A thermometer is a scale that stands up. The labels usually go up by 10 degrees. Count the spaces between two labels to find what each mark is worth: 10 spaces means 1 degree each, 5 spaces means 2 degrees each. Find the top of the liquid, start at the label just below it and count up. Below zero the numbers are negative and get colder as you go down: the mark just under 0 is −1 or −2, not −9. Count down from 0 to read them.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- degree Celsius
- the unit of temperature, written °C
- negative temperature
- a temperature colder than 0 °C, written with a minus sign
- thermometer
- a tool that measures temperature
Worked examples
Labels every 10 with 10 spaces between. The liquid stops 7 marks above 20. What temperature, in °C?
- 1.Each mark is 1 degree.
- 2.20 + 7 = 27.
= 27
Labels every 10 with 5 spaces between. The liquid stops 3 marks above 30. What temperature, in °C?
- 1.10 ÷ 5 = 2, so each mark is 2 degrees.
- 2.3 × 2 = 6, and 30 + 6 = 36.
= 36
Labels every 10 with 5 spaces between. The liquid stops 2 marks below 0. What temperature, in °C?
- 1.Each mark is 2 degrees.
- 2.Count down from 0: −2, −4.
= -4
For parents
Method: Find the mark value, then count from the nearest label
What to say: What is each mark worth? Is the liquid above or below zero?
Common mistakes:
- Assumes every mark on the thermometer is 1 degree, even when there are fewer marks between labels.
- Reads a temperature below zero as if it were above zero, dropping the minus sign.
- Below zero, counts up from the lower label as if numbers still got bigger going up (reads −4 as −6).
- Counts the labelled mark as the first step, so reads one mark too high.
- Reads the labelled temperature just below the liquid and ignores the extra marks.