Measurement conversions

Why convert?

Measurements must be in the same units before you can compare or combine them. A recipe in mL, a jug in L, a map in km and a plan in cm all need conversion.

Metric conversions

The metric system is based on 10s. Each metric prefix has a fixed size:

Moving down the chart (to smaller units): multiply by 10 for each step. Moving up: divide.

• 4.2 km → m: 3 steps down → × 1,000 = 4,200 m
• 3,500 mg → g: 3 steps up → ÷ 1,000 = 3.5 g
• 65 cm → m: ÷ 100 = 0.65 m

Conversion factors

A conversion factor is a fraction equal to 1, like 100 cm/1 m. Multiply so the unwanted unit cancels.

Example: 2.5 m → cm

2.5 m × (100 cm / 1 m) = 250 cm

Area: square the factor

1 m = 100 cm, so 1 m² = 100 cm × 100 cm = 10,000 cm².

Example: 3 m² = 30,000 cm².

Volume: cube the factor

1 m³ = 100 × 100 × 100 = 1,000,000 cm³.

Handy links: 1 cm³ = 1 mL; 1,000 cm³ = 1 L; 1 m³ = 1,000 L.

Metric and imperial

Example: 6 ft 2 in → cm. 74 in × 2.54 = 188 cm (rounded).

Time

60 s = 1 min; 60 min = 1 h; 24 h = 1 day. 2.5 h = 150 min.

Worked examples

Example 1: 0.75 L → mL: × 1,000 = 750 mL.

Example 2: 45,000 cm² → m²: ÷ 10,000 = 4.5 m².

Example 3: 10 km → miles: 10 ÷ 1.609 ≈ 6.2 miles.

Common mistakes

• Multiplying when you should divide. Smaller units → bigger number.
• Using 100 for area conversions between m² and cm² (it’s 10,000).
• Forgetting to convert all measurements to the same unit before calculating.

Try it yourself

1. 7.3 m to mm
2. 2,450 g to kg
3. 2 m² to cm²
4. 5,000 cm³ to L
5. 12 inches to cm

Answers: 1) 7,300 mm 2) 2.45 kg 3) 20,000 cm² 4) 5 L 5) 30.48 cm

Quick recap

• Use metric prefixes: multiply going smaller, divide going larger.
• Square units use the factor squared; cubic units use it cubed.
• Use conversion factors to cancel units cleanly.