diff --git a/2018/ruby/day_03.rb b/2018/ruby/day_03.rb
new file mode 100644
index 0000000..af017ba
--- /dev/null
+++ b/2018/ruby/day_03.rb
@@ -0,0 +1,13 @@
+p ARGF.read.lines.each.with_object(Hash.new(0)) {|line, fabric|
+  line =~ /(\d+),(\d+): (\d+)x(\d+)$/
+  x = $1.to_i
+  y = $2.to_i
+  width = $3.to_i
+  height = $4.to_i
+
+  width.times {|dx|
+    height.times {|dy|
+      fabric[[y + dy, x + dx]] += 1
+    }
+  }
+}.count {|_,v| v > 1 }