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Unit Conversion Guide: Lengths, Weights, Temperatures, and More
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Unit conversions come up in cooking, construction, science, travel, and online shopping. This guide covers the most-used conversions with the exact formulas, plus quick approximations for mental math.
Length
Exact conversions:
• 1 inch = 2.54 cm
• 1 foot = 30.48 cm = 0.3048 m
• 1 yard = 0.9144 m
• 1 mile = 1.60934 km
• 1 kilometer = 0.62137 miles
Quick approximations:
• cm → inches: divide by 2.5 (exact: ÷2.54)
• km → miles: multiply by 0.6 (exact: ×0.621)
• meters → feet: multiply by 3.28
Weight and Mass
Exact conversions:
• 1 ounce = 28.3495 g
• 1 pound = 453.592 g = 0.453592 kg
• 1 kilogram = 2.20462 lbs
• 1 stone (UK) = 14 pounds = 6.35 kg
• 1 US ton = 2,000 lbs = 907 kg
• 1 metric tonne = 1,000 kg = 2,204.6 lbs
Quick approximations:
• kg → lbs: multiply by 2.2
• lbs → kg: divide by 2.2
Temperature
Formulas (exact):
• °C to °F: (°C × 9/5) + 32
• °F to °C: (°F − 32) × 5/9
• °C to K: °C + 273.15
Key reference points:
• 0°C = 32°F (water freezes)
• 100°C = 212°F (water boils)
• 37°C = 98.6°F (body temperature)
• 20°C = 68°F (comfortable room temperature)
Quick approximation: double the Celsius temperature and add 30 for a rough Fahrenheit equivalent.
Volume
Liquid volume:
• 1 US fluid ounce = 29.574 mL
• 1 US cup = 236.588 mL
• 1 US pint = 473.176 mL
• 1 US gallon = 3.785 L
• 1 UK (Imperial) gallon = 4.546 L
Note: US and UK pints and gallons are different. 1 UK pint = 568 mL; 1 US pint = 473 mL.
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Frequently Asked Questions
Why do the US and UK use different measurement systems?
The US retained a version of the pre-metric English system after independence. The UK officially adopted the metric system but retains some imperial measures in everyday use (miles for road distances, pints for beer in pubs, etc.).
Is the metric system always better?
The metric system's base-10 structure makes calculations easier and reduces errors in science, medicine, and engineering. For everyday informal use, either system works fine if you are familiar with it.