diff --git a/binary_to_decimal.rb b/binary_to_decimal.rb
new file mode 100644
index 0000000..154249b
--- /dev/null
+++ b/binary_to_decimal.rb
@@ -0,0 +1,9 @@
+def binary_to_decimal(binary_array) #[01010100] 2**7 ~ 2**0
+  sum = 0
+  length = 8
+  binary_array.each do |i|
+    length -= 1
+    sum += i.to_i * (2**length)
+  end
+  sum
+end