷ 1.75 = 2, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Watch out
Do not write exactly 25 cm for 10 inches or exactly 11 pounds for 5 kg. These are approximate conversions, so write about in your answer.Exercise 8B Inches, pounds and pints
Non-calculatorKey words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 inch ≈ 2.5 cm
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.4 × 2.5 = 10
- Write the answer with the new unit. 10 cm
Check. 10 ÷ 2.5 = 4, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 inch ≈ 2.5 cm
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.12 × 2.5 = 30
- Write the answer with the new unit. 30 cm
Check. 30 ÷ 2.5 = 12, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 inch ≈ 2.5 cm
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.8 × 2.5 = 20
- Write the answer with the new unit. 20 cm
Check. 20 ÷ 2.5 = 8, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 inch ≈ 2.5 cm
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.10 × 2.5 = 25
- Write the answer with the new unit. 25 cm
Check. 25 ÷ 2.5 = 10, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.2.5 cm ≈ 1 inch
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.15 ÷ 2.5 = 6
- Write the answer with the new unit. 6 inches
Check. 6 × 2.5 = 15, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.2.5 cm ≈ 1 inch
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.20 ÷ 2.5 = 8
- Write the answer with the new unit. 8 inches
Check. 8 × 2.5 = 20, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.2.5 cm ≈ 1 inch
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.5 ÷ 2.5 = 2
- Write the answer with the new unit. 2 inches
Check. 2 × 2.5 = 5, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.2.5 cm ≈ 1 inch
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.10 ÷ 2.5 = 4
- Write the answer with the new unit. 4 inches
Check. 4 × 2.5 = 10, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 kg ≈ 2.2 pounds
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.2 × 2.2 = 4.4
- Write the answer with the new unit. 4.4 pounds
Check. 4.4 ÷ 2.2 = 2, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 kg ≈ 2.2 pounds
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.5 × 2.2 = 11
- Write the answer with the new unit. 11 pounds
Check. 11 ÷ 2.2 = 5, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 kg ≈ 2.2 pounds
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.10 × 2.2 = 22
- Write the answer with the new unit. 22 pounds
Check. 22 ÷ 2.2 = 10, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 kg ≈ 2.2 pounds
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.0.5 × 2.2 = 1.1
- Write the answer with the new unit. 1.1 pounds
Check. 1.1 ÷ 2.2 = 0.5, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.2.2 pounds ≈ 1 kg
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.11 ÷ 2.2 = 5
- Write the answer with the new unit. 5 kg
Check. 5 × 2.2 = 11, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.2.2 pounds ≈ 1 kg
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.22 ÷ 2.2 = 10
- Write the answer with the new unit. 10 kg
Check. 10 × 2.2 = 22, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.2.2 pounds ≈ 1 kg
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.4.4 ÷ 2.2 = 2
- Write the answer with the new unit. 2 kg
Check. 2 × 2.2 = 4.4, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.2.2 pounds ≈ 1 kg
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.2.2 ÷ 2.2 = 1
- Write the answer with the new unit. 1 kg
Check. 1 × 2.2 = 2.2, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 litre ≈ 1.75 pints
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.4 × 1.75 = 7
- Write the answer with the new unit. 7 pints
Check. 7 ÷ 1.75 = 4, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 litre ≈ 1.75 pints
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.2 × 1.75 = 3.5
- Write the answer with the new unit. 3.5 pints
Check. 3.5 ÷ 1.75 = 2, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 litre ≈ 1.75 pints
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.8 × 1.75 = 14
- Write the answer with the new unit. 14 pints
Check. 14 ÷ 1.75 = 8, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1.75 pints ≈ 1 litre
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.7 ÷ 1.75 = 4
- Write the answer with the new unit. 4 litres
Check. 4 × 1.75 = 7, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1.75 pints ≈ 1 litre
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.3.5 ÷ 1.75 = 2
- Write the answer with the new unit. 2 litres
Check. 2 × 1.75 = 3.5, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1.75 pints ≈ 1 litre
- Divide, because the new unit is bigger. A bigger unit fits in fewer times, so the number gets smaller.14 ÷ 1.75 = 8
- Write the answer with the new unit. 8 litres
Check. 8 × 1.75 = 14, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. A unit is the size we measure with. Metric units go up in tens, hundreds and thousands, so we convert between them by multiplying or dividing. A smaller unit gives a bigger number.
Method. Use the rule to see how many of the new unit there are. Multiply for a smaller unit, and divide for a bigger unit.
- Write the rule. This rule links the two units, so we know how many of the smaller one make the bigger one.1 pint ≈ 0.57 litres
- Multiply, because the new unit is smaller. A smaller unit fits in more times, so the number gets bigger.2 × 0.57 = 1.14
- Write the answer with the new unit. about 1.14 litres
Check. 1.14 ÷ 0.57 = 2, which is the number we started with. ✓
Watch out. Check the size: a smaller unit must give a bigger number, and a bigger unit must give a smaller number.
Key words. Imperial units are older units, such as inches, pounds and pints. The symbol ≈ means “is about equal to”, so our answers are estimates.
Method. Change both weights to the same unit. Then compare.
- Write 1 kg in pounds. 1 kg is about 2.2 pounds.1 kg ≈ 2.2 pounds
- Compare with the 2 pound bag. Is 2.2 pounds more than 2 pounds?2.2 pounds > 2 pounds
- Write the answer. Yes. The 1 kg bag is heavier.
Check. 1 kg is about 0.2 pounds more than 2 pounds. ✓
Watch out. Two numbers of different units cannot be compared until they are changed to the same unit.
Key words. Imperial units are older units, such as inches, pounds and pints. The symbol ≈ means “is about equal to”, so our answers are estimates.
Method. Change 12 inches to centimetres, then compare with 30 cm.
- Change 12 inches to centimetres. Multiply the inches by 2.5.12 × 2.5 = 30 cm
- Compare the two rulers. Both rulers are about 30 cm long.30 cm ≈ 30 cm
- Write the answer. They are about the same length.
Check. 12 inches is about 30 cm, so the two rulers are about the same length. ✓
Watch out. The two lengths are approximately the same. Check the answer with the rule 1 inch ≈ 2.5 cm.
Key words. Imperial units are older units, such as inches, pounds and pints. The symbol ≈ means “is about equal to”, so our answers are estimates.
Method. Change 500 g to kilograms, then to pounds.
- Change 500 g to kilograms. There are 1,000 g in 1 kg, so 500 g is half a kilogram.500 g = 0.5 kg
- Change kilograms to pounds. Multiply the kilograms by 2.2, because 1 kg is about 2.2 pounds.0.5 × 2.2 = 1.1
- Write the answer. The answer is an estimate, so write about.about 1.1 pounds
Check. Half of 2.2 pounds is 1.1 pounds, so about 1.1 pounds is right. ✓
Watch out. Change grams to kilograms first. Do not multiply 500 by 2.2.