Measured Rails Build Status Gem Version

This gem is the Rails integration for the measured gem.

It provides ActiveRecord adapter for persisting and retrieving measurements with their units, and model validations.


Using bundler, add to the Gemfile:

gem 'measured-rails'

Or stand alone:

$ gem install measured-rails



Columns are expected to have the _value and _unit suffix, and be DECIMAL and VARCHAR, and defaults are accepted. Customizing the column used to hold units is supported, see below for details.

class AddWeightAndLengthToThings < ActiveRecord::Migration
  def change
    add_column :things, :minimum_weight_value, :decimal, precision: 10, scale: 2
    add_column :things, :minimum_weight_unit, :string, limit: 12

    add_column :things, :total_length_value, :decimal, precision: 10, scale: 2, default: 0
    add_column :things, :total_length_unit, :string, limit: 12, default: "cm"

A column can be declared as a measurement with its measurement subclass:

class Thing < ActiveRecord::Base
  measured Measured::Weight, :minimum_weight
  measured Measured::Length, :total_length
  measured Measured::Volume, :total_volume

You can optionally customize the model's unit column by specifying it in the unit_field_name option, as follows:

class ThingWithCustomUnitAccessor < ActiveRecord::Base
  measured_length :length, :width, :height,     unit_field_name: :size_unit
  measured_weight :total_weight, :extra_weight, unit_field_name: :weight_unit
  measured_volume :total_volume, :extra_volume, unit_field_name: :volume_unit

Similarly, you can optionally customize the model's value column by specifying it in the value_field_name option, as follows:

class ThingWithCustomValueAccessor < ActiveRecord::Base
  measured_length :length, value_field_name: :custom_length
  measured_weight :total_weight, value_field_name: :custom_weight
  measured_volume :volume, value_field_name: :custom_volume

There are some simpler methods for predefined types:

class Thing < ActiveRecord::Base
  measured_weight :minimum_weight
  measured_length :total_length
  measured_volume :total_volume

This will allow you to access and assign a measurement object:

thing =
thing.minimum_weight =, "g")
thing.minimum_weight_unit     # "g"
thing.minimum_weight_value    # 10

Order of assignment does not matter, and each property can be assigned separately and with mass assignment:

params = { total_length_unit: "cm", total_length_value: "3" }
thing =
thing.total_length.to_s   # 3 cm


Validations are available:

class Thing < ActiveRecord::Base
  measured_length :total_length

  validates :total_length, measured: true

This will validate that the unit is defined on the measurement, and that there is a value.

Rather than true the validation can accept a hash with the following options:

  • message: Override the default "is invalid" message.
  • units: A subset of units available for this measurement. Units must be in existing measurement.
  • greater_than
  • greater_than_or_equal_to
  • equal_to
  • less_than
  • less_than_or_equal_to

All comparison validations require Measured::Measurable values, not scalars. Most of these options replace the numericality validator which compares the measurement/method name/proc to the column's value. Validations can also be combined with presence validator.

Note: Validations are strongly recommended since assigning an invalid unit will cause the measurement to return nil, even if there is a value:

thing =
thing.total_length_value = 1
thing.total_length_unit = "invalid"
thing.total_length  # nil


$ bundle exec rake test


  1. Fork it ( )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request