2
Grams or kilograms?
Discover Mathematics P3: Term 2, Lessons 71–80
GoalChoose grams or kilograms for an object and change between them using 1 kg = 1,000 g.
New words
mass · how heavy something isgram (g) · a small unit of masskilogram (kg) · a bigger unit of mass; 1 kg is 1,000 g
Explanation
Mass tells us how heavy something is. We use grams (g) for light things and kilograms (kg) for heavy things. A pencil has a mass of about 5 g and an apple about 150 g. A school bag has a mass of about 3 kg and a watermelon about 4 kg. The units are connected: 1 kg = 1,000 g. To change kilograms to grams, multiply by 1,000: 2 kg = 2,000 g. To change grams to kilograms, divide by 1,000: 3,000 g = 3 kg. A mass such as 1 kg 500 g is 1,000 g + 500 g = 1,500 g.
Worked examples
Which unit? An egg is light, so we use grams: about 60 g. A sack of rice is heavy, so we use kilograms: about 5 kg.
| Kilograms | Grams |
|---|---|
| 1 | 1,000 |
| 2 | 2,000 |
| 5 | 5,000 |
| 8 | 8,000 |
A mass of 1 kg 500 g is 1,000 g + 500 g = 1,500 g.
Class activity
Weigh it. With an adult, find five things at home that have their mass printed on the label, such as rice, sugar, tea, a tin of beans or a box of biscuits. Write each mass with its unit. Which are in grams and which are in kilograms? Order them from lightest to heaviest.
Practice
1
Choose g or kg for each: a banana, a school bag, a coin, a sack of flour.
A banana: g. A school bag: kg. A coin: g. A sack of flour: kg.
2
How many grams are in 4 kg?
4 × 1,000 = 4,000 g.
3
How many kilograms are in 7,000 g?
7,000 ÷ 1,000 = 7 kg.
4
Four apples of 250 g each are on one side of the scale. What mass must be on the other side so that the scale balances?
4 × 250 = 1,000 g, which is 1 kg.
5
Which is heavier: 2,500 g or 2 kg?
2 kg = 2,000 g, and 2,500 g is more than 2,000 g, so 2,500 g is heavier.