Hot or cold?
Temperature tells how hot or cold something is. We measure it with a thermometer in degrees.
Two scales
| Scale | Symbol | Water freezes | Water boils | Used in |
|---|---|---|---|---|
| Degrees Celsius | °C | 0 °C | 100 °C | Canada, most countries |
| Degrees Fahrenheit | °F | 32 °F | 212 °F | United States |
Canada uses Celsius for weather, but you’ll still hear Fahrenheit for ovens and pools.
Benchmark temperatures in Celsius
| Temperature | What it feels like |
|---|---|
| −30 °C | a bitter winter day on the Prairies |
| −10 °C | a cold winter day |
| 0 °C | freezing point of water |
| 10 °C | a cool spring day: wear a jacket |
| 20 °C | room temperature |
| 30 °C | a hot summer day |
| 37 °C | normal body temperature |
| 100 °C | boiling point of water at sea level |
| 180 °C | a moderate oven |
Reading a thermometer
- Find what each mark stands for. If there are 5 small marks between 0 and 10, each mark is 2 degrees.
- Read the top of the red (or silver) column.
- If the column is below zero, read the negative numbers: they get colder as you go down.
Negative temperatures
Temperatures below 0 °C are written with a minus sign: −5 °C is "minus five" or "five below zero". −15 °C is colder than −5 °C.
Temperature changes
Use a number line (or the thermometer itself) to find changes.
- From −4 °C to 6 °C: 4 degrees up to 0, then 6 more = 10 degrees warmer.
- From 12 °C to −3 °C: 12 down to 0, then 3 more = 15 degrees colder.
Converting (for interest)
- °F = °C × 9/5 + 32
- 20 °C → 20 × 1.8 + 32 = 68 °F
A rough rule: double the Celsius and add 30 (20 °C → 70 °F).
Worked examples
Example 1: A thermometer reads 25 °C. Is it a good day for the beach?
Yes, it’s warm.
Example 2: Overnight the temperature drops from 3 °C to −8 °C. How much did it drop?
3 + 8 = 11 degrees.
Example 3: Which is colder: −12 °C or −7 °C?
−12 °C (it’s further below zero).
Common mistakes
- Reading below-zero numbers upward, so −8 looks warmer than −2.
- Forgetting the degree symbol and scale.
- Thinking 0 °C means "no temperature". It’s just where water freezes.
Try it yourself
- What temperature does water freeze at in Celsius?
- Which is warmer: −3 °C or −10 °C?
- The temperature rises from −6 °C to 4 °C. By how much?
- Normal body temperature is about how many °C?
Answers: 1) 0 °C 2) −3 °C 3) 10 degrees 4) 37 °C
Quick recap
- A thermometer measures temperature in degrees Celsius (or Fahrenheit).
- Water freezes at 0 °C and boils at 100 °C.
- Numbers below zero get colder as they get further from 0.