Conversion factors used
1 km = 0.621371 miles. 1 cm = 0.393701 inches. 1 kg = 2.204623 pounds. °F = (°C × 9/5) + 32, and °C = (°F − 32) × 5/9.
Quick reference tables
| Length | Metric | Imperial |
|---|---|---|
| 1 km | 0.62 miles | |
| 1 m | 3.28 feet | |
| 30 cm | 11.8 inches | |
| 2.54 cm | 1 inch |
| Weight | Metric | Imperial |
|---|---|---|
| 1 kg | 2.2 lb | |
| 0.45 kg | 1 lb | |
| 1,000 kg | 2,205 lb |
| Temperature | Celsius | Fahrenheit |
|---|---|---|
| Water freezes | 0°C | 32°F |
| Room temperature | 20–22°C | 68–72°F |
| Body temperature | 37°C | 98.6°F |
| Water boils | 100°C | 212°F |
Why metric and imperial still coexist
Most of the world standardized on the metric system through the 19th and 20th centuries because it's decimal-based — everything scales by factors of 10, which makes conversion between units (millimeters to meters to kilometers) simple arithmetic. The United States remains a notable exception for everyday use, still relying on inches, feet, pounds, and Fahrenheit despite metric being the standard in science, medicine, and most manufacturing even domestically. The UK uses a mix of both depending on context — miles for road distances, but metric for most other measurements.
A note on precision
The conversion factors above are accurate to 6 decimal places, which is more than enough for everyday use, cooking, travel, or fitness tracking. For scientific or engineering work requiring higher precision, official standards bodies (such as NIST in the US) publish exact defined conversion constants — 1 inch is exactly 2.54 cm by international agreement since 1959, for instance.
Frequently asked questions
Why do the US and UK still use imperial units?
Most of the world switched to the metric system because it's decimal-based and simpler to convert between units. The US kept imperial units for everyday use, while the UK uses a mix of both depending on context.
How accurate are these conversions?
The conversion factors used are accurate to 6 decimal places, which is precise enough for everyday, travel, cooking, and fitness use.