diff --git a/library/VectorBuilder/Builder.hs b/library/VectorBuilder/Builder.hs
--- a/library/VectorBuilder/Builder.hs
+++ b/library/VectorBuilder/Builder.hs
@@ -3,6 +3,7 @@
   Builder,
   empty,
   singleton,
+  size,
   vector,
   foldable,
 )
diff --git a/library/VectorBuilder/Core/Builder.hs b/library/VectorBuilder/Core/Builder.hs
--- a/library/VectorBuilder/Core/Builder.hs
+++ b/library/VectorBuilder/Core/Builder.hs
@@ -15,6 +15,13 @@
   Builder !Int !(A.Update element)
 
 
+-- |
+-- Gets the size of a Builder.
+{-# INLINE size #-}
+size :: Builder element -> Int
+size (Builder s _) = s
+
+
 -- * Initialisation
 
 -- |
diff --git a/vector-builder.cabal b/vector-builder.cabal
--- a/vector-builder.cabal
+++ b/vector-builder.cabal
@@ -1,7 +1,7 @@
 name:
   vector-builder
 version:
-  0.3.7.2
+  0.3.8
 synopsis:
   Vector builder
 description: