Unit conversion is one of the most universally needed skills — from cooking and travel to engineering and science. Yet it's surprisingly easy to get wrong. This guide covers every major unit type, explains the formulas, and links to free instant converters for each category.
1. Metric vs Imperial Systems
The two dominant measurement systems in the world are Metric (SI) and Imperial. Understanding the difference is the foundation of all unit conversion.
The Metric System
Used by 95% of the world's population, the metric system is built on base-10. Every unit scales by powers of 10 — milli (÷1000), centi (÷100), kilo (×1000), mega (×1,000,000). This makes calculations straightforward:
- Length: millimetre → centimetre → metre → kilometre
- Weight: milligram → gram → kilogram → tonne
- Volume: millilitre → litre → kilolitre
The Imperial System
Used primarily in the United States (and partially in the UK and Canada), the imperial system has irregular scaling — 12 inches in a foot, 3 feet in a yard, 1760 yards in a mile. This makes mental math harder:
- Length: inch → foot (×12) → yard (×3) → mile (×1760 yards)
- Weight: ounce → pound (×16) → stone (×14 lb) → ton (×2000 lb)
- Volume: teaspoon → tablespoon (×3) → cup (×16 tbsp) → gallon (×16 cups)
India officially uses the metric system, but imperial units still appear in real estate (square feet), body weight discussions (kg vs lbs), and imported goods. Understanding both is essential.
2. Length & Distance
Length is the most commonly converted unit type — heights, distances, screen sizes, fabric, construction measurements.
Key Conversion Factors
| From | To | Multiply by |
|---|---|---|
| 1 inch (in) | centimetres | 2.54 |
| 1 foot (ft) | centimetres | 30.48 |
| 1 metre (m) | feet | 3.28084 |
| 1 kilometre (km) | miles | 0.621371 |
| 1 mile (mi) | kilometres | 1.60934 |
| 1 yard (yd) | metres | 0.9144 |
Most Searched Length Conversions
- cm to feet — height measurement worldwide
- feet to cm — reverse height conversion
- km to miles — road distances, running distances
- miles to km — US to metric distance
- metres to feet — altitude, property dimensions
- inches to cm — screen size, clothing measurements
📏 Length Converter
Convert between mm, cm, m, km, in, ft, yd, mi and 20+ more units instantly.
Open Length Converter →3. Weight & Mass
Weight conversion is essential for health tracking, shipping, cooking, and gym use. The kilogram (kg) is the SI base unit; the pound (lb) is the most common imperial unit.
Key Conversion Factors
| From | To | Multiply by |
|---|---|---|
| 1 kilogram (kg) | pounds | 2.20462 |
| 1 pound (lb) | kilograms | 0.453592 |
| 1 kilogram (kg) | grams | 1000 |
| 1 ounce (oz) | grams | 28.3495 |
| 1 stone (st) | kilograms | 6.35029 |
| 1 tonne | kilograms | 1000 |
Quick Mental Math
For kg to lbs: multiply by 2.2 (accurate to within 0.3%). For example, 75 kg × 2.2 = 165 lbs.
For lbs to kg: divide by 2.2. For example, 150 lbs ÷ 2.2 = 68.2 kg.
- kg to lbs — body weight, gym weights
- lbs to kg — reverse conversion
- grams to ounces — cooking ingredients
- ounces to grams — US recipes in metric
4. Temperature
Temperature conversion is needed for weather, cooking, medicine, and science. The three main scales are Celsius (°C), Fahrenheit (°F), and Kelvin (K).
Formulas
°C = (°F − 32) × 5/9
K = °C + 273.15
Key Reference Points
| Celsius | Fahrenheit | What it means |
|---|---|---|
| 0°C | 32°F | Freezing point of water |
| 20°C | 68°F | Comfortable room temperature |
| 37°C | 98.6°F | Normal human body temperature |
| 100°C | 212°F | Boiling point of water |
Quick Mental Trick
To roughly convert °C to °F: double the Celsius value and add 30. For example, 25°C × 2 + 30 = 80°F (exact: 77°F). Accurate within 5°F.
- °C to °F — weather, cooking
- °F to °C — US to metric
- °C to Kelvin — science, chemistry
🌡️ Temperature Converter
Convert between Celsius, Fahrenheit, Kelvin and Rankine.
Open Temperature Converter →5. Area
Area conversions are critical for real estate, land measurement, agriculture, and construction. India uses a mix of metric (m², km²), traditional (bigha, guntha, cent, ground), and international (acre, hectare) units.
Key Conversion Factors
| From | To | Value |
|---|---|---|
| 1 acre | m² | 4,046.86 m² |
| 1 hectare | acres | 2.47105 acres |
| 1 sq ft | m² | 0.0929 m² |
| 1 bigha (UP) | sq ft | 27,000 sq ft |
| 1 ground | sq ft | 2,400 sq ft |
| 1 cent | sq ft | 435.6 sq ft |
Note: Indian traditional units like bigha, guntha, and ground vary by state. Always confirm the local definition when dealing with land transactions.
→ Open Area Converter (includes bigha, guntha, ground, cent, marla)6. Volume & Capacity
Volume is critical for cooking, medicine, fuel, and industrial use. The litre (L) is the most common everyday unit; millilitres (ml) for medicine and cooking; gallons for fuel in the US.
Key Conversion Factors
| From | To | Multiply by |
|---|---|---|
| 1 litre (L) | US gallons | 0.264172 |
| 1 US gallon | litres | 3.78541 |
| 1 cup (US) | millilitres | 236.588 |
| 1 tablespoon | millilitres | 14.787 |
| 1 teaspoon | millilitres | 4.929 |
| 1 fluid ounce | millilitres | 29.5735 |
For cooking conversions (cups, tbsp, tsp, ml), use the dedicated Cooking Converter.
🧪 Volume Converter
Convert between L, ml, gallon, cup, pint, fl oz and more.
Open Volume Converter → Cooking Converter →7. Speed
Speed conversions matter for road travel, aviation, sports, and physics. The most common conversion globally is between km/h and mph.
km/h = mph × 1.60934
Quick tip: to convert km/h to mph, multiply by 0.6 (rough). For example, 100 km/h × 0.6 = 60 mph (exact: 62.1 mph).
- km/h to mph — road speed
- mph to km/h — US speed to metric
8. Digital Storage
Data storage units are essential for understanding file sizes, storage devices, and internet speeds. Everything scales by 1024 (or 1000 in SI):
| Unit | Bytes | Example |
|---|---|---|
| 1 Kilobyte (KB) | 1,024 B | A short text email |
| 1 Megabyte (MB) | 1,048,576 B | A high-quality photo |
| 1 Gigabyte (GB) | ~1.07 billion B | A HD movie |
| 1 Terabyte (TB) | ~1.1 trillion B | A laptop hard drive |
9. All 51 Converter Categories
Unitafy covers every unit type you'll encounter. Browse all categories: