Unit Converter

What Is Unit Conversion?

Unit conversion is the process of expressing a measured quantity in a different unit without changing the quantity itself — turning 5 kilometers into 3.1069 miles, or 100°C into 212°F. Most conversions work by relating each unit to a common base: for length the base is the meter, for weight the kilogram, for volume the liter, and so on. To convert from one unit to another you scale the value into the base unit using the source unit’s factor, then scale out of the base using the target unit’s factor. Temperature is the exception, since its scales have different zero points, and fuel economy is another: liters per 100 km and miles per gallon are inversely related, so one goes up when the other goes down.

Because measurement systems grew up independently around the world, the same physical thing is described by metric units in most countries and by imperial or US customary units elsewhere. Reliable conversion bridges that gap, whether you are reading a foreign recipe, following an engineering spec, checking tire pressure, comparing car fuel consumption, or interpreting a weather report.

How to Use This Unit Converter

The quickest way is the Type a conversion box: write what you want in plain words, such as 5 ft 10 in to cm, 72 F to C, 1 1/2 cups in ml, 100 km/h to mph or 30 mpg to l/100km. The converter picks the category and units for you. Mixed units like feet and inches, pounds and ounces, or hours and minutes are added together. If you only type a quantity (12 stone), it is converted into a sensible default unit.

You can also pick a category, type a value into the left box and choose both units from the dropdowns. Both boxes are editable: type into the right box and the left one updates, so you can convert in either direction without swapping. The ⇄ button swaps the units. Below the boxes you see the result in words, the conversion factor in both directions (for temperature and fuel economy, the formula), and — for feet, inches, pounds and stone — the result split the way people usually say it, for example “5 ft 10.87 in”.

The grid shows your value in every unit of the category; tap any cell to make it the target unit. Copy link to this conversion gives you a URL such as /unit-converter/?cat=length&from=km&to=mi&v=5 that opens the converter with the same values. Numbers can be typed with thousands separators (1,500), a decimal comma (2,5), as fractions (1/2, 1 1/2) or in scientific notation (3e8).

Common Conversion Factors

These factors are exact by definition unless marked ≈. The converter uses the same values internally.

From	To	Multiply by
1 inch	centimeters	2.54
1 foot	meters	0.3048
1 mile	kilometers	1.609344
1 kilometer	miles	≈ 0.621371
1 pound	kilograms	0.45359237
1 kilogram	pounds	≈ 2.204623
1 ounce	grams	28.349523125
1 stone	pounds	14
1 US gallon	liters	3.785411784
1 UK (imperial) gallon	liters	4.54609
1 US cup	milliliters	236.5882365
1 acre	square meters	4,046.8564224
1 mph	km/h	1.609344
1 psi	bar	≈ 0.0689476
1 kcal (food Calorie)	kilojoules	4.184
1 mechanical horsepower	kilowatts	≈ 0.7457

Temperature uses formulas instead of factors: °F = °C × 9/5 + 32, °C = (°F − 32) × 5/9 and K = °C + 273.15. For fuel economy, L/100 km = 235.215 ÷ mpg (US) and L/100 km = 282.481 ÷ mpg (UK).

Real-World Use Cases

• Height and body weight — 180 cm is 5 ft 10.87 in; 70 kg is 154.32 lb or 11 st 0.32 lb.
• Cooking and baking — convert cups, tablespoons, teaspoons and fluid ounces to milliliters, and oven temperatures between °C and °F.
• Cars and travel — km/h and mph, tire pressure in psi and bar, fuel economy in mpg and L/100 km, engine power in kW, hp and PS.
• Home and DIY — inches to centimeters, square feet to square meters, cubic feet to liters.
• Science and engineering — kelvin, pascals, joules, watt-hours, radians, hertz and rpm.

Tips for Accurate Conversions

• US or UK? Cups, pints, quarts, gallons and fluid ounces differ between the US and the UK. A UK gallon is about 20% larger than a US gallon, so UK mpg figures look higher for the same car. Both versions are available.
• Which “ton”? A metric ton (tonne) is 1,000 kg, a US short ton 907.18 kg and a UK long ton 1,016.05 kg. Typing ton means the US short ton; use tonne or t for the metric one.
• Calories: the “Calories” on food labels are kilocalories (kcal). 1 kcal = 4.184 kJ.
• Months and years in the time category are fixed lengths (30 and 365 days). For calendar-exact spans between two dates, use the Date Calculator.

Features

• 13 categories — length, weight, temperature, area, volume, speed, time, pressure, energy, power, fuel economy, angle and frequency.
• Plain-text input — “5 ft 10 in to cm”, “72°F in C”, “1 1/2 cups to ml”.
• Two-way editing — type into either box.
• Exact factors — the internationally defined values, not rounded approximations.
• Factor and formula shown — so you can check the result or do it by hand next time.
• Feet + inches, pounds + ounces, stone + pounds shown automatically.
• Shareable links — every conversion has its own URL.
• 100% client-side — nothing you type leaves your browser.

Frequently Asked Questions

How accurate are the conversions?

The converter uses the exact definitions — for example 1 inch = 2.54 cm, 1 pound = 0.45359237 kg and 1 US gallon = 3.785411784 liters — and computes in double-precision floating point. Results are shown with up to 10 significant digits, which is more precision than any everyday measurement has.

How many centimeters are in an inch, and inches in a foot?

One inch is exactly 2.54 centimeters, and one foot is 12 inches, or 30.48 centimeters. To convert a height such as 5 ft 10 in, type 5 ft 10 in to cm: the result is 177.8 cm.

How do I convert Celsius to Fahrenheit?

Multiply by 9/5 and add 32: 20 °C × 1.8 + 32 = 68 °F. The other way, subtract 32 and multiply by 5/9. −40 is the one temperature that is the same on both scales. The converter warns you if a value is below absolute zero (−273.15 °C or −459.67 °F).

How do I convert mpg to L/100 km?

Divide 235.215 by the US mpg figure (or 282.481 by the UK mpg figure). 30 mpg (US) is about 7.84 L/100 km. Because the relationship is inverse, you cannot use a simple multiplier — a car that uses more fuel has a higher L/100 km but a lower mpg.

Are the cup, pint and gallon US or UK measures?

Both are available. The units marked “US” use US customary measures (1 cup = 236.59 ml, 1 gallon = 3.785 L); the units marked “UK” use imperial measures (1 pint = 568.26 ml, 1 gallon = 4.546 L). Typing gallon or pint means the US unit; type uk gallon or imperial pint for the British one.

How long are a “month” and a “year” in the time category?

They are fixed approximations: a month is 30 days and a year is 365 days. They are convenient for rough estimates but do not account for varying month lengths or leap years.

Does this converter work offline and keep my data private?

Yes. All calculations run in JavaScript inside your browser, so nothing you enter is sent to a server. Once the page has loaded, the converter keeps working without an internet connection.