Converters for everyday units
Most conversions are one multiplication, but the right factor, the right unit and the right rounding are easy to get wrong. The converters below start from sensible defaults, show the factor behind every answer and list the same value in the other common units.
- Centimetres to Inches Converter – Centimetres to inches (and back) with a table and exact formula.
- Inches to mm Converter – Inches to millimetres and back, with nearest-fraction output.
- Feet to Inches Converter – Feet to inches (and back) with yards, metres and a table.
- Feet to Metres Converter – Feet to metres (and back), using the exact 0.3048 factor.
- Kilometres to Miles Converter – Kilometres to miles and back, with race distances and a table.
- CM to Feet and Inches Converter – Height in cm to feet and inches, with a height chart.
- Metres to Yards Converter – Metres to yards and back, with sports distances.
- Acres to Square Feet Converter – Acres to square feet, hectares and m², with a lot-size table.
- Square Feet to Square Metres Converter – Square feet to square metres (and back), with room examples.
- Gallons to Litres Converter – US and UK gallons to litres and back, with quarts and ounces.
- ML to Ounces Converter – Millilitres to US or UK fluid ounces, with cups and litres.
- Cubic Feet to Gallons Converter – Cubic feet to US gallons, litres, m³ and cubic yards.
- Kilograms to Pounds Converter – Kilograms to pounds (and back), with ounces, grams and stone.
- Grams to Ounces Converter – Grams to ounces (and back), with pounds and kilograms.
- Tons to Pounds Converter – US, UK and metric tons to pounds and kilograms.
- Stone to Pounds Converter – Stone to pounds and kg, or kg to stone and pounds.
- Celsius to Fahrenheit Converter – Celsius to Fahrenheit (and back), with kelvin and a chart.
- Km/h to MPH Converter – Km/h to mph and back, with m/s, knots and a speed-limit chart.
- Knots to MPH Converter – Knots to mph, km/h and m/s, for boats, aircraft and wind.
- PSI to Bar Converter – PSI to bar, kPa, atm and mmHg, with a tyre pressure chart.
- Horsepower to Kilowatts Converter – Horsepower to kilowatts, watts and BTU/h, with metric PS.
- Hours to Minutes Converter – Hours to minutes (and back), with decimal hours and h:mm:ss.
- Degrees to Radians Converter – Degrees to radians (and back), with gradians, turns and π table.
- Amps to Watts Calculator – Amps to watts (and watts to amps) for DC, AC and three-phase.
- Unit Converter – One converter for length, area, volume, weight, temperature, speed and more.
Which converter do I need?
For lengths and heights, start with cm to inches, inches to mm, feet to inches and cm to feet and inches, or feet to metres, metres to yards and km to miles for larger distances. For areas, use square feet to square metres and acres to square feet. For liquids and tanks, use gallons to litres, ml to ounces and cubic feet to gallons.
For weights, try kg to pounds, grams to ounces, stone to pounds and tons to pounds. For everything else, use the unit converter, or the dedicated tools for temperature, speed, pressure, horsepower, time and angles. The amps to watts calculator handles electrical power.
Exact definitions
Since 1959 the inch, foot, yard and mile have been defined from the metre, so conversions between customary and metric lengths are exact. The pound is exactly 0.45359237 kg, and the US gallon is exactly 231 cubic inches. The US survey foot, which differed by about two parts per million, was retired after 2022.
Tips for accurate conversions
Check which unit variant you have, because tons, gallons and ounces each have more than one meaning. Keep full precision until the final step, then round to the precision of your measurement. When you convert prices, quantities or doses, convert the units first and compare afterwards.
Frequently asked questions
Are these converters free?
Yes. Every converter on CalcTen is free to use with no sign-up. The site is supported by advertising.
How accurate are the conversion factors?
Factors are exact definitions or values published by NIST, such as 1 inch = 25.4 mm, 1 pound = 0.45359237 kg and 1 US gallon = 3.785411784 L. Results are rounded to eight significant digits.
Why are there separate pages for pairs like cm to inches and inches to mm?
Each page is set up for how people use that pair, with the right default units, a table of common values, worked examples and answers to the questions that come up most. Every page can also convert in the other direction.
What is the difference between US and UK units?
Length and weight units match, but liquid volumes differ. A US gallon is 3.785 L and a UK gallon is 4.546 L, and a US fluid ounce is 29.57 mL against 28.41 mL in the UK. A US ton is 2,000 lb and a UK ton is 2,240 lb.
Can I convert cooking measurements?
Volume conversions such as ml to ounces work for liquids. Cup-to-gram conversions depend on the ingredient, so they are not a single factor.
Can I rely on these for safety-critical work?
Use them as a check, not as the only source. For medicine doses, engineering, aviation or navigation, confirm results with an authoritative source or a qualified professional.