Measuring mass
Mass tells us how heavy something is. We use grams (g) for light things and kilograms (kg) for heavier things.
Key idea
1 kg = 1000 g. To change kilograms to grams, multiply by 1000. To change grams to kilograms, divide by 1000.
Adding masses
We add or subtract mass just like numbers, keeping kilograms and grams together sensibly.
Worked example
A bag holds 500 g of rice and another holds 500 g. Together they are 500 + 500 = 1000 g = 1 kg.
We can also subtract mass. A melon weighs 2 kg. If we cut off a 500 g slice, how much is left? Change to grams: 2 kg = 2000 g, then 2000 − 500 = 1500 g = 1 kg 500 g. To go from grams back to kilograms we divide by 1000, so 3000 g ÷ 1000 = 3 kg. Using the same unit first makes every calculation easier.
Remember
- 1 kg = 1000 g.
- kg to g: multiply by 1000; g to kg: divide by 1000.
- Light things: grams. Heavy things: kilograms.