diff --git a/src/main/scala/org/gerweck/scalafx/util/observable.scala b/src/main/scala/org/gerweck/scalafx/util/observable.scala
index 149bb5b..3b8d631 100644
--- a/src/main/scala/org/gerweck/scalafx/util/observable.scala
+++ b/src/main/scala/org/gerweck/scalafx/util/observable.scala
@@ -273,63 +273,3 @@ final class RichProperty[A, B](val inner: Property[A, B]) extends AnyVal {
 final class RichObjectProperty[A](val inner: ObjectProperty[A]) extends AnyVal {
   def readOnly: ReadOnlyObjectProperty[A] = inner
 }
-
-sealed trait ToObservableOps[-A, +B] {
-  def recalculate(a: A): B
-  def onChange(a: A)(b: => Unit): Unit
-}
-object ToObservableOps {
-  implicit def obOps[A] = new ToObservableOps[ObservableBuffer[A], Seq[A]] {
-    def recalculate(oba: ObservableBuffer[A]) = oba.toVector
-    def onChange(oba: ObservableBuffer[A])(b: => Unit) = oba onChange b
-  }
-  implicit def oaOps[A] = new ToObservableOps[ObservableArray[A, _, _], Seq[A]] {
-    def recalculate(oaa: ObservableArray[A, _, _]) = oaa.toVector
-    def onChange(oaa: ObservableArray[A, _, _])(b: => Unit) = oaa onChange b
-  }
-  implicit def osOps[A] = new ToObservableOps[ObservableSet[A], collection.immutable.Set[A]] {
-    def recalculate(os: ObservableSet[A]) = os.toSet
-    def onChange(os: ObservableSet[A])(b: => Unit) = os onChange b
-  }
-}
-
-object RichToObservable {
-  @inline final def toObservable[A, B](a: A)(implicit ops: ToObservableOps[A, B]): ReadOnlyObjectProperty[B] = {
-    @inline def recalculate(): B = ops.recalculate(a)
-    val originalValue = recalculate()
-    val prop = ObjectProperty[B](originalValue)
-    var prevValue = originalValue
-    ops.onChange(a) {
-      prop.synchronized {
-        val newVal = recalculate()
-        if (prevValue != newVal) {
-          prop.value = newVal
-          prevValue = newVal
-        }
-      }
-    }
-    prop
-  }
-}
-
-sealed trait RichObservableSeqLike[A] extends Any {
-  def observableSeqValue: ReadOnlyObjectProperty[Seq[A]]
-}
-
-final class RichObservableBuffer[A](val obs: ObservableBuffer[A]) extends AnyVal with RichObservableSeqLike[A] {
-  def observableSeqValue: ReadOnlyObjectProperty[Seq[A]] = {
-    RichToObservable.toObservable(obs)
-  }
-}
-
-final class RichObservableArray[A, B <: ObservableArray[A, B, C], C <: javafx.collections.ObservableArray[C]](val oaa: ObservableArray[A, B, C]) extends AnyVal with RichObservableSeqLike[A] {
-  def observableSeqValue: ReadOnlyObjectProperty[Seq[A]] = {
-    RichToObservable.toObservable(oaa)
-  }
-}
-
-final class RichObservableSet[A](val os: ObservableSet[A]) extends AnyVal {
-  def observableSetValue: ReadOnlyObjectProperty[Set[A]] = {
-    RichToObservable.toObservable(os)
-  }
-}
diff --git a/src/main/scala/org/gerweck/scalafx/util/observableCollection.scala b/src/main/scala/org/gerweck/scalafx/util/observableCollection.scala
new file mode 100644
index 0000000..3803baa
--- /dev/null
+++ b/src/main/scala/org/gerweck/scalafx/util/observableCollection.scala
@@ -0,0 +1,97 @@
+package org.gerweck.scalafx.util
+
+import language.implicitConversions
+
+import scalafx.beans.property._
+import scalafx.collections._
+
+sealed trait ToFlatObservable[-A, +B] extends Calculable[A, B]
+object ToFlatObservable extends CalculableObservable[ToFlatObservable[_, _]] {
+  implicit def obOps[A] = new ToFlatObservable[ObservableBuffer[A], Seq[A]] {
+    def recalculate(oba: ObservableBuffer[A]) = oba.toVector
+  }
+  implicit def oaOps[A] = new ToFlatObservable[ObservableArray[A, _, _], Seq[A]] {
+    def recalculate(oaa: ObservableArray[A, _, _]) = oaa.toVector
+  }
+  implicit def osOps[A] = new ToFlatObservable[ObservableSet[A], collection.immutable.Set[A]] {
+    def recalculate(os: ObservableSet[A]) = os.toSet
+  }
+}
+
+sealed trait ObservableSized[-A] extends Calculable[A, Int]
+object ObservableSized extends CalculableObservable[ObservableSized[_]] {
+  implicit def obSize[A] = new ObservableSized[ObservableBuffer[A]] {
+    def recalculate(oba: ObservableBuffer[A]) = oba.size
+  }
+  implicit def oaSize[A] = new ObservableSized[ObservableArray[A, _, _]] {
+    def recalculate(oaa: ObservableArray[A, _, _]) = oaa.size
+  }
+  implicit def osSize[A] = new ObservableSized[ObservableSet[A]] {
+    def recalculate(os: ObservableSet[A]) = os.size
+  }
+}
+
+sealed trait RichObservableSeqLike[A] extends Any {
+  def observableSeqValue: ReadOnlyObjectProperty[Seq[A]]
+  def observableSize: ReadOnlyObjectProperty[Int]
+}
+
+final class RichObservableBuffer[A](val obs: ObservableBuffer[A]) extends AnyVal with RichObservableSeqLike[A] {
+  def observableSeqValue: ReadOnlyObjectProperty[Seq[A]] = ToFlatObservable.toObservable(obs)
+  def observableSize = ObservableSized.toObservable(obs)
+}
+
+final class RichObservableArray[A, B <: ObservableArray[A, B, C], C <: javafx.collections.ObservableArray[C]](val oaa: ObservableArray[A, B, C]) extends AnyVal with RichObservableSeqLike[A] {
+  def observableSeqValue: ReadOnlyObjectProperty[Seq[A]] = ToFlatObservable.toObservable(oaa)
+  def observableSize = ObservableSized.toObservable(oaa)
+}
+
+final class RichObservableSet[A](val os: ObservableSet[A]) extends AnyVal {
+  def observableSetValue: ReadOnlyObjectProperty[Set[A]] = ToFlatObservable.toObservable(os)
+  def observableSize = ObservableSized.toObservable(os)
+}
+
+class CalculableObservable[O <: Calculable[_, _]] {
+  final def toObservable[A, B](a: A)(implicit ops: O with Calculable[A, B], cl: ChangeListenable[A]): ReadOnlyObjectProperty[B] = {
+    @inline def recalculate(): B = ops.recalculate(a)
+    val originalValue = recalculate()
+    val prop = ObjectProperty[B](originalValue)
+    var prevValue = originalValue
+    cl.onChange(a) {
+      prop.synchronized {
+        val newVal = recalculate()
+        if (prevValue != newVal) {
+          prop.value = newVal
+          prevValue = newVal
+        }
+      }
+    }
+    prop
+  }
+}
+
+/* Type Classes */
+
+trait Calculable[-A, +B] extends Any {
+  def recalculate(a: A): B
+}
+
+sealed trait ChangeListenable[-A] {
+  def onChange(a: A)(b: => Unit): Unit
+}
+object ChangeListenable {
+  implicit def obListenable[A]: ChangeListenable[ObservableBuffer[A]] = new ChangeListenable[ObservableBuffer[A]] {
+    def onChange(oba: ObservableBuffer[A])(b: => Unit) = oba onChange b
+  }
+  implicit def oaListenable[A]: ChangeListenable[ObservableArray[A, _, _]] = new ChangeListenable[ObservableArray[A, _, _]] {
+    def onChange(oaa: ObservableArray[A, _, _])(b: => Unit) = oaa onChange b
+  }
+  implicit def osListenable[A]: ChangeListenable[ObservableSet[A]] = new ChangeListenable[ObservableSet[A]] {
+    def onChange(osa: ObservableSet[A])(b: => Unit) = osa onChange b
+  }
+}
+
+sealed trait DeriveChanges[A] {
+  protected val evChange: ChangeListenable[A]
+  def onChange(a: A)(b: => Unit) = evChange.onChange(a)(b)
+}
diff --git a/version.sbt b/version.sbt
index 5877151..338b0ba 100644
--- a/version.sbt
+++ b/version.sbt
@@ -1 +1 @@
-version in ThisBuild := "0.8.4-SNAPSHOT"
+version in ThisBuild := "0.9.0-SNAPSHOT"