Concept 5 of 7
Decimals in Measurement: One Number, Two Forms
Today's big idea
The unit link sets the decimal places: cm fill two, g and mL fill three.
Read the unit before the digits, since 4.25 m and 4.25 cm share no size.
How it works
👀 What's going on?
The same shelf can be labelled 4 m 25 cm or 4.25 m. Nothing about the shelf has changed, only the way the number was written.
💡 Here's the trick
Look at the pairs above. The decimal places come straight from the unit link. Since 1 m is 100 cm, cm fill two places; since 1 kg is 1,000 g, g fill three.
🪄 How to do it
- 1.Check the link shown in the pairs above.
- 2.Count how many decimal places that link needs.
- 3.Fill every place, adding zeros where needed.
✍️ Try it
Write 5 m 8 cm as metres. Then: write 1.075 kg as kg and g.
Two places belong to cm, so 8 cm is 0.08 and you get 5.08 m. Three places belong to g, so 0.075 kg is 75 g, giving 1 kg 75 g.
⚠️ Watch out
You might be thinking 2 kg 40 g is written 2.4 kg. That skips a place. Notice that 40 g is 0.040 kg, so the right form is 2.04 kg.
🌟 Why this matters
Price labels, sports results and weather reports all use decimal measures. Reading 1.05 m as one metre and five cm saves you from silly slips at the shop.
Exam tip: Write the empty places first, then drop the digits in from the right.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“Write 3 m 5 cm in metres (decimal form).”
- 1
Count cm in 1 m
1 m = 100 cm → cm fit in 2 decimal places. 🔢
- 2
Convert the small unit
5 cm = 5/100 m = 0.05 m.
- 3
Add to the whole
3 + 0.05
- 4
Answer ✓
3 m 5 cm = 3.05 m
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
cm → m fills 2 decimal places · g → kg and m → km fill 3. Tap to slide the decimal in.
DECIMAL FORM · ROUND 1 OF 3
2 km 350 m
Quick check
✅ VERIFICATION
Which of these is the same as 2.6 kg?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Imperial Units
1 ft = 12 in · 1 yd = 3 ft · 1 lb = 16 oz.