Measure & compare temperature
Theory
Measuring and comparing temperature is a Year 4 measurement skill: reading a thermometer scale in degrees Celsius (°C) and deciding which temperature is warmer or cooler. The red column rises when it is hotter and falls when it is colder, so the temperature is read where the column stops. This Year 4 maths page shows how to work out the small marks, read the scale, and find how many degrees apart two temperatures are. Curriculum: VC2M4M01 / AC9M4M01.
Temperature tells you how hot or cold something is. In Australia it is measured in degrees Celsius, written °C (the small circle is the degree symbol).
A thermometer is like a number line standing up. A thin red column rises when it gets hotter and falls when it gets colder. You read the temperature where the top of the red column stops.
The big labelled marks are usually \(10\)°C apart, such as \(0\), \(10\), \(20\), \(30\). The small marks in between can each be worth \(1\)°, \(2\)° or \(5\)°, so always check them first. To compare two temperatures, the higher number is warmer and the lower number is cooler.
Temperature does not need formulas, but these Celsius benchmarks help you check a reading is sensible.
| Benchmark | Temperature |
|---|---|
| Water freezes (ice) | \(0\)°C |
| A cold winter morning | about \(5\)°C |
| A comfortable room | \(20\)–\(25\)°C |
| Normal body temperature | \(37\)°C |
| A hot summer day | about \(35\)°C |
| Water boils | \(100\)°C |
How to read and compare temperatures
- Check the marks. Look at two labelled numbers and count the small marks between them to work out how much each small mark is worth.
- Read the column. Find the nearest labelled mark below the top of the red column, then count on by the small-mark value to the top.
- Compare or subtract. The higher number is warmer. To find how many degrees apart two temperatures are, subtract the smaller from the larger.
- Rise or fall. When a temperature rises, add the degrees. When it falls, subtract them. Do one change at a time.
The top of the red column stops exactly on the \(10\) mark.
The temperature is \(10\)°C.
Start at \(30\) and count on in twos: \(32\).
The column stops one small mark above \(30\), so the temperature is \(32\)°C.
| \(\text{warmer} - \text{cooler}\) | \(=\) | \(23 - 9\) |
| \(23 - 9\) | \(=\) | \(14\) |
The afternoon was \(14\)°C warmer.
| \(\text{order}\) | \(:\) | \(8 < 19 < 31\) |
Coldest to hottest: \(8\)°C, \(19\)°C, \(31\)°C.
The column stops one small mark above \(20\). One small mark is \(5\) degrees, so the temperature is \(20 + 5 = 25\)°C.
| \(12 + 9\) | \(=\) | \(21\) |
| \(21 - 6\) | \(=\) | \(15\) |
It was \(21\)°C at lunchtime and \(15\)°C in the evening.
The column stops one small mark above \(38\), so the temperature is \(39\)°C. That is warmer than normal body temperature of about \(37\)°C, so it could be a fever.
Common pitfalls
Frequently asked questions
How do you read a thermometer?
Look at where the top of the red column stops. First work out how much each small mark is worth by looking at the labelled numbers, then count on from the nearest labelled mark. The temperature is read in degrees Celsius.
What unit is temperature measured in?
In Australia temperature is measured in degrees Celsius, written °C, for example \(20\)°C. The small circle is the degree symbol.
How do you work out how much warmer one temperature is than another?
Subtract the smaller temperature from the larger one. For example, \(9\)°C in the morning and \(23\)°C in the afternoon gives \(23 - 9 = 14\), so the afternoon is \(14\)°C warmer.
What is normal body temperature?
Normal body temperature is about \(37\)°C. A thermometer that reads much higher than this can be a sign of a fever.
At what temperature does water freeze and boil?
Water freezes at \(0\)°C and boils at \(100\)°C. These two numbers are useful benchmarks when you read a temperature.
Which is colder, 5 degrees or 12 degrees?
Five degrees is colder. The lower the number on the thermometer, the cooler it is, so \(5\)°C is colder than \(12\)°C.
How do you work out a temperature after it rises or falls?
Start with the first temperature. Add the degrees if it rises and subtract them if it falls. \(12\)°C that rises \(9\) degrees is \(21\)°C, and then falls \(6\) degrees to \(15\)°C.
How do you put temperatures in order?
Compare the numbers. The lowest number is the coolest and the highest is the warmest. \(8\)°C, \(19\)°C and \(31\)°C are in order from coolest to warmest.