Unit Converter
It converts values between metric and imperial units across length, mass, volume, area, speed, temperature and digital data.
Centimeter → Inch
39.3701
Millimeter
1,000.0000
Meter
1.0000
Kilometer
0.0010
Inch
39.3701
Foot
3.2808
Yard
1.0936
What it calculates
It converts values between metric and imperial units across length, mass, volume, area, speed, temperature and digital data.
Why it matters
Mixed-unit work causes expensive mistakes, from recipes to engineering specifications.
Who it's for
Students, engineers, cooks, travellers and developers working across measurement systems.
Formula
- Factor
- Ratio between source and target unit
- Offset
- Additional shift used by temperature scales
Worked example
12 miles to kilometers
- 11 mile = 1.609344 km exactly
- 212 × 1.609344 = 19.312128
12 miles is 19.312 kilometers
How the unit converter works
Most conversions are a single multiplication by an exact factor. Temperature is the exception: it needs a scale factor and an offset, because the zero points differ.
Every unit is stored as a factor relative to its SI base unit, so conversions run through a single exact multiplication and division without accumulating rounding error.
Temperature is handled separately because Celsius, Fahrenheit and Kelvin have different zero points as well as different scales.
Common mistakes
- Mixing US and imperial gallons, which differ by about 20%.
- Confusing mass (kg) with force (N) or weight.
- Treating 1 kB as 1024 bytes when the context means 1000.
Tips and best practice
- Keep full precision through intermediate steps and round only at the end.
- Sanity-check the direction — a value in km should be larger than the same distance in miles.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
°F = °C × 9/5 + 32. The converter handles the offset automatically.
How many kilometers in a mile?
Exactly 1.609344 kilometers — the mile was defined against the meter in 1959, so the figure is exact rather than rounded. Twelve miles is 19.312 km.
Is a US gallon the same as a UK gallon?
No. A US gallon is 3.785 liters; an imperial gallon is 4.546 liters.
Why do US and imperial gallons differ?
They were standardized separately. A US gallon is 3.785 liters and an imperial gallon is 4.546 — about 20% larger, which matters a great deal for fuel economy figures.
What is the difference between a gigabyte and a gibibyte?
A gigabyte is 10⁹ bytes; a gibibyte is 2³⁰, or 1,073,741,824 bytes. Drive manufacturers use gigabytes while operating systems often report gibibytes, which is why a 1 TB drive shows as about 931 GB.
Why is temperature handled separately?
Every other conversion is a single multiplication, but temperature scales have different zero points, so they need an offset as well as a scale factor.
Related calculators
Methodology & trust
- Formula source
- SI definitions and NIST conversion factors.
- Last updated
- 2026-07-28
- Privacy
- Every calculation runs in your browser. No inputs are sent to a server or stored.
- Accessibility
- Keyboard navigable, labeled inputs and WCAG AA color contrast.