Unit conversion

Edexcel papers test unit conversion in pure form ("convert 3.4 km to cm") and in real-world contexts (speed, density, currency). On Higher, conversions of compound units (m/s ↔ km/h, g/cm³ ↔ kg/m³) appear frequently.

Length

• 10 mm = 1 cm
• 100 cm = 1 m
• 1000 m = 1 km
• 1 mile ≈ 1.609 km (or use 5 miles ≈ 8 km for non-calc estimation)
• 1 inch = 2.54 cm

Mass

• 1000 mg = 1 g
• 1000 g = 1 kg
• 1000 kg = 1 tonne (metric)
• 1 lb ≈ 0.454 kg (or 1 kg ≈ 2.2 lb)

Capacity / volume

• 1000 mL = 1 L
• 1 cm³ = 1 mL
• 1000 cm³ = 1 L
• 1 m³ = 1000 L = 1,000,000 cm³

Time

• 60 seconds = 1 minute
• 60 minutes = 1 hour
• 24 hours = 1 day
• 365 (or 366) days = 1 year

Currency (Edexcel real-life context)

• £ ↔ € via given exchange rate (e.g. £1 = €1.15).
• For "best buy" questions, convert to the same currency before comparing.

Compound unit conversion

Speed: m/s ↔ km/h.

• m/s × 3.6 = km/h. (because 1000 m / 3600 s = 1/3.6).
• km/h ÷ 3.6 = m/s.
• Worked example: 25 m/s = 25 × 3.6 = 90 km/h.

Density: g/cm³ ↔ kg/m³.

• 1 g/cm³ = 1000 kg/m³.
• Worked example: 7.8 g/cm³ × 1000 = 7800 kg/m³ (steel).

Pressure: N/cm² ↔ N/m².

• 1 cm² = 0.0001 m², so 1 N/cm² = 10,000 N/m².

Edexcel exam tip

For compound unit conversions, always convert each component separately. m/s → km/h: convert m to km (÷ 1000), s to h (× 3600), then combine. Never multiply both terms by the same factor — units don't work that way.