diff --git a/Library/Homebrew/test/pathname_spec.rb b/Library/Homebrew/test/pathname_spec.rb
index da12d4347a..6e7dc34aaa 100644
--- a/Library/Homebrew/test/pathname_spec.rb
+++ b/Library/Homebrew/test/pathname_spec.rb
@@ -30,13 +30,13 @@ describe Pathname do
     describe "#abv" do
       context "when called on a directory" do
         it "returns a string with the file count and disk usage" do
-          expect(dir.abv).to eq("3 files, 1M")
+          expect(dir.abv).to eq("3 files, 1MB")
         end
       end
 
       context "when called on a file" do
         it "returns the disk usage" do
-          expect((dir/"a-file").abv).to eq("1M")
+          expect((dir/"a-file").abv).to eq("1MB")
         end
       end
     end
diff --git a/Library/Homebrew/test/utils_spec.rb b/Library/Homebrew/test/utils_spec.rb
index 040ad630be..b3fdedcb98 100644
--- a/Library/Homebrew/test/utils_spec.rb
+++ b/Library/Homebrew/test/utils_spec.rb
@@ -232,10 +232,10 @@ describe "globally-scoped helper methods" do
   specify "#disk_usage_readable" do
     expect(disk_usage_readable(1)).to eq("1B")
     expect(disk_usage_readable(1000)).to eq("1000B")
-    expect(disk_usage_readable(1024)).to eq("1K")
-    expect(disk_usage_readable(1025)).to eq("1K")
-    expect(disk_usage_readable(4_404_020)).to eq("4.2M")
-    expect(disk_usage_readable(4_509_715_660)).to eq("4.2G")
+    expect(disk_usage_readable(1024)).to eq("1KB")
+    expect(disk_usage_readable(1025)).to eq("1KB")
+    expect(disk_usage_readable(4_404_020)).to eq("4.2MB")
+    expect(disk_usage_readable(4_509_715_660)).to eq("4.2GB")
   end
 
   describe "#number_readable" do
diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index b129c73287..56ddfd611d 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -422,13 +422,13 @@ end
 def disk_usage_readable(size_in_bytes)
   if size_in_bytes >= 1_073_741_824
     size = size_in_bytes.to_f / 1_073_741_824
-    unit = "G"
+    unit = "GB"
   elsif size_in_bytes >= 1_048_576
     size = size_in_bytes.to_f / 1_048_576
-    unit = "M"
+    unit = "MB"
   elsif size_in_bytes >= 1_024
     size = size_in_bytes.to_f / 1_024
-    unit = "K"
+    unit = "KB"
   else
     size = size_in_bytes
     unit = "B"