Unit Conversion
Metric units multiply or divide by 10, 100, or 1000. Follow the chain — never skip steps.
A. Length
Length Conversion Chain
Kilometre (km) to Metre (m)
1 km = 1000 m. To convert km → m: multiply by 1000. To convert m → km: divide by 1000.
Example
3.5 km → m: 3.5 × 1000 = 3500 m
2500 m → km: 2500 ÷ 1000 = 2.5 km
2500 m → km: 2500 ÷ 1000 = 2.5 km
Metre (m) to Centimetre (cm)
1 m = 100 cm. To convert m → cm: multiply by 100.
Example
4.2 m → cm: 4.2 × 100 = 420 cm
350 cm → m: 350 ÷ 100 = 3.5 m
350 cm → m: 350 ÷ 100 = 3.5 m
Inch, Foot, Yard, Mile
Imperial units still tested in MCQs.
Key values
1 inch = 2.54 cm
1 foot = 12 inches = 30.48 cm
1 yard = 3 feet = 0.914 m
1 mile = 1.609 km
1 foot = 12 inches = 30.48 cm
1 yard = 3 feet = 0.914 m
1 mile = 1.609 km
Example 1 — Convert 5.4 km to cm
1km → m: 5.4 × 1000 = 5400 m
2m → cm: 5400 × 100 = 540000 cm
5.4 km = 540,000 cm
Example 2 — Convert 3 feet to cm
11 foot = 30.48 cm
23 feet = 3 × 30.48 = 91.44 cm
3 feet = 91.44 cm
B. Mass & Weight
Mass Conversion Chain
Tonne → Kilogram → Gram
1 tonne = 1000 kg. 1 kg = 1000 g. 1 g = 1000 mg.
Example
2.5 kg → g: 2.5 × 1000 = 2500 g
3000 mg → g: 3000 ÷ 1000 = 3 g
3000 mg → g: 3000 ÷ 1000 = 3 g
Imperial Mass
1 pound (lb) = 0.4536 kg. 1 ounce (oz) = 28.35 g.
Example5 lb = 5 × 0.4536 = 2.268 kg
Example — Convert 3.2 tonnes to grams
1tonnes → kg: 3.2 × 1000 = 3200 kg
2kg → g: 3200 × 1000 = 3,200,000 g
3.2 tonnes = 3,200,000 g
C. Volume & Capacity
Litre (L) and Millilitre (mL)
1 litre = 1000 mL. 1 mL = 1 cm³. 1 m³ = 1000 litres.
Example
2.5 L → mL: 2.5 × 1000 = 2500 mL
750 mL → L: 750 ÷ 1000 = 0.75 L
750 mL → L: 750 ÷ 1000 = 0.75 L
Gallon
1 gallon = 3.785 litres (used in some MCQs).
Example4 gallons = 4 × 3.785 = 15.14 litres
⚠ Common mistakes:
(1) Skipping steps — when converting km to cm, go km→m→cm in two steps. Do not try to do it in one jump.
(2) Dividing instead of multiplying — going from a small unit to a large one means dividing. Going from large to small means multiplying.
(3) Ratio to % error — always divide each part by the total of all parts, not just the other part.
D. Ratio ↔ Percentage Conversion
Ratio to Percentage
Divide each part by the total, then multiply by 100.
Example — ratio 3:7
Total = 3 + 7 = 10
3/10 × 100 = 30% and 7/10 × 100 = 70%
3/10 × 100 = 30% and 7/10 × 100 = 70%
Percentage to Ratio
Write both percentages over 100, simplify, then write as a ratio.
Example — 40% and 60%
40:60 → divide by 20 → 2:3
Example — Rs.5400 split in ratio 2:3:4. What % does each get?
1Total parts = 9. As %, each part = (part/9) × 100
22/9 × 100 = 22.2% 3/9 × 100 = 33.3% 4/9 × 100 = 44.4%
22.2% : 33.3% : 44.4% (total ≈ 100%)
⚡ MCQ Tip: The three most tested conversions are 1 km = 1000 m, 1 kg = 1000 g, and 1 L = 1000 mL. For multi-step conversions (e.g. km to cm) always go step by step — never try to jump in one calculation.
Quick MCQ Revision
| Conversion | Value |
|---|---|
1 km | = 1000 m |
1 m | = 100 cm = 1000 mm |
1 kg | = 1000 g |
1 tonne | = 1000 kg |
1 litre | = 1000 mL = 1000 cm³ |
1 inch | = 2.54 cm |
1 foot | = 12 inches = 30.48 cm |
1 mile | = 1.609 km |