Measurement · Lesson 15 of 16

Temperature and Thermometers

Temperature tells us how hot or cold something is. We read it in degrees Celsius on a scale, and numbers below zero mean colder than freezing.

Primary
Updated 14 November 2026

What you will learn

Read a thermometer scale.
Use negative temperatures.
Find rises, falls and differences.

Before you start: you should be able to count in tens and compare numbers. See Units of Measurement.

The idea

Temperature tells us how hot or cold something is. We measure it with a thermometer in degrees Celsius ( $^\circ\text{C}$ ). The thermometer has a scale of marks, and the top of the liquid shows the temperature.

Two thermometers. One reads 23 degrees, a warm day. The other reads -4 degrees, below freezing.

Reading the scale

First find how much each small mark is worth. Look at the numbers on two long marks and count the gaps between them. Then read the top of the liquid.

Important temperatures

Three useful temperatures to remember: water freezes at 0, the body is about 37 and water boils at 100 degrees Celsius.

Below zero

Temperatures below $0$ are written with a minus sign. $-5^\circ\text{C}$ is colder than $-2^\circ\text{C}$ . On a vertical scale, going up means warmer and going down means colder.

Rises, falls and differences

To find how much the temperature changed, subtract the start from the end. To find a difference across zero, count up to zero and then on to the other number.

From -5 to 4 degrees is a rise of 5 + 4 = 9 degrees.

Worked examples

Example 1: A rise

At 6 am it is $-2^\circ\text{C}$ . By 2 pm it is $9^\circ\text{C}$ . How many degrees did it rise?

From $-2$ to $0$ is $2$ degrees.
From $0$ to $9$ is $9$ degrees.
$2 + 9 = 11$ .

Answer: $11$ degrees

Example 2: A fall

The temperature is $3^\circ\text{C}$ . It falls by $7$ degrees. What is it now?

$3 - 7 = -4$ .

Answer: $-4^\circ\text{C}$

Example 3: Reading a scale

A thermometer has long marks at $20$ and $30$ with $5$ gaps between them. The liquid is at the third small mark after $20$ . What is the temperature?

Each gap is $10 \div 5 = 2$ degrees.
Three gaps is $3 \times 2 = 6$ .
$20 + 6 = 26$ .

Answer: $26^\circ\text{C}$

Tip: draw a quick vertical number line. It makes rises and falls across zero much easier to see.

Why it matters

Temperature matters for weather forecasts, cooking, health checks and safety. A fever, a frost warning and an oven setting all depend on reading a scale correctly. For changing between Celsius and Fahrenheit, see Unit Conversions.

Practice

Your turn. Type or choose an answer, then press Check. Getting one wrong is fine, that is what practice is for. You can try as many times as you like.