diff --git a/icu4c/source/common/ucmndata.c b/icu4c/source/common/ucmndata.c
index 85afabf1204..0ac16c554fb 100644
--- a/icu4c/source/common/ucmndata.c
+++ b/icu4c/source/common/ucmndata.c
@@ -68,6 +68,7 @@ static uint32_t offsetTOCEntryCount(const UDataMemory *pData) {
 static const DataHeader *
 offsetTOCLookupFn(const UDataMemory *pData,
                   const char *tocEntryName,
+                  int32_t *pLength,
                   UErrorCode *pErrorCode) {
     const UDataOffsetTOC  *toc = (UDataOffsetTOC *)pData->toc;
     if(toc!=NULL) {
@@ -95,6 +96,11 @@ offsetTOCLookupFn(const UDataMemory *pData,
 /*      fprintf(stderr, "Found: %p\n",(base+toc[2*start+1])) */
             fprintf(stderr, "Found it\n");
 #endif
+            if((start+1)<toc->count) {
+                *pLength=(int32_t)(toc->entry[start+1].dataOffset-toc->entry[start].dataOffset);
+            } else {
+                *pLength=-1;
+            }
             return (const DataHeader *)&base[toc->entry[start].dataOffset];
         } else {
 #ifdef UDATA_DEBUG
@@ -124,6 +130,7 @@ static uint32_t pointerTOCEntryCount(const UDataMemory *pData) {
 
 static const DataHeader *pointerTOCLookupFn(const UDataMemory *pData,
                    const char *name,
+                   int32_t *pLength,
                    UErrorCode *pErrorCode) {
     if(pData->toc!=NULL) {
         const PointerTOC *toc = (PointerTOC *)pData->toc;
@@ -148,6 +155,7 @@ static const DataHeader *pointerTOCLookupFn(const UDataMemory *pData,
 
         if(uprv_strcmp(name, toc->entry[start].entryName)==0) {
             /* found it */
+            *pLength=-1;
             return UDataMemory_normalizeDataPointer(toc->entry[start].pHeader);
         } else {
             return NULL;
diff --git a/icu4c/source/common/ucmndata.h b/icu4c/source/common/ucmndata.h
index 3079a4f6785..886ef32055b 100644
--- a/icu4c/source/common/ucmndata.h
+++ b/icu4c/source/common/ucmndata.h
@@ -64,6 +64,7 @@ typedef struct {
 typedef const DataHeader *
 (* LookupFn)(const UDataMemory *pData,
              const char *tocEntryName,
+             int32_t *pLength,
              UErrorCode *pErrorCode);
 
 typedef uint32_t
diff --git a/icu4c/source/common/udata.c b/icu4c/source/common/udata.c
index 47fcecca2b4..e95dc8378c1 100644
--- a/icu4c/source/common/udata.c
+++ b/icu4c/source/common/udata.c
@@ -1074,8 +1074,10 @@ doOpenChoice(const char *path, const char *type, const char *name,
         pCommonData=openCommonData(path, isICUData, &errorCode); /** search for pkg **/
 
         if(U_SUCCESS(errorCode)) {
+            int32_t length;
+
             /* look up the data piece in the common data */
-            pHeader=pCommonData->vFuncs->Lookup(pCommonData, tocEntryName, &errorCode);
+            pHeader=pCommonData->vFuncs->Lookup(pCommonData, tocEntryName, &length, &errorCode);
 #ifdef UDATA_DEBUG
             fprintf(stderr, "pHeader=%p\n", pHeader);
 #endif
@@ -1088,6 +1090,7 @@ doOpenChoice(const char *path, const char *type, const char *name,
                     return NULL;
                 }
                 if (pEntryData != NULL) {
+                    pEntryData->length = length;
                     return pEntryData;
                 }
             }
diff --git a/icu4c/source/common/udatamem.c b/icu4c/source/common/udatamem.c
index 6b39980cc3d..06a5308745b 100644
--- a/icu4c/source/common/udatamem.c
+++ b/icu4c/source/common/udatamem.c
@@ -25,6 +25,7 @@
 
 void UDataMemory_init(UDataMemory *This) {
     uprv_memset(This, 0, sizeof(UDataMemory));
+    This->length=-1;
 }
 
 
@@ -106,6 +107,52 @@ udata_getMemory(UDataMemory *pData) {
     }
 }
 
+/**
+ * Get the length of the data item if possible.
+ * The length may be up to 15 bytes larger than the actual data.
+ *
+ * TODO Consider making this function public.
+ * It would have to return the actual length in more cases.
+ * For example, the length of the last item in a .dat package could be
+ * computed from the size of the whole .dat package minus the offset of the
+ * last item.
+ * The size of a file that was directly memory-mapped could be determined
+ * using some system API.
+ *
+ * In order to get perfect values for all data items, we may have to add a
+ * length field to UDataInfo, but that complicates data generation
+ * and may be overkill.
+ *
+ * @param pData The data item.
+ * @return the length of the data item, or -1 if not known
+ * @internal Currently used only in cintltst/udatatst.c
+ */
+U_CAPI int32_t U_EXPORT2
+udata_getLength(UDataMemory *pData) {
+    if(pData!=NULL && pData->pHeader!=NULL && pData->length>=0) {
+        /*
+         * subtract the header size,
+         * return only the size of the actual data starting at udata_getMemory()
+         */
+        return pData->length-pData->pHeader->dataHeader.headerSize;
+    } else {
+        return -1;
+    }
+}
+
+/**
+ * Get the memory including the data header.
+ * Used in cintltst/udatatst.c
+ * @internal
+ */
+U_CAPI const void * U_EXPORT2
+udata_getRawMemory(UDataMemory *pData) {
+    if(pData!=NULL && pData->pHeader!=NULL) {
+        return pData->pHeader;
+    } else {
+        return NULL;
+    }
+}
 
 UBool  UDataMemory_isLoaded(UDataMemory *This) {
     return This->pHeader != NULL;
diff --git a/icu4c/source/common/udatamem.h b/icu4c/source/common/udatamem.h
index 840e674e0a4..d63d598de29 100644
--- a/icu4c/source/common/udatamem.h
+++ b/icu4c/source/common/udatamem.h
@@ -1,7 +1,7 @@
 /*
 ******************************************************************************
 *
-*   Copyright (C) 1999-2001, International Business Machines
+*   Copyright (C) 1999-2003, International Business Machines
 *   Corporation and others.  All Rights Reserved.
 *
 ******************************************************************************/
@@ -39,6 +39,7 @@ struct UDataMemory {
                                    /* Only non-null if a close operation should unmap */
                                    /*  the associated data, and additional info       */
                                    /*   beyond the mapAddr is needed to do that.      */
+    int32_t           length;      /* Length of the data in bytes; -1 if unknown.     */
 };
 
 UDataMemory     *UDataMemory_createNewInstance(UErrorCode *pErr);