diff a/src/hotspot/share/prims/unsafe.cpp b/src/hotspot/share/prims/unsafe.cpp
--- a/src/hotspot/share/prims/unsafe.cpp
+++ b/src/hotspot/share/prims/unsafe.cpp
@@ -777,10 +777,16 @@
   // but requires it to be linear in byte offset.
   return field_offset_from_byte_offset(scale) - field_offset_from_byte_offset(0);
 } UNSAFE_END
 
 
+UNSAFE_ENTRY(jlong, Unsafe_GetObjectSize0(JNIEnv* env, jobject o, jobject obj))
+  oop p = JNIHandles::resolve(obj);
+  return Universe::heap()->obj_size(p) * HeapWordSize;
+UNSAFE_END
+
+
 static inline void throw_new(JNIEnv *env, const char *ename) {
   jclass cls = env->FindClass(ename);
   if (env->ExceptionCheck()) {
     env->ExceptionClear();
     tty->print_cr("Unsafe: cannot throw %s because FindClass has failed", ename);
@@ -1238,10 +1244,11 @@
     {CC "staticFieldOffset0", CC "(" FLD ")J",           FN_PTR(Unsafe_StaticFieldOffset0)},
     {CC "staticFieldBase0",   CC "(" FLD ")" OBJ,        FN_PTR(Unsafe_StaticFieldBase0)},
     {CC "ensureClassInitialized0", CC "(" CLS ")V",      FN_PTR(Unsafe_EnsureClassInitialized0)},
     {CC "arrayBaseOffset0",   CC "(" CLS ")I",           FN_PTR(Unsafe_ArrayBaseOffset0)},
     {CC "arrayIndexScale0",   CC "(" CLS ")I",           FN_PTR(Unsafe_ArrayIndexScale0)},
+    {CC "getObjectSize0",     CC "(Ljava/lang/Object;)J", FN_PTR(Unsafe_GetObjectSize0)},
 
     {CC "defineClass0",       CC "(" DC_Args ")" CLS,    FN_PTR(Unsafe_DefineClass0)},
     {CC "allocateInstance",   CC "(" CLS ")" OBJ,        FN_PTR(Unsafe_AllocateInstance)},
     {CC "throwException",     CC "(" THR ")V",           FN_PTR(Unsafe_ThrowException)},
     {CC "compareAndSetReference",CC "(" OBJ "J" OBJ "" OBJ ")Z", FN_PTR(Unsafe_CompareAndSetReference)},
diff a/src/java.base/share/classes/java/util/Objects.java b/src/java.base/share/classes/java/util/Objects.java
--- a/src/java.base/share/classes/java/util/Objects.java
+++ b/src/java.base/share/classes/java/util/Objects.java
@@ -25,10 +25,11 @@
 
 package java.util;
 
 import jdk.internal.util.Preconditions;
 import jdk.internal.vm.annotation.ForceInline;
+import jdk.internal.misc.Unsafe;
 
 import java.util.function.Supplier;
 
 /**
  * This class consists of {@code static} utility methods for operating
@@ -423,6 +424,16 @@
     public static
     int checkFromIndexSize(int fromIndex, int size, int length) {
         return Preconditions.checkFromIndexSize(fromIndex, size, length, null);
     }
 
+    /**
+     * Return the size of the object in the heap.
+     *
+     * @param o an object
+     * @return the objects's size
+     * @since Valhalla
+     */
+    public static long getObjectSize(Object o) {
+        return Unsafe.getUnsafe().getObjectSize(o);
+    }
 }
diff a/src/java.base/share/classes/jdk/internal/misc/Unsafe.java b/src/java.base/share/classes/jdk/internal/misc/Unsafe.java
--- a/src/java.base/share/classes/jdk/internal/misc/Unsafe.java
+++ b/src/java.base/share/classes/jdk/internal/misc/Unsafe.java
@@ -1332,10 +1332,21 @@
         }
 
         return arrayIndexScale0(arrayClass);
     }
 
+    /**
+     * Return the size of the object in the heap.
+     * @param o an object
+     * @return the objects's size
+     * @since Valhalla
+     */
+    public long getObjectSize(Object o) {
+        if (o == null)
+            throw new NullPointerException();
+        return getObjectSize0(o);
+    }
 
     /** The value of {@code arrayIndexScale(boolean[].class)} */
     public static final int ARRAY_BOOLEAN_INDEX_SCALE
             = theUnsafe.arrayIndexScale(boolean[].class);
 
@@ -4186,10 +4197,11 @@
     private native Object staticFieldBase0(Field f);
     private native boolean shouldBeInitialized0(Class<?> c);
     private native void ensureClassInitialized0(Class<?> c);
     private native int arrayBaseOffset0(Class<?> arrayClass);
     private native int arrayIndexScale0(Class<?> arrayClass);
+    private native long getObjectSize0(Object o);
     private native Class<?> defineAnonymousClass0(Class<?> hostClass, byte[] data, Object[] cpPatches);
     private native int getLoadAverage0(double[] loadavg, int nelems);
 
 
     /**