diff --git a/bits-extra.cabal b/bits-extra.cabal
--- a/bits-extra.cabal
+++ b/bits-extra.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 547b5605d3febfb841362a7a119ad0091b5184712d7fdb7698dc5ae94e7f4249
+-- hash: 6cc41f475c233d2d1c9c4bd300ca0f7f274a3964bd2de19b0f2e19e670724c22
 
 name:           bits-extra
-version:        0.0.0.2
+version:        0.0.0.3
 description:    Please see the README on Github at <https://github.com/haskell-works/bits-extra#readme>
 homepage:       https://github.com/haskell-works/bits-extra#readme
 bug-reports:    https://github.com/haskell-works/bits-extra/issues
@@ -37,6 +37,7 @@
   build-depends:
       base >=4.7 && <5
     , ghc-prim
+    , vector
   if (flag(bmi2)) && (impl(ghc >=8.4.1))
     ghc-options: -mbmi2 -msse4.2
     cpp-options: -DBMI2_ENABLED
@@ -46,6 +47,7 @@
       Data.Bits.Pext
       Data.Bits.Pext.Slow
   other-modules:
+      Data.Bits.BitSize
       Data.Bits.Pdep.Prim
       Data.Bits.Pext.Prim
       Paths_bits_extra
diff --git a/src/Data/Bits/BitSize.hs b/src/Data/Bits/BitSize.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Bits/BitSize.hs
@@ -0,0 +1,79 @@
+module Data.Bits.BitSize where
+
+import Data.Functor.Identity
+import Data.Int
+import Data.Word
+
+import qualified Data.Bits            as B
+import qualified Data.Vector          as DV
+import qualified Data.Vector.Storable as DVS
+
+class BitSize a where
+  bitSize :: a -> Int
+  bitCount :: a -> Word64
+  bitCount = fromIntegral . bitSize
+  {-# INLINE bitCount #-}
+
+instance BitSize () where
+  bitSize _ = 0
+  {-# INLINE bitSize #-}
+
+instance BitSize Bool where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Word where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Word64 where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Word32 where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Word16 where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Word8 where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Int where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Int64 where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Int32 where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Int16 where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize Int8 where
+  bitSize = B.finiteBitSize
+  {-# INLINE bitSize #-}
+
+instance BitSize a => BitSize (Identity a) where
+  bitSize = foldl (\a b -> a + bitSize b) 0
+  {-# INLINE bitSize #-}
+
+instance BitSize a => BitSize [a] where
+  bitSize = foldl (\a b -> a + bitSize b) 0
+  {-# INLINE bitSize #-}
+
+instance BitSize a => BitSize (DV.Vector a) where
+  bitSize = DV.foldl (\a b -> a + bitSize b) 0
+  {-# INLINE bitSize #-}
+
+instance (BitSize a, DVS.Storable a) => BitSize (DVS.Vector a) where
+  bitSize = DVS.foldl (\a b -> a + bitSize b) 0
+  {-# INLINE bitSize #-}