diff --git a/semantica/normalize/number_normalizer.py b/semantica/normalize/number_normalizer.py
index 29911cb9..0846465d 100644
--- a/semantica/normalize/number_normalizer.py
+++ b/semantica/normalize/number_normalizer.py
@@ -370,8 +370,12 @@ class UnitConverter:
         Raises:
             ValidationError: If units are incompatible or not in same category
         """
-        from_unit = from_unit.lower()
-        to_unit = to_unit.lower()
+        # Normalize aliases before validating categories and looking up factors.
+        # The public API documents abbreviations such as ``kg`` and ``km``;
+        # validating those raw aliases against the canonical category lists
+        # incorrectly rejected otherwise supported conversions.
+        from_unit = self.normalize_unit(from_unit)
+        to_unit = self.normalize_unit(to_unit)
 
         # Validate units
         if not self.validate_units(from_unit, to_unit):
@@ -401,8 +405,8 @@ class UnitConverter:
         Returns:
             bool: True if units are compatible (same category), False otherwise
         """
-        from_unit = from_unit.lower()
-        to_unit = to_unit.lower()
+        from_unit = self.normalize_unit(from_unit)
+        to_unit = self.normalize_unit(to_unit)
 
         # Check if both units exist
         if (
@@ -498,6 +502,18 @@ class UnitConverter:
             "ml": "milliliter",
             "milliliter": "milliliter",
             "milliliters": "milliliter",
+            "ft": "foot",
+            "foot": "foot",
+            "feet": "foot",
+            "yd": "yard",
+            "yard": "yard",
+            "yards": "yard",
+            "mi": "mile",
+            "mile": "mile",
+            "miles": "mile",
+            "gal": "gallon",
+            "gallon": "gallon",
+            "gallons": "gallon",
         }
 
         return unit_map.get(unit_lower, unit_lower)
diff --git a/tests/normalize/test_number_normalizer.py b/tests/normalize/test_number_normalizer.py
index a7cf359c..2e06260c 100644
--- a/tests/normalize/test_number_normalizer.py
+++ b/tests/normalize/test_number_normalizer.py
@@ -1,4 +1,6 @@
 import unittest
+
+from semantica.utils.exceptions import ValidationError
 from semantica.normalize.number_normalizer import (
     NumberNormalizer,
     UnitConverter,
@@ -32,6 +34,19 @@ class TestUnitConverter(unittest.TestCase):
         # 1 kg = 1000 g
         self.assertEqual(self.converter.convert_units(1, "kg", "g"), 1000.0)
 
+    def test_convert_accepts_aliases_for_category_validation(self):
+        # Aliases are part of the documented API, not just parsing syntax.
+        self.assertEqual(self.converter.convert_units(1, "feet", "m"), 0.3048)
+        self.assertEqual(self.converter.convert_units(1, "gal", "liter"), 3.78541)
+
+    def test_convert_rejects_mismatched_categories_even_for_aliases(self):
+        # Both units normalize to canonical names first, so the category
+        # check sees real categories and rejects cross-category conversions.
+        with self.assertRaises(ValidationError):
+            self.converter.convert_units(1, "kg", "ft")
+        with self.assertRaises(ValidationError):
+            self.converter.convert_units(1, "gal", "lb")
+
     def test_normalize_unit(self):
         self.assertEqual(self.converter.normalize_unit("km"), "kilometer")
         self.assertEqual(self.converter.normalize_unit("kgs"), "kilogram")