A sensible interface to Ruby's monotonic clock, inspired by Rust.

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Add this line to your application's Gemfile:

gem 'monotime'

And then execute:

$ bundle

Or install it yourself as:

$ gem install monotime

Monotime is tested on Ruby 2.7+, TruffleRuby, and JRuby.


require 'monotime'
# or, to automatically include Monotime::* in the global scope,
# as used by these examples:
require 'monotime/include'

Monotime offers a Duration type for describing spans of time, and an Instant type for describing points in time. Both operate at nanosecond resolution to the limits of whatever your Ruby implementation supports.

For example, to measure an elapsed time, either create an Instant to mark the start point, perform the action and then ask for the Duration that has elapsed since:

start =
elapsed = start.elapsed

Or use a convenience method:

elapsed = Duration.measure { do_something }
# or
return_value, elapsed = Duration.with_measure { compute_something }

Duration offers formatting:

Duration.millis(42).to_s       # => "42ms"
Duration.nanos(12345).to_s     # => "12.345μs"
Duration.secs(1.12345).to_s(2) # => "1.12s"


Duration.secs(10).millis    # => 10000.0
Duration.micros(12345).secs # => 0.012345

And basic mathematical operations:

(Duration.millis(42) + Duration.secs(1)).to_s  # => "1.042s"
(Duration.millis(42) - Duration.secs(1)).to_s  # => "-958ms"
(Duration.secs(42) * 2).to_s                   # => "84s"
(Duration.secs(42) / 2).to_s                   # => "21s"

Instant does some simple maths too:

# Instant - Duration => Instant
( - Duration.secs(1)).elapsed.to_s      # => "1.000014627s"

# Instant - Instant => Duration
( -                   # => "-5.585μs"

Duration and Instant are also Comparable with other instances of their type, and can be used in hashes, sets, and similar structures.


Duration can be used to sleep a thread, assuming it's positive (time travel is not yet implemented):

# Equivalent
sleep(Duration.secs(1).secs)  # => 1
Duration.secs(1).sleep        # => 1

So can Instant, taking a Duration and sleeping until the given Duration past the time the Instant was created, if any. This can be useful for maintaining a precise cadence between tasks:

interval = Duration.secs(60)
start =
loop do
  start += interval

Or you can declare an Instant in the future and sleep to that point:

interval = Duration.secs(60)
deadline = + interval
loop do
  deadline += interval

Instant#sleep returns a Duration which was slept, or a negative Duration indicating that the desired sleep point was in the past.

Duration duck typing

Operations taking a Duration can also accept any type which implements #to_nanos, returning an (Integer) number of nanoseconds the value represents.

For example, to treat built-in numeric types as second durations, you could do:

class Numeric
  def to_nanos
    Integer(self * 1_000_000_000)

(Duration.secs(1) + 41).to_s  # => "42s"
( - 42).to_s       # => "42.000010545s"


After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.

See Also

Core Ruby

For a zero-dependency alternative upon which monotime is based, see Process.clock_gettime.

Process::CLOCK_MONOTONIC is a safe default, but other options may offer better behaviour in face of NTP frequency skew or suspend/resume and should be evaluated carefully.

Other Gems

hitimes is a popular and mature alternative which also includes a variety of features for gathering statistics about measurements.

concurrent-ruby includes Concurrent.monotonic_time, which is at the time of writing a trivial proxy to the aforementioned Process::clock_gettime with Process::CLOCK_MONOTONIC.