Scientists all over the world use the same units, the metric system, so they can share results. Its units grow by tens, hundreds and thousands, which makes them easy to change.
| What you measure | Tool | Units |
|---|---|---|
| Length | Ruler, meter stick, tape measure | 1 meter (m) = 100 centimeters (cm) |
| Mass | Balance or scale | 1 kilogram (kg) = 1,000 grams (g) |
| Liquid volume | Measuring cup, graduated cylinder | 1 liter (L) = 1,000 milliliters (mL) |
| Temperature | Thermometer | degrees Celsius (°C) or Fahrenheit (°F) |
| Time | Clock, timer | seconds, minutes, hours |
Key idea
Always write the unit. "The table is 2" could mean 2 meters or 2 centimeters, a big difference!
Worked example: Change the units
A string is 3 meters long. How many centimeters is that?
- 1 meter is 100 centimeters.
- 3 × 100 = 300.
Answer: 300 cm
Common mistake
Starting at 1 on the ruler, or reading a measuring cup from above. Start at 0, and bend down so your eyes are level with the liquid.
Try it at home
- Measure your hand span, a book and a spoon in centimeters.
- Pour water into a kitchen measuring cup and read it at eye level, then from above. Are they different?
- Weigh a bag of flour or rice on a kitchen scale and find its mass on the label. Do they agree?
Going further. The Math Ladder has whole lessons on measuring and changing units.