The metric system is built around a base unit — metres for length, grams for mass, litres for capacity — with prefixes like kilo, centi and milli used to scale it up or down. Every step between one prefix and the next is a power of 10, so converting means multiplying or dividing by 10, 100 or 1000.
Quantity
Small
Medium
Large
Length
millimetres (mm)
centimetres (cm), metres (m)
kilometres (km)
Mass
milligrams (mg)
grams (g)
kilograms (kg), tonnes (t)
Capacity
millilitres (ml)
centilitres (cl)
litres (l)
Prefix meanings: kilo- = 1000 | centi- = 1/100 | milli- = 1/1000
So 1 kilometre = 1000 metres, 1 centimetre = 1/100 of a metre, 1 millimetre = 1/1000 of a metre.
Key pattern: km → m skips 3 steps on the staircase, so ×10 × 10 × 10 = ×1000. The same applies to kg → g and l → ml.
Memory aid: Think of converting km to m — 1 km = 1000 m, so you need more metres. More = multiply. Going the other way, 1000 m = 1 km — you end up with fewer of them. Fewer = divide.
✓ Quick Check 1 — Basic Metric Conversions
Question 1 of 10
Worked Examples
Example 1: Convert 3.5 km to metres
Step 1 — Identify direction
km → m: going from bigger to smaller unit, so we multiply.
Step 2 — Apply factor
km to m: multiply by 1000 \(3.5 \times 1000 = \mathbf{3500\text{ m}}\)
Example 2: Convert 4500 g to kilograms
Step 1 — Identify direction
g → kg: going from smaller to bigger unit, so we divide.
Step 2 — Apply factor
g to kg: divide by 1000 \(4500 \div 1000 = \mathbf{4.5\text{ kg}}\)
Example 3: Convert 250 cm to metres
Step 1 — Identify direction
cm → m: going from smaller to bigger unit, so we divide.
Step 2 — Apply factor
cm to m: divide by 100 \(250 \div 100 = \mathbf{2.5\text{ m}}\)
Example 4: Convert 3.2 litres to millilitres
Step 1 — Identify direction
l → ml: going from bigger to smaller unit, so we multiply.
Step 2 — Apply factor
l to ml: multiply by 1000 \(3.2 \times 1000 = \mathbf{3200\text{ ml}}\)
Example 5: Convert 850 mm to centimetres
Step 1 — Identify direction
mm → cm: going from smaller to bigger unit, so we divide.
Step 2 — Apply factor
mm to cm: divide by 10 \(850 \div 10 = \mathbf{85\text{ cm}}\)
Example 6: Convert 2 m 35 cm into a single unit — mixed units
Step 1 — Convert each part to the same unit
Convert the metres part to cm: \(2 \text{ m} = 2 \times 100 = 200\text{ cm}\). The 35 cm is already in cm.
💡 The same idea works in reverse — to write 235 cm as "2 m 35 cm," divide by 100 to find the whole metres (\(235 \div 100 = 2\) remainder 35), and the remainder is the leftover cm.
Example 7: Choosing the appropriate unit
Reasoning
Ask: "is this measurement realistically a small number of mm/ml/g, or would that be an awkwardly huge number?" A car's mass in grams would be a number like 1,500,000 — technically correct but impractical. The appropriate unit is the one that keeps the number in a sensible, easy-to-read range (roughly single or low-double digits up to a few thousand).
Examples
A car's mass → kilograms (not grams — too many digits). A dose of medicine → millilitres (not litres — the number would be a tiny, awkward decimal like 0.005). A pencil's length → centimetres (not metres or km).
✓ Quick Check 2 — Harder Conversions & Choosing Units
Question 1 of 10
Interactive Metric Converter
Use this tool to explore any metric conversion. It shows you both the result and the operation used — great for checking your working.
Metric Unit Converter
✓ Quick Check 3 — Real-Life Contexts
Question 1 of 10
Practice: Metric Unit Conversions
Enter your answers as numbers.
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Question
Answer
Result
1
Convert 3.5 km to m
2
Convert 250 cm to m
3
Convert 4.2 kg to g
4
Convert 1,500 ml to litres
5
Convert 0.75 m to cm
6
Convert 2.4 m to cm
7
Convert 850 mm to m
8
Convert 12 kg to g
9
Convert 3,000 ml to litres
10
Convert 0.6 km to m
11
Convert 6 km to metres
12
Convert 2500 g to kilograms
13
Convert 4.7 litres to millilitres
14
Convert 320 cm to metres
15
Convert 0.85 km to metres
16
Convert 75 mm to centimetres
17
Convert 1.25 kg to grams
18
A bottle holds 1.5 litres. How many millilitres is this?
⚠ Things to Watch Out For
When converting, decide whether to multiply or divide — multiplying when going to a smaller unit, dividing when going to a larger one.
Make sure you use the correct conversion factor for the units involved (e.g. 1 km = 1000 m, not 100 m).
Don't mix units in a calculation — convert everything to the same unit first.
Take care with litres and millilitres: 1 litre = 1000 ml, not 100 ml.
For area and volume, remember to square or cube the conversion factor (e.g. 1 m² = 10 000 cm², not 100 cm²).