Free online unit converter for length, weight, temperature, area, volume, speed, and data storage. Convert between metric and imperial units instantly — feet to meters, Fahrenheit to Celsius, pounds to kilograms, gallons to liters, and 100+ more conversions.
Metric • Imperial • 7 categories
The United States is one of only three countries in the world — alongside Myanmar and Liberia — that has not officially adopted the metric system as its primary measurement standard. While the US Metric Conversion Act of 1975 declared the metric system the "preferred system" for US trade and commerce, everyday American life is dominated by imperial units: feet and miles for distance, pounds and ounces for weight, Fahrenheit for temperature, and gallons for volume. This creates a constant practical need for unit conversion, especially for international travel, science, cooking, construction, and commerce.
The most commonly searched unit conversions by Americans include: feet to meters (1 foot = 0.3048 meters), miles to kilometers (1 mile = 1.60934 km), Fahrenheit to Celsius (subtract 32, multiply by 5/9), pounds to kilograms (1 lb = 0.453592 kg), and gallons to liters (1 US gallon = 3.78541 liters). A quick mental shortcut for Celsius/Fahrenheit: double the Celsius temperature and add 30 for a rough Fahrenheit estimate (works best in the 0–30°C range). For exact values, use this calculator.
Temperature conversion is the most conceptually confusing because it requires both multiplication and addition, not just a simple ratio. The three temperature scales in common use are: Fahrenheit (F) used in the US for everyday weather, Celsius (C) used in science and most of the world, and Kelvin (K) used in physics where 0 K is absolute zero. Water freezes at 32°F = 0°C = 273.15 K, and boils at 212°F = 100°C = 373.15 K. Normal human body temperature is 98.6°F = 37°C.
In cooking, unit conversion is essential when using international recipes. European and UK recipes typically use metric measurements (grams, milliliters) while American recipes use cups, tablespoons, and ounces. Key cooking conversions: 1 cup = 236.6 mL. 1 tablespoon = 14.79 mL = 3 teaspoons. 1 fluid ounce = 29.57 mL. 1 pound flour ≈ 3.5 cups. Note that volume-to-weight conversions for cooking depend on the ingredient — a cup of flour weighs about 120g while a cup of sugar weighs about 200g.
Data storage units have become increasingly important in the digital age. The modern data hierarchy: 1 byte = 8 bits. 1 kilobyte (KB) = 1,024 bytes. 1 megabyte (MB) = 1,024 KB. 1 gigabyte (GB) = 1,024 MB. 1 terabyte (TB) = 1,024 GB. Note the ongoing confusion between decimal (1 KB = 1,000 bytes, used by hard drive manufacturers and internet speeds) and binary (1 KiB = 1,024 bytes, used by operating systems). This calculator uses binary (IEC standard) for data storage conversions.
Only 3 countries don't use metric: USA, Myanmar, Liberia. US officially designated metric as "preferred" in 1975 but never mandated it. Science, medicine, military, and international trade in the US use metric. Everyday life uses imperial.
Freezing: 32°F = 0°C. Body temp: 98.6°F = 37°C. Boiling: 212°F = 100°C. Room temp: ~72°F = 22°C. Hot summer day: 95°F = 35°C. Formula: °C = (°F−32) × 5/9
1 cup = 236.6 mL. 1 tbsp = 14.79 mL. 1 tsp = 4.93 mL. 1 fl oz = 29.57 mL. 1 lb = 453.6g. 1 stick butter = 113g = ½ cup = 8 tbsp. 1 US gallon = 3.785 L.
1 GB = 1,024 MB. 1 TB = 1,024 GB. A photo ≈ 3–5 MB. A song ≈ 4–8 MB (MP3). HD movie ≈ 4–8 GB. 4K movie ≈ 60–100 GB. 1 TB drive holds ≈ 250,000 photos or 250 HD movies.
A general unit converter works by routing every value through a base unit for its quantity: multiply into the base, then divide out of it. That two-step approach is what allows one engine to handle length, mass, volume and dozens of other quantities without storing a conversion factor for every possible pair — for n units you need n factors rather than n² pairs. The discipline that matters is dimensional consistency: you can convert metres to feet because both measure length, but not metres to kilograms, and a converter that permits the latter is producing nonsense.
value_in_base = value × factor_fromresult = value_in_base ÷ factor_toCombined: result = value × (factor_from ÷ factor_to)Both units must share the same dimensionwhere:
Assumptions: Temperature is the exception: Celsius and Fahrenheit have different zero points, so they need an offset as well as a factor and cannot use the pure multiplicative route.
SourceNIST: SI units
Route a conversion through metres rather than using a direct foot-to-centimetre factor.
Result12 feet = 365.76 centimetres
The economy of the base-unit approach is the point: storing 20 length factors supports 380 possible conversions. Storing pairs directly would need all 380 entries, and any error in one would be invisible until that specific pair was used.