Quantify

A type-safe units of measurement library for Dart, providing an elegant syntax for unit conversions with good precision and optimal performance.

Why quantify?

quantify makes working with physical units in Dart safer, more readable, and efficient:

• Type Safety: Prevents unit mismatch errors at compile-time.
• Elegant API: Intuitive syntax like 10.m or length.inKm.
• Precise & Performant: Uses double and direct conversion factors for speed and to minimize rounding errors.
• Immutable: Quantity objects are immutable for safer code.
• Configurable Output: Highly flexible toString() for customized formatting.
• Lightweight: Minimal dependencies.

Quick Start

import 'package:quantify/quantify.dart';
// For locale-specific number formatting, add 'intl' to your pubspec.yaml
// and import 'package:intl/intl.dart';

void main() {
  // Create quantities
  final pathA = 1500.m;
  final pathB = 2.5.km;

  // Convert to value / a new Quantity object
  double pathInKm = pathA.inKm;
  final pathAsKm = pathA.asKm;

  // Convert and print
  print(pathA.toString(targetUnit: LengthUnit.kilometer, fractionDigits: 1));  // Output: "1.5 km"
  print(pathB.toString(targetUnit: LengthUnit.mile, fractionDigits: 2));  // Output: "1.55 mi" (approx.)

  // Arithmetic
  final distance = pathA + pathB; // pathB is converted to meters
  print(distance.toString(fractionDigits: 0));  // Output: "4000 m"
  print(distance.toString(
    targetUnit: LengthUnit.yard,
    fractionDigits: 0,
  ));  // Output: "4374 yd" (approx., with non-breaking space)

  // Locale-specific example (if 'intl' is used)
  // final distanceDE = 1234.567.m;
  print(distanceDE.toString(
    targetUnit: LengthUnit.kilometer,
    fractionDigits: 2,
    locale: 'de_DE',
  ));  // Output: "1,23 km"
}

Installation

Add to your pubspec.yaml:

dependencies:
  quantify: ^0.4.0 # Or latest version
  # Optional, for locale-specific number formatting:
  # intl: ^0.19.0

Then run dart pub get or flutter pub get.

Supported Units

The library supports a comprehensive range of physical quantities, including all 7 SI base units and many derived units:

Quantity Type	Status	Units Available	Notes / SI Base Unit Ref.
Length	✅	m (meter), km, hm, dam, dm, cm, mm, μm, nm, pm, fm, in, ft, yd, mi, nmi, AU, ly, pc, Å	SI Base: Meter (m)
Mass	✅	kg (kilogram), hg, dag, g, dg, cg, mg, μg, ng, t, lb, oz, st, slug, short ton, long ton, u, ct	SI Base: Kilogram (kg)
Time	✅	s (second), μs, ns, ps, ms, min, h, d, wk, mo, yr	SI Base: Second (s)
Electric Current	✅	A (ampere), mA, μA, nA, kA	SI Base: Ampere (A)
Temperature	✅	K (kelvin), °C (celsius), °F (fahrenheit), °R (rankine)	SI Base: Kelvin (K)
Amount of Substance	✅	mol (mole), mmol, μmol, nmol, pmol, kmol	SI Base: Mole (mol)
Luminous Intensity	✅	cd (candela), mcd, kcd	SI Base: Candela (cd)
--- Derived ---
Pressure	✅	Pa (Pascal), atm, bar, psi, Torr, mmHg, inHg, kPa, hPa, mbar, cmH₂O, inH₂O	Derived SI: N/m²
Angle	✅	rad (radian), ° (degree), grad, rev, arcmin ('), arcsec ("), mrad	Derived SI: dimensionless
Angular Velocity	✅	rad/s, °/s, rpm, rps	Derived SI: 1/s
Area	🗓️	m² (square meter), km², cm², ha (hectare), acre ...	Derived SI
Volume	🗓️	m³ (cubic meter), L (liter), mL, cm³, gal (gallon), fl oz ...	Derived SI
Speed / Velocity	🗓️	m/s (meter per second), km/h, mph, knot ...	Derived SI
Acceleration	🗓️	m/s² (meter per second squared), g (standard gravity) ...	Derived SI
Force	🗓️	N (Newton), lbf (pound-force), dyn (dyne) ...	Derived SI: kg·m/s²
Energy / Work	🗓️	J (Joule), kWh (kilowatt-hour), cal (calorie), eV (electronvolt) ...	Derived SI: N·m
Power	💡	W (Watt), hp (horsepower) ...	Derived SI: J/s
Frequency	💡	Hz (Hertz), kHz, MHz ...	Derived SI: 1/s

Detailed Usage

Creating Quantities

Use extension methods on num for readability:

final myLength = 25.5.m;
final anotherLength = 10.ft; // feet
final verySmall = 500.nm; // nanometers
final astronomical = 4.2.ly; // light years

Or use the constructor of the specific Quantity class:

final specificLength = Length(5.0, LengthUnit.yard);

Converting and Retrieving Values

1. Get Numerical Value: Use in[UnitName] getters or getValue(TargetUnit).

   final oneMile = 1.0.mi;
   double milesInKm = oneMile.inKm; // approx 1.609344
   double milesInMeters = oneMile.getValue(LengthUnit.meter); // approx 1609.344
   
   final smallDistance = 1.um; // micrometer
   double inNanometers = smallDistance.inNm; // 1000.0
   

2. Get New Quantity Object: Use convertTo(TargetUnit) or as[UnitName] getters.

   final tenMeters = 10.m;
   final tenMetersInFeetObj = tenMeters.convertTo(LengthUnit.foot);
   // tenMetersInFeetObj is Length(approx 32.8084, LengthUnit.foot)
   final tenMetersInKmObj = tenMeters.asKm;
   // tenMetersInKmObj is Length(0.01, LengthUnit.kilometer)
   

Formatting Output with toString()

The toString() method on Quantity objects is highly configurable:

final myDistance = 1578.345.m;

// Default
print(myDistance.toString()); // "1578.345 m"

// Convert to kilometers, 2 fraction digits
print(myDistance.toString(targetUnit: LengthUnit.kilometer, fractionDigits: 2));
// Output: "1.58 km"

// Scientific notation with micrometers
final smallLength = 0.000523.m;
print(smallLength.toString(targetUnit: LengthUnit.micrometer, fractionDigits: 0));
// Output: "523 μm"

Arithmetic Operations

Standard arithmetic operators (+, -, *, / by a scalar) are overloaded. The result's unit is typically that of the left-hand operand. Temperature has specific arithmetic rules.

final segment1 = 500.m;
final segment2 = 0.25.km; // 250 meters
final total = segment1 + segment2; // Result is in meters
print(total.toString()); // "750.0 m"

final scaled = segment1 * 3;
print(scaled.toString()); // "1500.0 m"

// Work with different scales
final bigMass = 5.t; // tonnes
final smallMass = 250.g; // grams
final combined = bigMass + smallMass; // Result: 5.00025 t

Comparisons & Sorting

Quantities are Comparable, allowing them to be sorted even if their units differ. compareTo() is used for magnitude comparison. The == operator checks for equal value AND unit.

final oneMeter = 1.m;
final hundredCm = 100.cm;
final oneYard = 1.yd;

print(oneMeter.compareTo(hundredCm) == 0); // true (magnitudes are equal)
print(oneMeter == hundredCm);          // false (units are different)

// Sort mixed units
final lengths = [1.mi, 2000.m, 1.km, 5000.ft];
lengths.sort(); // Sorts by physical magnitude

Goals & Roadmap

• V1.0 (Current): All 7 SI base units with comprehensive unit coverage
• V2.0 and Beyond:
  • High Precision: Support for Decimal.
  • Enhanced Quantity Arithmetic: e.g., Distance / Time = Speed.
  • More Derived Units: Area, Volume, Speed, Force, Energy, Power, etc.
  • Serialization support.

Contributing

Contributions are welcome! Please open an Issue or a Pull Request.

License

MIT License - see the LICENSE file.