Libraries for converting physical units (kilograms, pounds) in Ruby?

Question

I know Rails has some nice helpers for date and time management. Is there an already-working project consisting of, or incorporating a clean DSL for standard units and their conversions? Any project with helpers for the conversion between the two systems' basic units of length and weight would work. Thank you!

Answer 1

Wow, there are quite a few more of these than I expected. Here is what I believe to be a complete list, in alphabetical order, with example usage stripped from their documentation. I also noted if I couldn't get them running locally.

1. Alchemist

   require 'alchemist'
   Alchemist.setup
   8.miles.to.meters
   10.kilometers + 1.mile # 11.609344 kilometers
   

2. measurement

   This one appears out of date, the last commit was 5 years ago, and it doesn't seem to run on 1.9.3 for me.

   include Measurement::Length
   Inch.new(12).to_centimeters # => #<Measurement::Length::Centimeter:0x173c2b4 @units=30.48>
   

3. Phys-Units

   require "phys/units"
   Q = Phys::Quantity
   U = Phys::Unit
   
   Q[1.23,'km'] + Q[4.56,'m']    #=> Phys::Quantity[1.23456,'km']
   Q[123,'mile'] / Q[2,'hr']     #=> Phys::Quantity[61,'mile/hr']
   Q[61,'miles/hr'].want('m/s')  #=> Phys::Quantity[27.26944,'m/s']
   Q[1.0,'are'] == Q[10,'m']**2  #=> true
   

4. Quantity

   Note that this one states that it is not production ready in the README.

   require 'quantity/all'
   1.meter                                         #=> 1 meter
   1.meter.to_feet                                 #=> 3.28083... foot
   c = 299792458.meters / 1.second                 #=> 299792458 meter/second
   
   newton = 1.meter * 1.kilogram / 1.second**2     #=> 1 meter*kilogram/second^2
   newton.to_feet                                  #=> 3.28083989501312 foot*kilogram/second^2
   newton.convert(:feet)                                   #=> 3.28083989501312 foot*kilogram/second^2
   jerk_newton = newton / 1.second                         #=> 1 meter*kilogram/second^3
   jerk_newton * 1.second == newton                        #=> true
   

5. SY

   See Boris Stitnickey's answer.

6. ruby-measurement

   require 'ruby-measurement'
   
   measurement = Measurement.parse('3 feet')  # => 3.0 ft.
   measurement.convert_to(:yards)             # => 1.0 yd.
   measurement.convert_to(:in)                # => 36.0 in.
   measurement.convert_to(:inches)            # => 36.0 in.
   
   measurement1 = Measurement.parse('3 feet') # => 3.0 ft.
   measurement2 = Measurement.parse('6 inch') # => 6.0 in.
   measurement1 + measurement2                # => 3.5 ft.
   

7. ruby-units

   require 'ruby-units'
   
   unit = Unit("mm")                # unit only (defaults to a scalar of 1)
   unit = Unit("1 mm")              # create a simple unit
   unit = Unit("1 kg*m^2/s^2")      # complex unit
   
   unit1 =~ unit2                   # true if units are compatible
   unit1.compatible?(unit2)         # true if units are compatible
   
   unit1 = unit >> "ft"             # convert to 'feet'
   unit3 = unit1 + unit2            # resulting object will have the units of unit1
   
   unit1 === unit2                  # true if units and quantity are the same, even if 'equivalent' by <=>
   unit.convert_to('ft')            # convert
   (unit1 + unit2).convert_to('ft') # converts result to 'ft'
   

8. Units for Ruby

   require 'units'
   
   three_meters = 3.meters
   two_meters = 2.m
   one_inch = 1.inch
   
   3.meters.to_inches # => 118.1103 inch
   10.inches.to_mm    # => 254.0 millimeter
   

9. Unitwise

   require 'unitwise/ext'
   
   1.yard == (1.foot * 3)                       # => true
   
   1.quart < 1.liter                            # => true
   
   2.meter + 3.inch - 1.yard                    # => <Unitwise::Measurement 1.1618 meter>
   
   1.convert_to('kg.m2/s2') == 1.joule          # => true
   
   (20.kg * 9.8.convert_to('m/s2')).to_pound_force # => <Unitwise::Measurement 44.06255284754326 pound_force>
   
   (300.horsepower * 60.second).to_calorie      # => <Unitwise::Measurement 3208077.8414151203 calorie>
   

10. Van/Unit

    Like another poster, I had trouble getting this working. However, you can see Jörg W Mittag's answer for usage.

As the author of Unitwise, it might be obvious that it's my favorite out of the group. I encourage you to at least check it out, though.

Answer 2

Try awesome Alchemist.

......

Answer 3

Take a look at Tom Sawyer's Van/Unit

This is from the homepage:

require 'van/units'
include Units

1.mile.to(feet)
1.acre.to(yd**2)
1.acre.to(sq_yd)
1.gallon.to(self.L)
1.lb.to(kg)
1.m.s.to(m.s)
1.sq_mi.to(km**2)
1.mile.to(km)
1.usd.to(twd)
1.bit/s + 8.bytes/s