Read this in X minutes Liquid Filter Plugin (for Jekyll)

reading_time.rb

# Outputs the reading time

# Read this in “about 4 minutes”
# Put into your _plugins dir in your Jekyll site
# Usage: Read this in about {{ page.content | reading_time }}

module ReadingTimeFilter
	def reading_time( input )
		words_per_minute = 180

		words = input.split.size;
		minutes = ( words / words_per_minute ).floor
		minutes_label = minutes === 1 ? " minute" : " minutes"
		minutes > 0 ? "about #{minutes} #{minutes_label}" : "less than 1 minute"
	end
end

Liquid::Template.register_filter(ReadingTimeFilter)