diff --git a/src/MDUnitsSet.php b/src/MDUnitsSet.php
index a8e861a..d7067c2 100644
--- a/src/MDUnitsSet.php
+++ b/src/MDUnitsSet.php
@@ -11,7 +11,7 @@ declare(strict_types = 1);
  */
 final class MDUnitsSet extends MDValueSet {
 
-    const UNITS_LENGTH = ['', 'm', 'dm', 'cm', 'mm'];
+    const UNITS_LENGTH = ['', 'm', 'dm', 'cm', 'mm', 'ft', 'in'];
     const UNITS_WEIGHT = ['', 't', 'kg', 'g'];
 
     const UNITS_LENGTH_TO_MILLIMETER = [