diff --git a/src/main/java/org/codelibs/fess/ds/callback/IndexUpdateCallbackImpl.java b/src/main/java/org/codelibs/fess/ds/callback/IndexUpdateCallbackImpl.java
index 85f3e2105..3c2241b3c 100644
--- a/src/main/java/org/codelibs/fess/ds/callback/IndexUpdateCallbackImpl.java
+++ b/src/main/java/org/codelibs/fess/ds/callback/IndexUpdateCallbackImpl.java
@@ -112,7 +112,7 @@ public class IndexUpdateCallbackImpl implements IndexUpdateCallback {
 
             final Long contentLength = DocumentUtil.getValue(dataMap, fessConfig.getIndexFieldContentLength(), Long.class);
             if (contentLength != null) {
-                docList.addContentSize(contentLength.longValue());
+                docList.addContentSize(indexingHelper.calculateDocumentSize(dataMap, contentLength.longValue()));
                 if (docList.getContentSize() >= maxDocumentRequestSize) {
                     indexingHelper.sendDocuments(fessEsClient, docList);
                 }
diff --git a/src/main/java/org/codelibs/fess/helper/IndexingHelper.java b/src/main/java/org/codelibs/fess/helper/IndexingHelper.java
index b554d640c..3b8943358 100644
--- a/src/main/java/org/codelibs/fess/helper/IndexingHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/IndexingHelper.java
@@ -203,6 +203,14 @@ public class IndexingHelper {
 
     }
 
+    public long calculateDocumentSize(final Map<String, Object> dataMap, final long size) {
+        final long objSize = MemoryUtil.sizeOf(dataMap);
+        if (objSize > size) {
+            return objSize;
+        }
+        return size;
+    }
+
     public void setMaxRetryCount(final int maxRetryCount) {
         this.maxRetryCount = maxRetryCount;
     }
@@ -214,4 +222,5 @@ public class IndexingHelper {
     public void setRequestInterval(final long requestInterval) {
         this.requestInterval = requestInterval;
     }
+
 }
diff --git a/src/main/java/org/codelibs/fess/util/MemoryUtil.java b/src/main/java/org/codelibs/fess/util/MemoryUtil.java
index 6562169fe..a7e7aaaf1 100644
--- a/src/main/java/org/codelibs/fess/util/MemoryUtil.java
+++ b/src/main/java/org/codelibs/fess/util/MemoryUtil.java
@@ -15,6 +15,12 @@
  */
 package org.codelibs.fess.util;
 
+import java.time.LocalDateTime;
+import java.time.ZonedDateTime;
+import java.util.Collection;
+import java.util.Date;
+import java.util.Map;
+
 import org.apache.commons.io.FileUtils;
 import org.codelibs.core.lang.StringUtil;
 
@@ -42,4 +48,40 @@ public final class MemoryUtil {
         final long totalBytes = runtime.totalMemory();
         return totalBytes - freeBytes;
     }
+
+    public static long sizeOf(final Object obj) {
+        if (obj == null) {
+            return 0L;
+        } else if (obj instanceof String) {
+            return ((String) obj).length() + 56L;
+        } else if (obj instanceof Number) {
+            return 24L;
+        } else if (obj instanceof Date) {
+            return 32L;
+        } else if (obj instanceof LocalDateTime) {
+            return 80L;
+        } else if (obj instanceof ZonedDateTime) {
+            return 2128L;
+        } else if (obj instanceof Object[]) {
+            long size = 0;
+            for (final Object value : (Object[]) obj) {
+                size += sizeOf(value);
+            }
+            return size;
+        } else if (obj instanceof Collection<?>) {
+            long size = 0;
+            for (final Object value : (Collection<?>) obj) {
+                size += sizeOf(value);
+            }
+            return size;
+        } else if (obj instanceof Map<?, ?>) {
+            long size = 0;
+            for (final Map.Entry<?, ?> entry : ((Map<?, ?>) obj).entrySet()) {
+                size += sizeOf(entry.getKey());
+                size += sizeOf(entry.getValue());
+            }
+            return size;
+        }
+        return 16L;
+    }
 }
diff --git a/src/test/java/org/codelibs/fess/util/MemoryUtilTest.java b/src/test/java/org/codelibs/fess/util/MemoryUtilTest.java
index a5a09eb4e..404d9efb5 100644
--- a/src/test/java/org/codelibs/fess/util/MemoryUtilTest.java
+++ b/src/test/java/org/codelibs/fess/util/MemoryUtilTest.java
@@ -15,7 +15,15 @@
  */
 package org.codelibs.fess.util;
 
+import java.time.LocalDateTime;
+import java.time.ZonedDateTime;
+import java.util.Date;
+
+import org.codelibs.core.collection.Maps;
 import org.codelibs.fess.unit.UnitFessTestCase;
+import org.codelibs.sai.internal.ir.debug.ObjectSizeCalculator;
+
+import com.google.common.collect.Lists;
 
 public class MemoryUtilTest extends UnitFessTestCase {
 
@@ -23,4 +31,28 @@ public class MemoryUtilTest extends UnitFessTestCase {
         assertTrue(MemoryUtil.getUsedMemory() >= 0);
     }
 
+    public void test_sizeOf() throws Exception {
+        // System.out.println("size: " + getObjectSize(""));
+        assertEquals(24L, MemoryUtil.sizeOf(Integer.MAX_VALUE));
+        assertEquals(24L, MemoryUtil.sizeOf(Long.MAX_VALUE));
+        assertEquals(24L, MemoryUtil.sizeOf(Short.MAX_VALUE));
+        assertEquals(24L, MemoryUtil.sizeOf(Float.MAX_VALUE));
+        assertEquals(24L, MemoryUtil.sizeOf(Double.MAX_VALUE));
+        assertEquals(24L, MemoryUtil.sizeOf(Byte.MAX_VALUE));
+        assertEquals(16L, MemoryUtil.sizeOf(Boolean.TRUE));
+        assertEquals(32L, MemoryUtil.sizeOf(new Date()));
+        assertEquals(80L, MemoryUtil.sizeOf(LocalDateTime.now()));
+        assertEquals(2128L, MemoryUtil.sizeOf(ZonedDateTime.now()));
+        assertEquals(66L, MemoryUtil.sizeOf("1234567890"));
+        assertEquals(76L, MemoryUtil.sizeOf("12345678901234567890"));
+        assertEquals(66L, MemoryUtil.sizeOf(new String[] { "1234567890" }));
+        assertEquals(132L, MemoryUtil.sizeOf(new String[] { "1234567890", "1234567890" }));
+        assertEquals(132L, MemoryUtil.sizeOf(Lists.asList("1234567890", new String[] { "1234567890" })));
+        assertEquals(132L, MemoryUtil.sizeOf(Maps.map("1234567890", "1234567890").$()));
+    }
+
+    private long getObjectSize(Object value) {
+        System.setProperty("java.vm.name", "Java HotSpot(TM) ");
+        return ObjectSizeCalculator.getObjectSize(value);
+    }
 }
\ No newline at end of file