Class::Measure - Create, compare, and convert units of measurement.


See Class::Measure::Length for some examples.


This is a base class that is inherited by the Class::Measure classes. This distribution comes with the class Class::Measure::Length.

The classes Class::Measure::Area, Class::Measure::Mass, Class::Measure::Space, Class::Measure::Temperature, and Class::Measure::Volume are planned and will be added soon.

The methods described here are available in all Class::Measure classes.



    my $m = new Class::Measure::Length( 1, 'inch' );

Creates a new measurement object. You must pass an initial measurement and default unit.

In most cases the measurement class that you are using will export a method to create new measurements. For example Class::Measure::Length exports the length() method.


  my $unit = $m->unit();

Returns the object's default unit.


    $m->set_unit( 'feet' );

Sets the default unit of the measurement.


    my $yards = $m->value('yards');
    my $val = $m->value();
    print "$m is the same as $val when in a string\n";

Retrieves the value of the measurement in the default unit. You may specify a unit in which case the value is converted to the unit and returned.

This method is also used to handle overloading of stringifying the object.


    my $m = length( 0, 'inches' );
    $m->set_value( 12 ); # 12 inches.
    $m->set_value( 1, 'foot' ); # 1 foot.

Sets the measurement in the default unit. You may specify a new default unit as well.


        'inch', 'foot', 'yard',

Registers one or more units for use in the specified class. Units should be in the singular, most common, form.


    my @units = Class::Measure::Length->units();

Returns a list of all registered units.


        ['feet','ft'] => 'foot',
        ['in','inches'] => 'inch',
        'yards' => 'yard'

Register alternate names for units. Expects two arguments per unit to alias. The first argument being the alias (scalar) or aliases (array ref), and the second argument being the unit to alias them to.


        12, 'inches' => 'foot',
        'yard' => '3', 'feet'

Registers a unit conversion. There are three distinct ways to specify a new conversion. Each requires three arguments.

    $count1, $unit1 => $unit2
    $unit1 => $count2, $unit2

These first two syntaxes create automatic reverse conversions as well. So, saying there are 12 inches in a foot implies that there are 1/12 feet in an inch.

    $unit1 => $unit2, $sub

The third syntax accepts a subroutine as the last argument the subroutine will be called with the value of $unit1 and it's return value will be assigned to $unit2. This third syntax does not create a reverse conversion automatically.


Please submit bugs and feature requests to the Class-Measure GitHub issue tracker:


    Aran Clary Deltac <>
    Roland van Ipenburg <>


This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.