📋 In this guide
Whether you are filling a form that asks for height in centimetres, checking a recipe in Fahrenheit, or comparing weights in kilograms and pounds, a wrong conversion can quietly spoil the result. This guide gives you the most useful conversions in one place, with formulas and worked examples you can verify yourself.
1. Length Conversions
Length is the unit most people convert daily — height, distance, screen size or land measurement. Metric units move by powers of 10, while metric-to-imperial conversions use fixed factors.
| From | To | Factor |
|---|---|---|
| 1 inch | Centimetres | 2.54 (exact) |
| 1 foot | Centimetres | 30.48 (exact) |
| 1 metre | Feet | 3.28084 |
| 1 kilometre | Miles | 0.621371 |
| 1 mile | Kilometres | 1.609344 |
| 1 kilometre | Metres | 1,000 |
5 ft 8 in = (5 × 12) + 8 = 68 inches → 68 × 2.54 = 172.72 cm.
2. Weight Conversions
Weight (strictly, mass) matters for body weight, luggage limits, shipping and cooking. Kilograms and pounds are the two you will meet most often.
| From | To | Factor |
|---|---|---|
| 1 kilogram | Pounds | 2.20462 |
| 1 pound | Kilograms | 0.453592 |
| 1 ounce | Grams | 28.3495 |
| 1 quintal | Kilograms | 100 |
| 1 tonne | Kilograms | 1,000 |
70 × 2.20462 = 154.32 lb (rounded to two decimals).
3. Temperature Conversions
Temperature is different from length and weight because the scales start at different zero points. You cannot just multiply — you must also add or subtract an offset.
| Celsius | Fahrenheit | Meaning |
|---|---|---|
| 0°C | 32°F | Water freezes |
| 25°C | 77°F | Comfortable room temperature |
| 37°C | 98.6°F | Normal body temperature |
| 100°C | 212°F | Water boils (at sea level) |
(98.6 − 32) × 5/9 = 66.6 × 5/9 = 37°C.
4. Decimal-Point Mistakes to Avoid
- Shifting the decimal the wrong way. 1 km = 1,000 m, so 2.5 km is 2,500 m — not 25 m.
- Mixing up multiply and divide. Going to a smaller unit (m → cm) gives a bigger number; going to a larger unit (cm → m) gives a smaller number.
- Rounding too early. Keep at least 4–5 decimal places during the calculation and round only the final answer.
- Ignoring the offset in temperature. Multiplying °C by 1.8 alone is incomplete; always add 32.
- Confusing feet-inches with decimal feet. 5 ft 6 in is 5.5 ft, not 5.6 ft.
Frequently Asked Questions
How many centimetres are in one inch?
One inch is exactly 2.54 centimetres.
How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 1.8 and add 32. For example, 37°C = 37 × 1.8 + 32 = 98.6°F.
How many pounds are in one kilogram?
One kilogram is about 2.20462 pounds.
Why do I get a wrong answer when converting units?
The usual causes are moving the decimal point by the wrong number of places, mixing up multiply and divide, and rounding too early.
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