Imperial units — such as inches, feet, pounds and pints — don't scale in powers of 10 like metric units do, so their conversion relationships must be memorised rather than worked out. They are often given in the exam, but knowing them by heart saves time and builds confidence.
1 inch ≈ 2.54 cm 1 foot ≈ 30.48 cm 1 mile ≈ 1.6 km
Mass
16 ounces (oz) = 1 pound (lb) 14 pounds = 1 stone 8 stone = 1 hundredweight
1 oz ≈ 28 g 1 kg ≈ 2.2 lb 1 stone ≈ 6.35 kg
Capacity
8 pints = 1 gallon
1 pint ≈ 568 ml 1 gallon ≈ 4.5 litres
⚠ Imperial conversions are not powers of 10. You must know each relationship individually — they cannot be worked out by moving decimal places.
✓ Quick Check 1 — Imperial Unit Relationships
Question 1 of 10
Converting Between Imperial Units
Example 1: Convert 5 feet 3 inches to inches.
1
5 × 12 = 60 inches (from the feet)
2
Total = 60 + 3 = 63 inches
Example 2: A person weighs 11 stone 6 pounds. Convert to pounds.
1
11 × 14 = 154 lb (from the stones)
2
Total = 154 + 6 = 160 lb
Example 3: Convert 3.5 gallons to pints.
1
3.5 × 8 = 28 pints
✓ Quick Check 2 — Stones, Pounds, Yards & Gallons
Question 1 of 10
Converting Imperial to Metric (and back)
To convert imperial → metric, multiply by the conversion factor. To convert metric → imperial, divide by the conversion factor. (More worked examples and practice: Lesson 11.3 — Metric and Imperial Conversions.)
💡 Trick to remember the direction: Miles → km? Multiply by 1.6 (km are smaller, so you need more of them). Km → miles? Divide by 1.6.
Worked Example: A journey is 12 miles. How many km is this?
Step 1 — Identify direction
Imperial (miles) → Metric (km): multiply by the conversion factor.