Success criteria
- I choose a conversion fact that matches the units.
- I multiply to rename a larger unit as smaller units and divide to reverse it.
- I apply
A = length × widthand label the result in square metric units. - I estimate first and explain why my result is reasonable.
Learn and explain
A measurement does not change when its unit changes. Only its name and number change. Since 1 metre is 100 centimetres, 2.7 metres is 270 centimetres. The number grows because centimetres are smaller pieces.
| Relationship | Larger → smaller | Smaller → larger |
|---|---|---|
| 1 m = 100 cm | × 100 | ÷ 100 |
| 1 kg = 1,000 g | × 1,000 | ÷ 1,000 |
| 1 L = 1,000 mL | × 1,000 | ÷ 1,000 |
| 1 hour = 60 min | × 60 | ÷ 60 |
Say aloud: “I used ___ because ___. My answer should be larger/smaller because ___.”
From length to area
Length measures one direction, but area counts square units covering a surface. A rectangle measuring 12 cm by 7 cm has area 12 × 7 = 84 cm². Multiplying two centimetre measurements produces square centimetres, not centimetres.
Independent practice
Convert 3.4 kg to grams.
3.4 × 1,000 = 3400 g.
Convert 1.25 L to millilitres.
1.25 × 1,000 = 1250 mL.
A ribbon is 460 cm long. Which operation converts it to metres?
A metre is larger than a centimetre, so fewer metres name the same length.
Find the area of a rectangle measuring 12 cm × 7 cm.
12 × 7 = 84 square centimetres.
Unfamiliar transfer — journey card
A ferry journey starts at 8:47 and ends at 10:12. Without a calculator, draw a time line, find the duration in minutes, then check below.
What is the journey duration?
13 minutes to 9:00, then 60 minutes, then 12 minutes: 85 minutes.
Delayed check
One week later, without this table: convert 4,750 mL to litres and explain why the answer must be between 4 and 5. Then sketch a metric rectangle, calculate its area, and explain why its unit is squared. Record whether both methods were independent.
Evidence path
Save a photo or scan of the journey time line and explanation to jeremy/portfolio/math/unit-4/lesson-11-conversions/.
Next step
- Repair: mix up the direction? Build one metre and one litre reference card.
- Continue: accurate and explained? Move to volume.
- Stretch: create a two-step conversion involving hours and minutes or metres and centimetres.