Unit Converter: Metric & US

A unit converter that is exact where exactness exists - and says so where it does not.

Almost every conversion between defined units is exact by definition. An inch is exactly 25.4 mm. A pound is exactly 0.45359237 kg. A US gallon is exactly 3.785411784 litres. Most converters turn those definitions into decimal approximations and then show you twelve digits of the result, and the last few of them are the app's own rounding error rather than your answer.

This one keeps every value as an exact fraction from the moment you type it to the moment it is drawn. Convert 5 km to miles and back and you get exactly 5 km, every time, however many times you do it.


★ TEMPERATURE IS TWO DIFFERENT QUESTIONS
• 20 °C is 68 °F. But a RISE of 20 °C is a rise of 36 °F - and almost every converter answers only the first while you are asking the second
• Switch between "a temperature" and "a difference", and the screen always tells you which one you are looking at
• That is the difference between the oven at 180 and turning the oven up by 20, and it is 32 degrees wide


★ THE ANSWER IS AS PRECISE AS YOUR QUESTION
• Type 2 cups and get 473.2 mL, not 473.176473
• Type 2.00000000 cups and get 473.176473, because now you asked for it
• Set how few figures is too few; the app never shows fewer, and never shows more than you asked for
• Tap Exact value for the answer as a fraction, plus whether its decimal ever ends


★ NINE FAMILIES, DONE PROPERLY
• Length, weight, temperature, volume, area, speed, time, data and pressure - 112 units
• Both data ladders, labelled: a gigabyte is 10^9 bytes and a gibibyte is 2^30, which is why a 1 TB drive shows 931 of something
• US and imperial kept apart, because a US pint is 473 mL and a British one is 568
• The US survey foot, exactly 1200/3937 m - a fraction whose decimal never ends, so no ordinary converter holds it
• Units that depend on a convention say so: a light-year needs a definition of "year", and a Mach number needs an air temperature


★ IT COLLAPSES TO WHAT YOU USE
• Star the units you actually convert and they come to the top
• Recent pairs sit under the converter as one-tap shortcuts, and a pin keeps one for good
• Search by name or symbol - kg, sq ft, °F - and by either spelling, metre or meter
• Reads numbers from any keyboard, including Persian, Devanagari and fullwidth digits


★ YOURS, AND ON YOUR PHONE
• Works completely offline - every unit and every conversion factor is inside the app, so airplane mode changes nothing
• No account, no sign-up, no cloud, nothing uploaded
• Three permissions, all three for ads: internet, network state, advertising ID. No storage permission, no notifications, nothing running in the background
• Your favourites are excluded from Android cloud backup on purpose, so they are never copied to a Google account


★ ADS
No banner ads anywhere. There is a full-screen ad occasionally, and only after you copy or share a result - never while you are typing, never on a unit, and never in front of the exact value. An optional video turns ads off for a day.