Unit Converter
Convert length, mass, volume, and temperature.
Converted value
- From
- 1 mi
- To
- 1.609344 km
Miles (mi) → Kilometers (km).
How the unit converter works
For length, mass, and volume, every unit is defined as an exact multiple of one base unit: meters for length, kilograms for mass, and liters for volume. To convert, the tool first scales your value into the base unit, then scales the base unit into the target. In one step that is out = value * (factorFrom / factorTo), where each factor is the unit’s exact size in the base unit. Because the factors are the official definitions (for example 1 inch = 0.0254 m, 1 pound = 0.45359237 kg), the math is exact and reversible.
Temperature is different. The scales have different zero points, not just different sizes, so a plain multiply would be wrong. The tool converts through a Celsius hub using affine formulas: F = C * 9/5 + 32, C = (F - 32) * 5/9, K = C + 273.15, and C = K - 273.15. This is why 0 C is 32 F, not 0 F.
Worked example
Convert 5 miles to kilometers.
- Factor for miles: 1 mi = 1609.344 m
- Factor for kilometers: 1 km = 1000 m
- Compute:
5 * (1609.344 / 1000) = 5 * 1.609344 - Result: 8.04672 km
Now a temperature: convert 25 C to Fahrenheit and Kelvin.
| Target | Formula | Result |
|---|---|---|
| Fahrenheit | 25 * 9/5 + 32 |
77 F |
| Kelvin | 25 + 273.15 |
298.15 K |
Both results are exact, not rounded, because the underlying factors and offsets are exact.
How to use it
- Pick the category first (length, mass, volume, or temperature). You can only convert within a single category.
- Choose the from and to units, enter a number, and read the result. Negative numbers are valid for temperature and will convert correctly.
- Use the exact unit you mean. Volume uses US customary cups, pints, quarts, and gallons. Mass includes the stone (st = 6.35029318 kg) for UK body-weight figures.
- Reverse a conversion by swapping the from and to units. The result will return to your original value because the factors are exact inverses.
- For very large or very small magnitudes, prefer scientific notation in your input rather than typing long strings of zeros, which reduces typing errors.
Limitations
This tool converts between units of the same physical quantity only. It cannot turn mass into volume or back, because that depends on the density of a specific material (water, flour, and oil all differ), which the converter does not store. Volume units are US customary, so they will not match imperial UK measures, and “fluid ounce” here is a volume, not a weight. Temperature conversion does not block physically impossible inputs such as values below absolute zero, so sanity-check any unusual figure yourself. The output is a precise mathematical conversion, but it does not account for measurement error in the original value you entered.
Frequently asked questions
Why are pound and ounce conversions not round numbers?
The converter uses the internationally defined exact values: 1 pound equals 0.45359237 kg and 1 ounce equals 0.028349523125 kg. These are the legal definitions, so a result like 1 ounce = 0.028349523125 kg reflects the true factor rather than a rounded approximation.
Does it use US or imperial gallons?
It uses the US liquid gallon, defined as exactly 3.785411784 liters. The imperial gallon (about 4.546 liters) is larger, so values entered as 'gal' here will not match UK fuel or recipe figures.
Can I convert from miles directly to feet, or kg directly to ounces?
Yes. Within a category, any unit converts to any other unit because every conversion routes through a shared base unit (meters, kilograms, or liters). You are not limited to neighboring units.
Why can't I convert kilograms to liters?
Mass and volume measure different physical quantities, so there is no fixed factor between them. The relationship depends on the density of the specific substance, which this tool does not model. Convert only within one category.
Is 0 Kelvin or a negative temperature handled correctly?
Yes. Temperature uses affine formulas with offsets, not simple scaling, so 0 K converts to -273.15 C and -40 C returns exactly -40 F. The tool does not block physically unusual values, so it will convert below absolute zero if you enter such a number.