Supported Systems Overview¶
This reference page provides a complete catalog of all systems of quantities and units available in mp-units. For detailed explanations of system architecture and how they work, see System Definitions in the User's Guide.
All Available Systems¶
The following table lists all systems available in the library. The "Documented" column indicates systems with detailed User's Guide documentation.
| System | Quantities | Units | Description & Use Cases | Documented |
|---|---|---|---|---|
| ISQ | ✓ | International System of Quantities (from ISO/IEC 80000 series) - foundation for SI and other systems. Use when you need the full typed quantity hierarchy. | ✓ | |
| SI | ✓ | International System of Units - modern metric system, most widely used. Best for most engineering and scientific applications as the international standard. | ✓ | |
| CGS | ✓ | Centimetre-Gram-Second system - still used in some areas of physics and chemistry. Use when interfacing with legacy physics code or specific scientific domains. | ✓ | |
| Yard-Pound | ✓ | Base units system from the 1959 international yard and pound agreement. Foundation for Imperial and USC systems. Use directly when you need the common base units without regional extensions. | ✓ | |
| Imperial | ✓ | British Imperial system extending yard-pound with UK-specific units (stone, imperial gallon, long ton). Use when required by UK industry standards or regulations. | ✓ | |
| USC | ✓ | United States customary units extending yard-pound with US-specific units (US gallon, survey units, Fahrenheit). Use for aviation, construction, and other industries in the US. | ✓ | |
angular |
✓ | ✓ | Standalone strong angular system with dimensional angle and units. Use for rotational mechanics when you want explicit angle dimensions without the full ISQ hierarchy. | ✓ |
isq_angle |
✓ | ISQ amendment incorporating strong angular quantities. Use when you need both the ISQ quantity hierarchy and strong angular dimensions (e.g., for physically-correct torque units). | ✓ | |
| Natural | ✓ | ✓ | High-energy physics system where fundamental constants (\(c\), \(\hbar\), \(k_B\)) equal unity. Use for particle physics and cosmology calculations. | ✓ |
| IAU | ✓ | International Astronomical Union standardized constants from official resolutions: nominal solar/planetary values (Resolution B3), astronomical unit (Resolution B2), CODATA 2018 gravitational constant and masses. Use for professional astronomy/astrophysics requiring IAU-standardized values. | ✓ | |
| Astronomy | ✓ | Common astronomy utility units not standardized by IAU: light-year, lunar distance, jansky, sidereal day, Julian/tropical year, century, millennium, gaussian gravitational constant. Use for general astronomy calculations. | ||
| IEC | ✓ | IEC-standardized units including electrical (var), telecommunications (erlang, baud), and information technology (bit, byte). Use for electrical engineering and IT applications. | ||
| Typographic | ✓ | Typography and desktop publishing units: US/DTP points and picas, Didot point and cicero (European), Q and H (Japanese), TeX point. Use for font design, typesetting, and publishing applications. | ||
| HEP | ✓ | High-energy physics units: electronvolt (energy), barn (cross-section), fermi (femtometre), particle masses (electron, proton, neutron), atomic mass unit, fundamental constants (c, h, ℏ, e). Use for particle physics experiments and calculations. |
Note
The checkmarks show what each system defines. Systems of units are always built upon systems of quantities, so including a system of units (like SI) also provides access to the quantities it depends on (though SI only imports the ISQ quantities needed for its definitions, not the entire ISQ system).
System Headers¶
Each system can be included via its corresponding header:
#include <mp-units/systems/angular.h> // Strong Angular System (standalone)
#include <mp-units/systems/astronomy.h> // Common astronomy utility units
#include <mp-units/systems/cgs.h> // Centimetre-Gram-Second
#include <mp-units/systems/hep.h> // High-energy physics units
#include <mp-units/systems/iau.h> // IAU standardized astronomical constants
#include <mp-units/systems/iec80000.h> // IEC information units
#include <mp-units/systems/imperial.h> // British Imperial units
#include <mp-units/systems/isq.h> // International System of Quantities
#include <mp-units/systems/isq_angle.h> // Strong Angular System (ISQ amendment)
#include <mp-units/systems/natural.h> // Natural Units
#include <mp-units/systems/si.h> // International System of Units
#include <mp-units/systems/typographic.h> // Typographic units
#include <mp-units/systems/usc.h> // US Customary units
#include <mp-units/systems/yard_pound.h> // Yard-Pound base units (1959 international agreement)
For detailed information about each documented system, its quantities, units, and usage patterns, refer to the individual system pages linked in the table above.