Measurement, Time, Money and Perimeter: Class 4 Study Guide
Measurement turns the world into numbers. Knowing the units and how to convert them is useful everywhere.
In the metric system 10 mm = 1 cm, 100 cm = 1 m and 1000 m = 1 km. For mass, 1000 g = 1 kg. For capacity, 1000 mL = 1 L. To change a bigger unit to a smaller one, multiply (3 km = 3 × 1000 = 3000 m). To change smaller to bigger, divide (4500 g = 4.5 kg).
Time is read on a 12-hour clock with a.m. (midnight to noon) and p.m. (noon to midnight), and on a 24-hour clock (14:30 is 2:30 p.m.). Perimeter is the total distance around a shape.
Converting units
| From | To | Operation | Example |
|---|---|---|---|
| m | cm | × 100 | 3 m = 300 cm |
| km | m | × 1000 | 2 km = 2000 m |
| kg | g | × 1000 | 5 kg = 5000 g |
| L | mL | × 1000 | 2 L = 2000 mL |
| cm | m | ÷ 100 | 450 cm = 4.5 m |
Perimeter
To find the perimeter, add the lengths of all the sides. A rectangle of 8 cm by 5 cm has perimeter 8 + 5 + 8 + 5 = 26 cm, or 2 × (8 + 5). A square of side 6 cm has perimeter 4 × 6 = 24 cm. A fence around a field is an example of perimeter.
8, 5, 8, 5.
26.
26 cm.
Did you include every side?
Time and money
A train leaves at 14:15 and arrives at 17:40. The journey takes 3 hours 25 minutes (14:15 to 17:15 is 3 h, then 25 min). Money: ₹1 = 100 paise. If a book costs ₹85 and a pen ₹35, the total is ₹120. If you pay ₹200, your change is ₹80.
Worked examples and common mistakes
Example: 3 kg 250 g = 3250 g. Example: 6:45 p.m. in 24-hour time is 18:45. Common mistakes: forgetting to convert units before adding, leaving out a side when finding perimeter and mixing up a.m. and p.m. Write units next to every number.
Check your understanding: model answers
1. 5300 m. 2. 2 × (12 + 7) = 38 cm. 3. 21:30.
✨ Key Takeaways
- Multiply to convert big units to small; divide to convert small to big.
- Perimeter is the sum of all sides.
- 24-hour time: add 12 to p.m. hours.
- Always write the unit.
💬 Questions for Discussion & Reflection
- Convert 5 km 300 m to metres.
- Find the perimeter of a rectangle 12 cm by 7 cm.
- What is 9:30 p.m. in 24-hour time?
Print graph paper for perimeter drawings →