Universal Unit Converter
High-precision measurement transformations for laboratory, workshop, and kitchen environments.
Systems of Measurement
Most of the world uses the International System of Units (SI), commonly known as the Metric system. It is base-10, making it easier for scientific calculations. The U.S. Customary System (Inches, Pounds) is used primarily in the United States and originated from British Imperial units.
Laboratory Accuracy
Precision matters. This tool uses 4-decimal float precision. In technical work, always remember:
- Weight vs. Mass: Weight is gravity-dependent; Mass is constant.
- Kelvin: Used in physics, Kelvin starts at "Absolute Zero" (-273.15°C).
- Volume: 1ml of water is equal to exactly 1 gram (at sea level).
Common Pitfalls
The most common error in measurement is confusing Fluid Ounces (volume) with Ounces (weight). 8 fl oz of lead and 8 fl oz of feathers take up the same space, but their weight is drastically different. Our tool separates these categories to prevent calculation errors.
Converting between measurement systems
Convert length, weight, volume, area and temperature between metric and imperial units. The conversions here use exact internationally agreed factors rather than the rounded approximations that accumulate error across several steps.
Factors worth remembering
One inch is exactly 25.4 millimetres, which is a definition rather than a measurement. A mile is 1.609 kilometres, a pound is 0.4536 kilograms, and a US gallon is 3.785 litres.
Temperature is the odd one out because the scales have different zero points. Celsius to Fahrenheit means multiplying by 1.8 and adding 32, not simply scaling. Minus 40 is the one temperature where both scales agree.
Where conversions go wrong
US and imperial gallons are different. A US gallon is 3.785 litres and an imperial gallon is 4.546, a difference of around 20 percent. The same split affects pints and fluid ounces, which is why British and American recipes disagree.
Weight and volume are not interchangeable in cooking. A cup of flour weighs about 120 grams and a cup of sugar about 200, so converting a volume measure to grams requires knowing the ingredient. Serious baking recipes give weights for exactly this reason.
Ounces are ambiguous. A fluid ounce measures volume and an ounce measures mass, and they are only loosely related for water. Check which one a recipe means before converting.
A note on precision
Convert once, at the end, rather than at each step. Rounding repeatedly compounds error, and a measurement is only as precise as its least precise input. Reporting a converted figure to six decimal places implies an accuracy the original never had.
US and imperial differ
Gallons, pints and fluid ounces are all different sizes in the two systems. Check which one your source uses.
Weigh your baking
Volume measures for flour vary by 20 percent depending on how the cup was filled. Scales solve it.
Minus 40
The only point where Celsius and Fahrenheit read the same number. A useful sanity check.
Frequently asked questions
Are US and imperial gallons the same?
No. A US gallon is 3.785 litres and an imperial gallon is 4.546. Pints and fluid ounces differ the same way.
How do I convert a cup of flour to grams?
It depends on the ingredient. Flour is roughly 120 grams per cup, sugar about 200. Volume to weight needs a density figure.
What is the formula for Celsius to Fahrenheit?
Multiply by 1.8 and add 32. To reverse it, subtract 32 and divide by 1.8.
Why do small rounding differences appear?
Most conversion factors are irrational or very long decimals. Convert once at the end rather than at each intermediate step.