Unit Converter
Convert length, mass, volume, and temperature using exact SI and US customary factors, with the substitution steps a student would write on paper.
5 km = 3.10685596119 mi
- Convert to the SI base (meters): 5 × 1000 = 5000 m.
- Convert from meters to mi: 5000 / 1609.344 = 3.10685596119 mi.
- Equivalent factor: 1 km = 0.621371192237 mi.
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All calculations run locally in your browser. Your entered values are not sent to an external service.
How to Use the Unit Converter
Select a category, enter the value you have, choose the unit it is in and the unit you want, then select Convert. The tool shows the converted value, the factor it used, and the SI (or Celsius) amount in between.
- Choose Length, Mass, Volume, or Temperature.
- Enter the number and the from and to units.
- Select Convert, or use Swap to reverse the units.
Length, mass, and volume use exact international factors: 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, and 1 US gallon = 3.785411784 L. Volume cups and gallons here are the US customary sizes, not imperial UK measures. For imperial gallons, cubic inches, and a longer kitchen list, use the Volume Converter.
The Conversion Method
Every length, mass, or volume unit is defined as a fixed multiple of an SI base: meters, kilograms, or liters. Convert the input into that base, then divide by the target unit’s base factor. The same steps work in either direction, and converting a unit to itself leaves the value unchanged.
Temperature is not a scale that starts at zero in every system, so it cannot use a single multiply. Convert to Celsius first, then apply F = C × 9/5 + 32 or K = C + 273.15. Temperatures below 0 K are rejected as physically undefined.
Unit Converter Examples
Five kilometers to miles
5 km = 5000 m. One mile is 1609.344 m, so 5000 ÷ 1609.344 = 3.10685596119 mi. A common rounded classroom value is 3.11 miles, but the international mile is exactly 1.609344 km, not 1.6 km.
A person’s height in centimeters
72 inches × 2.54 cm per inch = 182.88 cm. Because the inch is defined as exactly 25.4 mm, this result is exact, not an approximation.
Pounds to kilograms
The international pound is exactly 0.45359237 kg, so 2.5 lb = 1.133980925 kg. Kitchen scales that treat 1 kg as 2.2 lb are using a rounded factor (the more precise value is about 2.20462 lb per kg).
One US gallon to liters
A US liquid gallon is 231 cubic inches, which is exactly 3.785411784 L. An imperial gallon is larger (about 4.546 L), so recipes and fuel economy figures must name which gallon they use.
The same unit
5 m to 5 m is a useful check: when the units match, the converter must return the original value and skip a spurious factor.
Why Temperature Uses a Formula, Not a Factor
0 °C is the freezing point of water, not “no temperature.” Fahrenheit places that same point at 32 °F, and Kelvin places absolute zero at 0 K, which is −273.15 °C. Multiplying 100 by 9/5 gives 180, not 212 — you must add 32. The converter always goes through Celsius so the offset is applied once, in the right place.
100 °C = 212 °F and 0 °C = 32 °F. 373.15 K is 100 °C, the boiling point of water at standard pressure. This page does not convert cooking gas marks, wind chill, or heat index.
Common Unit Mistakes
Treating 1 mile as exactly 1.6 kilometers
1 mile = 1.609344 km exactly. 1.6 km is a rounding that accumulates on long distances.
Forgetting the +32 in Celsius to Fahrenheit
The size of one degree is 9/5, but the zeros of the scales do not line up. Always add or subtract 32 after scaling.
Mixing US and imperial gallons
This tool uses the US liquid gallon. Imperial gallons and US dry gallons are different sizes.
Confusing mass with volume
A liter of water is about one kilogram only near 4 °C. Oil, flour, and air do not convert that way, so mass and volume stay separate here.
Entering a temperature below 0 K
Absolute zero is the lower bound. The converter rejects inputs that would imply a negative kelvin value.
Unit Converter FAQs
How do you convert from one unit to another?
Change the value into an SI base unit, then into the target unit. For temperature, convert through Celsius and apply the offset.
How many miles is 5 kilometers?
5 km = 3.10685596119 miles, because 1 mile is exactly 1609.344 meters.
How do you convert Celsius to Fahrenheit?
Multiply by 9/5, then add 32. So 100 °C becomes 180 + 32 = 212 °F.
Is 1 inch exactly 2.54 centimeters?
Yes. The international inch has been defined as exactly 25.4 mm since 1959.
Does this convert currency, time zones, or cooking by weight?
No. It converts length, mass, volume, and temperature only. Percent change belongs on the Percent Calculator.
Are my numbers sent to a server?
No. The calculation runs locally in your browser.
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Reviewed by Prof. Dr. Khalil Mudassar (PhD) · Last updated: [mc_modified_date]
Sources
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Disclaimer
This converter is for general educational use. It uses international and US customary definitions and does not replace a legal-for-trade scale, a laboratory instrument, or professional engineering conversion tables.