Imperial Unit Conversions

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Imperial Unit Relationships

Imperial units do not use powers of 10 — you must memorise the relationships below. These are often given in the exam but are worth knowing.

Quantity	Imperial Relationships	Metric Approximation
Length	12 inches = 1 foot 3 feet = 1 yard 1,760 yards = 1 mile	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.

5 × 12 = 60 inches (from the feet)

Total = 60 + 3 = 63 inches

Example 2: A person weighs 11 stone 6 pounds. Convert to pounds.

11 × 14 = 154 lb (from the stones)

Total = 154 + 6 = 160 lb

Example 3: Convert 3.5 gallons to pints.

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.

Step 2 — Apply factor

1 mile ≈ 1.6 km: \(12 \times 1.6 = \mathbf{19.2\text{ km}}\)

Worked Example: A recipe uses 900 g of flour. How many ounces is this? (metric → imperial)

Step 1 — Identify direction

Metric (g) → Imperial (oz): this time we're going the other way, so divide by the conversion factor (1 oz ≈ 28 g).

Step 2 — Apply factor

\(900 \div 28 = \mathbf{32.1\text{ oz}}\) (to 1 d.p.)

Imperial Unit Converter

Enter a value, select the unit to convert from, and see the metric result instantly.

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From (imperial)

✓ Quick Check 3 — Real-Life Imperial Problems

Question 1 of 10

Practice: Imperial Unit Conversions

Enter your answers as numbers, using the relationships table above.

#	Question	Answer	Result
1	Convert 3 feet to inches
2	Convert 5 miles to yards
3	Convert 4 stone to pounds
4	Convert 32 ounces to pounds
5	Convert 3 gallons to pints
6	Convert 6 feet to inches
7	Convert 2 miles to yards
8	Convert 10 stone to pounds
9	Convert 48 ounces to pounds
10	Convert 5 gallons to pints

⚠ Things to Watch Out For

Miles and kilometres are often confused — remember 5 miles ≈ 8 km, so 1 mile is more than 1 km.
Pounds and kilograms: 1 kg ≈ 2.2 lbs, so a kilogram is heavier than a pound.
Inches and centimetres: 1 inch = 2.54 cm — don't mix these up with the feet-to-metres conversion.
Pints and litres: 1 litre ≈ 1.75 pints — a litre is less than 2 pints, not more.
Always use the conversion factor given in the question — don't rely on approximate values you've memorised if a different one is provided.

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Imperial Unit Conversions

Learning Objectives

Real-World Applications

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Example 1: Convert 5 feet 3 inches to inches.

Example 2: A person weighs 11 stone 6 pounds. Convert to pounds.

Example 3: Convert 3.5 gallons to pints.

Imperial Unit Converter

Practice: Imperial Unit Conversions

⚠ Things to Watch Out For