A converter for every unit system
The world uses two major measurement systems. The metric system — officially the International System of Units (SI) — is based on multiples of ten and serves as the reference in almost every country. The imperial system, with its US variants, is still used daily in the United States and, for some measures, in the United Kingdom: inches, feet, miles, gallons, pounds and degrees Fahrenheit are the norm there. Whenever you read an Anglo-Saxon recipe, follow an American DIY plan or check the specifications of an imported product, a conversion becomes necessary.
This converter covers the most useful categories: lengths, areas, volumes, masses, temperatures, energies and angles. You choose the category, the starting unit and the target unit, then the result appears as soon as you enter a value. The units in each category are grouped to avoid confusion — there is no risk of accidentally converting fluid ounces into weight ounces.
Common conversions worth knowing
A few benchmarks are worth memorising. For lengths: one inch is exactly 2.54 centimetres, one foot is 30.48 centimetres and one mile is 1.609 kilometres. For masses: one pound is about 454 grams and one ounce is 28.35 grams. For US volumes: one US gallon holds 3.785 litres (compared with 4.546 litres for the British imperial gallon, a difference that really matters in cooking and mechanics).
Temperature is a special case because the conversion is not proportional: it combines a scale factor and an offset. The formula is °C = (°F − 32) × 5/9. Thus 68 °F, a typical room temperature in American instructions, equals 20 °C, and the boiling point of water, 212 °F, is exactly 100 °C. The converter applies this formula automatically, including for negative temperatures where mental arithmetic errors are common.
Precision and rounding
The conversion factors used are official definitions: the inch has been exactly 25.4 millimetres since the 1959 international agreement, and the kilogram, metre and degree Celsius follow the SI definitions revised in 2019. The displayed result is rounded for readability; for professional use — machining, pharmacy, construction — apply the result with the precision required by your field and check applicable tolerances.
Frequently asked questions about unit conversion
What is the difference between the US gallon and the British gallon?
The US gallon is 3.785 litres, the British imperial gallon is 4.546 litres, about 20 % more. The same confusion exists for pints and fluid ounces. Always check the origin of a recipe or instruction before converting a volume.
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9: °C = (°F − 32) × 5/9. For example, 100 °F gives (100 − 32) × 5/9 ≈ 37.8 °C. The converter applies this formula directly, with no intermediate calculation on your part.
Are the results exact or approximate?
The conversion factors are exact official definitions (1 inch = 2.54 cm, 1 pound = 0.45359237 kg). Only the display is rounded for readability. The precision of your result therefore depends mainly on the precision of the value you enter.
Why does France use the metric system?
The metric system was created in France during the Revolution, with the metre defined in 1791, then gradually adopted worldwide. It is now the basis of the International System of Units (SI), used by the science, industry and commerce of almost every country.
Can I convert computer units with this tool?
This converter covers physical units: lengths, areas, volumes, masses, temperatures, energies and angles. Computer units (bytes, kilobytes, megabytes) follow different conventions — binary or decimal — and are not included in the categories offered.