The Boost.Units library is a C++ implementation of dimensional analysis in a general and extensible manner, treating it as a generic compile-time metaprogramming problem. With appropriate compiler optimization, no runtime execution cost is introduced, facilitating the use of this library to provide dimension checking in performance-critical code. Support for units and quantities (defined as a unit and associated value) for arbitrary unit system models and arbitrary value types is provided, as is a fine-grained general facility for unit conversions. Complete SI and CGS unit systems are provided, along with systems for angles measured in degrees, radians, gradians, and revolutions and systems for temperatures measured in Kelvin, degrees Celsius and degrees Fahrenheit. The library architecture has been designed with flexibility and extensibility in mind; demonstrations of the ease of adding new units and unit conversions are provided in the examples.

In order to enable complex compile-time dimensional analysis calculations with no runtime overhead, Boost.Units relies heavily on the Boost Metaprogramming Library (MPL) and on template metaprogramming techniques, and is, as a consequence, fairly demanding of compiler compliance to ISO standards. At present, it has been successfully compiled and tested on the following compilers/platforms :

The following compilers/platforms are known not to work :