Mass: Grams and Kilograms

What you will learn

• Say what grams and kilograms measure.
• Choose a sensible unit.
• Convert between grams and kilograms.
• Solve simple mass problems.

Before you start: you should be able to compare heavy and light things and multiply by $1000$. See Comparing Length, Mass and Capacity.

The idea

Mass tells you how much matter is in an object. We often call it weight in daily life. The metric units are the gram (g) and the kilogram (kg). Kilo means a thousand, so $1$ kg is $1000$ g.

Choosing a unit

Use grams for light things (a coin, an apple, a bag of crisps) and kilograms for heavier things (a bag of potatoes, a person, a suitcase).

Reading scales

A scale has marks between the numbers. Work out what each mark is worth by dividing the gap between two numbers by the number of spaces. If $0$ and $500$ g have $5$ spaces between them, each mark is $100$ g.

Converting

Grams to kilograms: divide by $1000$. Kilograms to grams: multiply by $1000$.

Worked examples

Example 1: Convert

Change $2.5$ kg to grams.

1. Multiply by $1000$.
2. $2.5 \times 1000 = 2500$.

Answer: $2500$ g

Example 2: Subtract

A recipe needs $750$ g of flour from a $2$ kg bag. How much is left?

1. Change to grams: $2$ kg is $2000$ g.
2. $2000 - 750 = 1250$.

Answer: $1250$ g, which is $1.25$ kg.

Example 3: Total of several items

Three parcels weigh $1.2$ kg, $850$ g and $2$ kg. What is the total in kilograms?

1. Change to grams: $1200 + 850 + 2000 = 4050$ g.
2. Divide by $1000$: $4.05$ kg.

Answer: $4.05$ kg

Watch out: put every mass in the same unit before you add or compare.

Why it matters

Cooking, posting parcels, health and shopping all use mass. Knowing that $500$ g is half a kilogram helps you judge portions and compare prices.