Facilitates working with physical quantities.

This is a work in progress; this package's API may change significantly.
Some parts are currently unfinished, untested and/or undocumented. Use at your own risk.

Quick start

// Import the core library
import 'package:quantity/quantity_si.dart';

// Construct an Angle in radians
var ang = new Angle(rad: 1.1);

// Construct an Angle in degrees
var ang2 = new Angle(deg: 270);

// Find the difference
var diff = ang2 - ang;

// Display the result in degrees

Key Features

  • Typed quantities (such as Length, Mass and Temperature) that are easy to construct and use in calculations.
  • Encourages use of standard units by isolating non-standard units in an extension library.
  • Support for relative standard uncertainty in quantity values and calculations.
  • Allows use of arbitrary precision values (as well as complex and imaginary values).
  • Provides access to the latest official constant values published by NIST.
  • Integration with Dart's existing Duration and DateTime classes.
  • Extensive set of quantity types and standard and non-standard units.
  • Support for untyped quantities having unusual dimensions with the MiscQuantity class.
  • Models quantity ranges, including special support for angle ranges and time spans.
  • Includes a mutable quantity with streams.
  • Metric prefixes for any unit.


Quantity types, units and constants commonly encountered in the field of Astronomy and related sciences.
Quantity types, units and constants commonly encountered in the fields dealing with electromagnetics.
The quantity package accepts both Dart's num types and the Numbers defined by this number library as quantity values and for quantity operations. [...]
A superset of all the other libraries available in the quantity package. [...]
Extends the core library with non-SI units, constants, unit synonyms to enable terse constructors and expressions, and auxiliary functions.
Models ranges of quantities with start and end values (not necessarily increasing). [...]
The core library containing the fundamental quantity classes and types consistent with the International System of Units (SI, in the French acronym).
Quantity types, units and constants commonly encountered in the field of thermodynamics and related sciences.
Quantity types and constants with universal application.