diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index cb41602970f..556ab23a0d1 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -386,6 +386,7 @@ Other Changes
 * SOLR-9915: PeerSync alreadyInSync check is not backwards compatible and results in full replication during a rolling restart
   (Tim Owen via noble)
 
+* SOLR-3990: Moves getIndexSize() from ReplicationHandler to SolrCore (Shawn Heisey)
 
 ==================  6.3.0 ==================
 
diff --git a/solr/core/src/java/org/apache/solr/core/SolrCore.java b/solr/core/src/java/org/apache/solr/core/SolrCore.java
index a9fec5ad142..08072e158f9 100644
--- a/solr/core/src/java/org/apache/solr/core/SolrCore.java
+++ b/solr/core/src/java/org/apache/solr/core/SolrCore.java
@@ -146,6 +146,7 @@ import org.apache.solr.update.processor.UpdateRequestProcessorChain;
 import org.apache.solr.update.processor.UpdateRequestProcessorChain.ProcessorInfo;
 import org.apache.solr.update.processor.UpdateRequestProcessorFactory;
 import org.apache.solr.util.DefaultSolrThreadFactory;
+import org.apache.solr.util.NumberUtils;
 import org.apache.solr.util.PropertiesInputStream;
 import org.apache.solr.util.RefCounted;
 import org.apache.solr.util.plugin.NamedListInitializedPlugin;
@@ -391,6 +392,22 @@ public final class SolrCore implements SolrInfoMBean, Closeable {
   public IndexReaderFactory getIndexReaderFactory() {
     return indexReaderFactory;
   }
+  
+  public long getIndexSize() {
+    Directory dir;
+    long size = 0;
+    try {
+      dir = directoryFactory.get(getIndexDir(), DirContext.DEFAULT, solrConfig.indexConfig.lockType);
+      try {
+        size = DirectoryFactory.sizeOfDirectory(dir);
+      } finally {
+        directoryFactory.release(dir);
+      }
+    } catch (IOException e) {
+      SolrException.log(log, "IO error while trying to get the size of the Directory", e);
+    }
+    return size;
+  }
 
   @Override
   public String getName() {
@@ -2653,6 +2670,9 @@ public final class SolrCore implements SolrInfoMBean, Closeable {
     lst.add("refCount", getOpenCount());
     lst.add("instanceDir", resourceLoader.getInstancePath());
     lst.add("indexDir", getIndexDir());
+    long size = getIndexSize();
+    lst.add("sizeInBytes", size);
+    lst.add("size", NumberUtils.readableSize(size));
 
     CoreDescriptor cd = getCoreDescriptor();
     if (cd != null) {
diff --git a/solr/core/src/java/org/apache/solr/handler/ReplicationHandler.java b/solr/core/src/java/org/apache/solr/handler/ReplicationHandler.java
index 08b6f39aa05..edf5e949d24 100644
--- a/solr/core/src/java/org/apache/solr/handler/ReplicationHandler.java
+++ b/solr/core/src/java/org/apache/solr/handler/ReplicationHandler.java
@@ -813,22 +813,6 @@ public class ReplicationHandler extends RequestHandlerBase implements SolrCoreAw
     numTimesReplicated++;
   }
 
-  long getIndexSize() {
-    Directory dir;
-    long size = 0;
-    try {
-      dir = core.getDirectoryFactory().get(core.getIndexDir(), DirContext.DEFAULT, core.getSolrConfig().indexConfig.lockType);
-      try {
-        size = core.getDirectoryFactory().size(dir);
-      } finally {
-        core.getDirectoryFactory().release(dir);
-      }
-    } catch (IOException e) {
-      SolrException.log(LOG, "IO error while trying to get the size of the Directory", e);
-    }
-    return size;
-  }
-
   @Override
   public String getDescription() {
     return "ReplicationHandler provides replication of index and configuration files from Master to Slaves";
@@ -855,7 +839,7 @@ public class ReplicationHandler extends RequestHandlerBase implements SolrCoreAw
   public NamedList getStatistics() {
     NamedList list = super.getStatistics();
     if (core != null) {
-      list.add("indexSize", NumberUtils.readableSize(getIndexSize()));
+      list.add("indexSize", NumberUtils.readableSize(core.getIndexSize()));
       CommitVersionInfo vInfo = (core != null && !core.isClosed()) ? getIndexVersion(): null;
       list.add("indexVersion", null == vInfo ? 0 : vInfo.version);
       list.add(GENERATION, null == vInfo ? 0 : vInfo.generation);
@@ -907,7 +891,7 @@ public class ReplicationHandler extends RequestHandlerBase implements SolrCoreAw
     NamedList<Object> master = new SimpleOrderedMap<>();
     NamedList<Object> slave = new SimpleOrderedMap<>();
 
-    details.add("indexSize", NumberUtils.readableSize(getIndexSize()));
+    details.add("indexSize", NumberUtils.readableSize(core.getIndexSize()));
     details.add("indexPath", core.getIndexDir());
     details.add(CMD_SHOW_COMMITS, getCommits());
     details.add("isMaster", String.valueOf(isMaster));