Convertix

Convertix is a Unit Converter
Convertix is Free.
It is easy-to-use. Simply select a unit and the amount to convert and you will obtain the equivalences with the rest of the compatible Units.
Convertix has more than 30 different Units Classes, such as Length, Volume, Angles, etc.
Also, if the Unit Class you need doesn't or it exists but with a lower detail, you can enter a new (own) Unit Class and use it freely.
There are two different conversion methods to enter your own Unit Classes:
By ratio. The most common conversion method. It is used to convert form one unit to another by a simply number o ratio, for example 1 kilometer is equal to 1,000 meters.
By formula. It is used when the equivalence between two units is not a ratio but a function, for example conversion between Degree Celsius and Degree Farenheit: °C=(°F-32)*5/9.
Convertix lets you to enter up to two new Units Classes.
It is also available Convertix+, the paid version with no limitation to create new Unit Classes.
Convertix is available in English and Spanish.