diff --git a/lib/unit_conversion/conversions.rb b/lib/unit_conversion/conversions.rb
index f5cccb2..3349fdf 100644
--- a/lib/unit_conversion/conversions.rb
+++ b/lib/unit_conversion/conversions.rb
@@ -98,9 +98,9 @@ module UnitConversion
     def convert(value_unit)
       if value_unit.unit && value_unit.unit.metric?
         if value_unit.mass?
-          value_unit = value_unit.convert('oz').auto_unit
+          value_unit = value_unit.convert('oz').auto_unit.change_formatter(RationalFormatter.new)
         elsif value_unit.volume?
-          value_unit = value_unit.convert('cup').auto_unit
+          value_unit = value_unit.convert('cup').auto_unit.change_formatter(RationalFormatter.new)
         end
       end
 
diff --git a/lib/unit_conversion/value_unit.rb b/lib/unit_conversion/value_unit.rb
index 4623ca0..db1f6b1 100644
--- a/lib/unit_conversion/value_unit.rb
+++ b/lib/unit_conversion/value_unit.rb
@@ -74,6 +74,11 @@ module UnitConversion
       unit.unitwise(value.value)
     end
 
+    def change_formatter(formatter)
+      @formatter = formatter
+      self
+    end
+
     # Returns a new ValueUnit scaled by the given factor
     def scale(factor)
       if factor.present?
diff --git a/spec/lib/unit_conversion/conversions_spec.rb b/spec/lib/unit_conversion/conversions_spec.rb
index 9420b15..8a69423 100644
--- a/spec/lib/unit_conversion/conversions_spec.rb
+++ b/spec/lib/unit_conversion/conversions_spec.rb
@@ -36,6 +36,16 @@ RSpec.describe UnitConversion::Conversion do
     end
   end
 
+  describe UnitConversion::StandardUnitConversion do
+    it 'converts standard units' do
+      expect(UnitConversion::StandardUnitConversion.new.convert(get_value_unit(200, 'ml')).unit.to_s).to eq 'cup'
+      expect(UnitConversion::StandardUnitConversion.new.convert(get_value_unit(200, 'ml')).pretty_value).to eq '7/8'
+
+      expect(UnitConversion::StandardUnitConversion.new.convert(get_value_unit(5, 'liter')).unit.to_s).to eq 'gallon'
+      expect(UnitConversion::StandardUnitConversion.new.convert(get_value_unit(5, 'liter')).pretty_value).to eq '1 5/16'
+    end
+  end
+
   describe UnitConversion::ConvertConversion do
     it 'converts standard units' do
       expect(UnitConversion::ConvertConversion.new(get_unit('tbsp')).convert(get_value_unit(1, 'cups')).raw_value).to eq 16