bm.rb

# gem install benchmark-ips
require 'benchmark/ips'

require 'ruby-measurement'
require 'ruby-units'

Measurement.define(:tempC) do |unit|
  unit.convert_to(:tempK) { |value| value + 273.15 }
end

Measurement.define(:tempK) do |unit|
end

Measurement.define(:millibar) do |unit|
  unit.convert_to(:Pa) { |value| value * 100 }
end

Measurement.define(:Pa) do |unit|
end

kmh_to_ms_factor = Rational(1000, 3600)

Measurement.define('km/h') do |unit|
  unit.convert_to('m/s') { |value| value * kmh_to_ms_factor }
end

Measurement.define('m/s') do |unit|
end

Benchmark.ips do |x|
  x.report("ruby-measurement") do
    Measurement.new(323.5, 'tempC').convert_to('tempK').quantity
    Measurement.new(323.5, 'millibar').convert_to('Pa').quantity
    Measurement.new(323.5, 'km/h').convert_to('m/s').quantity
    Measurement.new(323.5, 'tempC').convert_to('tempK')
    Measurement.new(323.5, 'km/h').convert_to('m/s')
  end
  x.report("ruby-units") do
    Unit.new(323.5, 'tempC').convert_to('tempK').scalar
    Unit.new(323.5, 'millibar').convert_to('Pa').scalar
    Unit.new(323.5, 'km/h').convert_to('m/s').scalar
    Unit.new(323.5, 'tempC').convert_to('tempK')
    Unit.new(323.5, 'km/h').convert_to('m/s')
  end

  x.compare!
end

output.txt

$ ruby bm.rb
Warming up --------------------------------------
    ruby-measurement     5.713k i/100ms
          ruby-units     6.000  i/100ms
Calculating -------------------------------------
    ruby-measurement     63.247k (± 2.4%) i/s -    319.928k in   5.061386s
          ruby-units     64.435  (± 3.1%) i/s -    324.000  in   5.031803s

Comparison:
    ruby-measurement:    63247.3 i/s
          ruby-units:       64.4 i/s - 981.57x  slower