One converter for the conversions daily life actually throws at you: this tool covers eight categories — length, weight, temperature, speed, area, volume, data, and energy — using exact international definitions, and shows the formula behind every result.
How It Works
Every category except temperature converts through a base unit. Each unit carries a factor (its size in the base unit), and conversion is:
Lengths normalize to metres (1 inch = exactly 0.0254 m; 1 mile = 1,609.344 m), weights to kilograms (1 lb = exactly 0.45359237 kg), areas to square metres (1 acre = 4,046.8564224 m²), volumes to litres, speeds to km/h (1 knot = 1.852 km/h exactly), energy to joules (1 kcal = 4,184 J; 1 kWh = 3.6 MJ), and data to bytes. Results are rounded to eight decimal places, fine enough that rounding never costs you a meaningful digit. Temperature is the exception — it converts through Celsius with its offset (see the dedicated temperature converter for the full treatment).
| Category | Units included | | --- | --- | | Length | mm, cm, m, km, inch, foot, yard, mile, nautical mile | | Weight | mg, g, kg, tonne, ounce, pound, stone | | Speed | km/h, mph, m/s, ft/s, knot | | Area | sq cm, sq m, sq km, hectare, acre, sq foot, sq inch, sq mile | | Volume | ml, litre, cubic metre, US gallon, UK gallon, US cup, fluid oz, tablespoon, teaspoon | | Data | bit, byte, KB, MB, GB, TB, KiB, MiB | | Energy | joule, kilojoule, calorie, kilocalorie, watt-hour, kWh, BTU |
Worked Examples
- The marathon: 26.219 miles × 1,609.344 ÷ 1,000 = 42.195 km — the official distance, recovered exactly.
- Highway speeds: 100 km/h ÷ 1.609344 = 62.14 mph — why a European 100 limit feels like an American 62.
- Storage reality check: a 1 GB file (1,000,000,000 bytes) is 953.67 MiB — the root of every "missing" hard-drive capacity argument, covered below.
The Traps This Converter Helps You Avoid
US vs UK gallons differ by 20%. A US gallon is 3.785 litres; an imperial (UK) gallon is 4.546 litres. Fuel economy, recipes, and aquarium volumes all silently break when the wrong gallon sneaks in — this tool keeps them as separate units because they are separate units. (The volume set is US-measure for cups, tablespoons, and teaspoons as well.)
Data units: decimal vs binary. Storage manufacturers sell decimal: 1 KB = 1,000 bytes, 1 GB = 10⁹ bytes — the definitions this tool uses for KB/MB/GB/TB. Operating systems often report binary units (KiB = 1,024 bytes, MiB = 1,048,576 bytes), which are included here alongside. A "1 TB" drive holding 10¹² bytes is about 931 GiB of binary capacity; nothing is missing — the labels differ. Note the binary ladder here climbs to MiB; for GiB/TiB conversions, chain through bytes.
Stone persists in UK body weight: 1 stone = 14 lb = 6.350 kg, included for exactly the people who need it. And speed's m/s is the scientist's unit: multiply by 3.6 for km/h, the conversion this tool's factors encode directly.
Frequently Asked Questions
Why does temperature not use a simple factor like the others?
Because its scales have different zero points, not just different step sizes: 0 °C is not "no temperature," so conversion needs an offset as well as a ratio (°F = °C × 9/5 + 32). Every other category here shares a true zero, which is what makes the single-factor method exact.
Which gallon should I use?
US gallons for American recipes, fuel, and products; UK (imperial) gallons for older British specifications and a few Commonwealth contexts. Modern UK fuel is sold in litres, so the imperial gallon mostly survives in legacy documents — when a source does not say, geography is your clue.
How accurate are the results?
The factors are the exact international definitions (the inch, pound, acre, and knot are all defined exactly in metric terms), and results carry eight decimal places. Any error in a converted figure will come from the measurement you started with, not from the conversion.