Select a category using the category pills (Length, Weight, Temperature, etc.), then choose your "From" and "To" units from the dropdowns. Type a value in either field and the converted result appears instantly. Use the swap button to reverse the direction. You can also use the formula bar to see the exact conversion formula being applied.
Divide centimetres by 2.54 to get inches. For example: 30 cm ÷ 2.54 = 11.81 inches. To go the other way, multiply inches by 2.54: 12 inches × 2.54 = 30.48 cm. One inch equals exactly 2.54 centimetres by international definition since 1959. Common reference points: 1 cm ≈ 0.39 inches; 1 foot = 30.48 cm; 1 metre = 39.37 inches.
Multiply kilograms by 2.20462 to get pounds. For example: 70 kg × 2.20462 = 154.32 lbs. To convert pounds to kilograms, divide by 2.20462: 150 lbs ÷ 2.20462 = 68.04 kg. Quick approximation: 1 kg ≈ 2.2 lbs. For stone (used in the UK for body weight): 1 stone = 6.35 kg = 14 lbs.
Use the formula: °F = (°C × 9/5) + 32. For example: 25°C = (25 × 1.8) + 32 = 77°F. To reverse: °C = (°F − 32) × 5/9. Key reference points to memorise: 0°C = 32°F (water freezes), 20°C = 68°F (room temperature), 37°C = 98.6°F (body temperature), 100°C = 212°F (water boils). To convert Celsius to Kelvin, simply add 273.15.
Multiply miles by 1.60934 to get kilometres. To convert km to miles, multiply by 0.62137. Handy reference: 5 miles ≈ 8 km; 10 miles ≈ 16.1 km; 26.2 miles (marathon) = 42.2 km. Speed conversions follow the same ratio: 60 mph = 96.6 km/h; 100 km/h = 62.1 mph.
The metric system (SI) uses base-10 units — metres, kilograms, litres, and Celsius — and is used by the vast majority of the world including all of Europe, Asia, Africa, and most of the Americas. The imperial system uses feet, pounds, gallons, and Fahrenheit — still common in the United States. The UK uses a mix: metric for most official purposes but miles for road distances and pints for beer. Scientific work worldwide uses metric exclusively.
Length: 1 inch = 2.54 cm · 1 foot = 0.305 m · 1 mile = 1.609 km · 1 nautical mile = 1.852 km
Weight: 1 lb = 453.6 g · 1 kg = 2.205 lbs · 1 stone = 6.35 kg · 1 oz = 28.35 g
Volume: 1 US gallon = 3.785 L · 1 UK gallon = 4.546 L · 1 cup = 236.6 mL · 1 fl oz = 29.57 mL
Area: 1 acre = 4047 m² · 1 sq mile = 2.59 km² · 1 hectare = 10,000 m²
Speed: 1 mph = 1.609 km/h · 1 knot = 1.852 km/h
Digital: 1 GB = 1024 MB · 1 TB = 1024 GB
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