Measure
Mass
Mass is the measure we use when we say that something is heavy or light. We weigh objects using grams and kilograms.
Grams and kilograms
We measure mass in grams (g) and kilograms (kg). • Grams are used for light things, like a peach or a chocolate bar. • Kilograms are used for heavy things, like a bag of potatoes. Always remember: 1 kilogram is equal to 1000 grams.
Reading a scale
A set of scales has a pointer that shows the mass. Read the number the pointer is nearest to. If a scale is marked in hundreds, a pointer on the 300 mark shows 300 g.
Comparing masses
We can compare masses using the signs <, > and =. • 300 g < 700 g (300 grams is lighter). • 1 kg = 1000 g (they are the same). • 900 g > 90 g (900 grams is heavier).
Taking grams from kilograms
When you subtract grams from kilograms, first change the kilograms into grams so both numbers use the same unit. Then subtract.
Worked examples
Changing kilograms to grams
- You have 2 kilograms.
- 1 kilogram is 1000 grams.
- So 2 kg = 2 × 1000 = 2000 grams.
Answer: 2 kg = 2000 g.
Taking grams from a kilogram
- Grandad has 1 kg of rice and cooks 350 g.
- Change 1 kg to 1000 g.
- Take 350 g away: 1000 − 350 = 650 g.
Answer: There are 650 g of rice left.
Comparing two masses
- Compare 300 g and 700 g.
- 300 is a smaller number than 700.
- So 300 g is lighter than 700 g.
Answer: 300 g < 700 g.
Working out one pear
- One peach weighs 80 g, so two peaches weigh 160 g.
- Four pears weigh the same as two peaches: 160 g.
- Share 160 g between 4 pears: 160 ÷ 4 = 40 g.
Answer: One pear weighs 40 g.
Where you see this in real life
- Weighing fruit and vegetables at the shop.
- Checking a suitcase is not too heavy before a flight.
- Following a recipe that needs 500 g of flour.
Key words
- Mass
- How heavy or light an object is.
- Gram (g)
- A small unit of mass, used for light objects.
- Kilogram (kg)
- A larger unit of mass. 1 kg = 1000 g.
- Scale
- An instrument that measures mass.