diff --git a/icu4c/source/tools/genbrk/genbrk.cpp b/icu4c/source/tools/genbrk/genbrk.cpp
index f2ace11c063..617c20e1e4e 100644
--- a/icu4c/source/tools/genbrk/genbrk.cpp
+++ b/icu4c/source/tools/genbrk/genbrk.cpp
@@ -213,7 +213,7 @@ int  main(int argc, char **argv) {
     //
     //  Read in the rule source file
     //
-    int         result;
+    long        result;
     long        ruleFileSize;
     FILE        *file;
     char        *ruleBufferC;
@@ -228,7 +228,7 @@ int  main(int argc, char **argv) {
     fseek(file, 0, SEEK_SET);
     ruleBufferC = new char[ruleFileSize+10];
 
-    result = fread(ruleBufferC, 1, ruleFileSize, file);
+    result = (long)fread(ruleBufferC, 1, ruleFileSize, file);
     if (result != ruleFileSize)  {
         fprintf(stderr, "Error reading file \"%s\"\n", ruleFileName);
         exit (-1);
diff --git a/icu4c/source/tools/genccode/genccode.c b/icu4c/source/tools/genccode/genccode.c
index 1a110f7cc1e..3c220d55b05 100644
--- a/icu4c/source/tools/genccode/genccode.c
+++ b/icu4c/source/tools/genccode/genccode.c
@@ -290,7 +290,7 @@ writeObjectCode(const char *filename, const char *destdir) {
         char longNames[100];
     } symbolNames;
     FileStream *in, *out;
-    size_t i, entryLength, length, size;
+    DWORD i, entryLength, length, size;
 
     in=T_FileStream_open(filename, "rb");
     if(in==NULL) {
@@ -307,7 +307,7 @@ writeObjectCode(const char *filename, const char *destdir) {
         uprv_strcat(entry, "_dat");
     }
     /* turn dashes in the entry name into underscores */
-    entryLength=uprv_strlen(entry);
+    entryLength=(int32_t)uprv_strlen(entry);
     for(i=0; i<entryLength; ++i) {
         if(entry[i]=='-') {
             entry[i]='_';
@@ -376,7 +376,7 @@ writeObjectCode(const char *filename, const char *destdir) {
         if(length==0) {
             break;
         }
-        T_FileStream_write(out, buffer, length);
+        T_FileStream_write(out, buffer, (int32_t)length);
     }
 
     /* write the symbol table */
diff --git a/icu4c/source/tools/gencnval/gencnval.c b/icu4c/source/tools/gencnval/gencnval.c
index d1f8ec5e67a..5e055c79ed7 100644
--- a/icu4c/source/tools/gencnval/gencnval.c
+++ b/icu4c/source/tools/gencnval/gencnval.c
@@ -988,7 +988,7 @@ allocString(StringBlock *block, const char *s, int32_t length) {
     char *p;
 
     if(length<0) {
-        length=uprv_strlen(s);
+        length=(int32_t)uprv_strlen(s);
     }
 
     /*
@@ -1027,7 +1027,7 @@ compareAliases(const void *alias1, const void *alias2) {
     int result = ucnv_compareNames(GET_ALIAS_STR(*(uint16_t*)alias1), GET_ALIAS_STR(*(uint16_t*)alias2));
     if (!result) {
         /* Sort the shortest first */
-        return uprv_strlen(GET_ALIAS_STR(*(uint16_t*)alias1)) - uprv_strlen(GET_ALIAS_STR(*(uint16_t*)alias2));
+        return (int)uprv_strlen(GET_ALIAS_STR(*(uint16_t*)alias1)) - (int)uprv_strlen(GET_ALIAS_STR(*(uint16_t*)alias2));
     }
     return result;
 }
diff --git a/icu4c/source/tools/genprops/genprops.c b/icu4c/source/tools/genprops/genprops.c
index 1841d7eb270..3c09e197c66 100644
--- a/icu4c/source/tools/genprops/genprops.c
+++ b/icu4c/source/tools/genprops/genprops.c
@@ -208,12 +208,12 @@ main(int argc, char* argv[]) {
 
 U_CFUNC void
 writeUCDFilename(char *basename, const char *filename, const char *suffix) {
-    int32_t length=uprv_strlen(filename);
+    int32_t length=(int32_t)uprv_strlen(filename);
     uprv_strcpy(basename, filename);
     if(suffix!=NULL) {
         basename[length++]='-';
         uprv_strcpy(basename+length, suffix);
-        length+=uprv_strlen(suffix);
+        length+=(int32_t)uprv_strlen(suffix);
     }
     uprv_strcpy(basename+length, ".txt");
 }
diff --git a/icu4c/source/tools/genrb/derb.c b/icu4c/source/tools/genrb/derb.c
index 17d8f33140c..ac6afa712f7 100644
--- a/icu4c/source/tools/genrb/derb.c
+++ b/icu4c/source/tools/genrb/derb.c
@@ -328,7 +328,7 @@ main(int argc, char* argv[]) {
             if (locale) {
                 printCString(out, converter, locale, -1);
             } else {
-                printCString(out, converter, filename, ext - filename);
+                printCString(out, converter, filename, (int32_t)(ext - filename));
                 printString(out, converter, sp, (int32_t)(sizeof(sp)/sizeof(*sp)));
             }
             printOutBundle(out, converter, bundle, 0, pname, &status);
@@ -422,7 +422,7 @@ static void printCString(FILE *out, UConverter *converter, const char *str, int3
         ucnv_toUnicode(defaultConverter, &bufp, bufend, &str, strEnd, 0, 0, &err);
         *bufp = 0;
 
-        printString(out, converter, buf, bufp - buf);
+        printString(out, converter, buf, (int32_t)(bufp - buf));
     } while (str < strEnd);
 }
 
diff --git a/icu4c/source/tools/genuca/genuca.cpp b/icu4c/source/tools/genuca/genuca.cpp
index bef1c536536..f411bda2b45 100644
--- a/icu4c/source/tools/genuca/genuca.cpp
+++ b/icu4c/source/tools/genuca/genuca.cpp
@@ -402,7 +402,7 @@ UCAElements *readAnElement(FILE *data, tempUCATable *t, UCAConstants *consts, UE
     char *endCodePoint = NULL;
     char *spacePointer = NULL;
     char *result = fgets(buffer, 2048, data);
-    int32_t buflen = uprv_strlen(buffer);
+    int32_t buflen = (int32_t)uprv_strlen(buffer);
     if(U_FAILURE(*status)) {
         return 0;
     }
diff --git a/icu4c/source/tools/makeconv/gencnvex.c b/icu4c/source/tools/makeconv/gencnvex.c
index 80455aa8593..3f45d1bda24 100644
--- a/icu4c/source/tools/makeconv/gencnvex.c
+++ b/icu4c/source/tools/makeconv/gencnvex.c
@@ -121,7 +121,7 @@ CnvExtWrite(NewConverter *cnvData, const UConverterStaticData *staticData,
         _MBCSHeader header={ { 0, 0, 0, 0 }, 0, 0, 0, 0, 0, 0, 0 };
 
         /* write the header and base table name for an extension-only table */
-        length=uprv_strlen(extData->ucm->baseName)+1;
+        length=(int32_t)uprv_strlen(extData->ucm->baseName)+1;
         while(length&3) {
             /* add padding */
             extData->ucm->baseName[length++]=0;
diff --git a/icu4c/source/tools/makeconv/makeconv.c b/icu4c/source/tools/makeconv/makeconv.c
index 6ac853d5deb..7436d448066 100644
--- a/icu4c/source/tools/makeconv/makeconv.c
+++ b/icu4c/source/tools/makeconv/makeconv.c
@@ -411,7 +411,7 @@ int main(int argc, char* argv[])
 
                 else
                 {
-                    T_FileStream_write(q, msg, uprv_strlen(msg));
+                    T_FileStream_write(q, msg, (int32_t)uprv_strlen(msg));
                     T_FileStream_close(q);
                 }
             }
diff --git a/icu4c/source/tools/pkgdata/make.c b/icu4c/source/tools/pkgdata/make.c
index 7ef0b5a2d13..c992eccfded 100644
--- a/icu4c/source/tools/pkgdata/make.c
+++ b/icu4c/source/tools/pkgdata/make.c
@@ -98,7 +98,7 @@ pkg_mak_writeStanza(FileStream *f, const UPKGOptions *o,
                     CharList* parents,
                     CharList* commands )
 {
-    T_FileStream_write(f, target, uprv_strlen(target));
+    T_FileStream_write(f, target, (int32_t)uprv_strlen(target));
     T_FileStream_write(f, " : ", 3);
     pkg_writeCharList(f, parents, " ",1);
     T_FileStream_write(f, "\n", 1);
@@ -117,7 +117,7 @@ pkg_mak_writeFooter(FileStream *f, const UPKGOptions *o)
 {
     char buf[256];
     sprintf(buf, "\n\n# End of makefile for %s [%s mode]\n\n", o->shortName, o->mode);
-    T_FileStream_write(f, buf, uprv_strlen(buf));
+    T_FileStream_write(f, buf, (int32_t)uprv_strlen(buf));
 }
 
 #else   /* #ifdef WIN32 */
diff --git a/icu4c/source/tools/pkgdata/pkgdata.c b/icu4c/source/tools/pkgdata/pkgdata.c
index 6ee3b6d4ce6..a74b6d4dbec 100644
--- a/icu4c/source/tools/pkgdata/pkgdata.c
+++ b/icu4c/source/tools/pkgdata/pkgdata.c
@@ -251,8 +251,8 @@ main(int argc, char* argv[]) {
     }
 
     o.shortName = options[0].value;
-    /**/ {
-        int len = uprv_strlen(o.shortName);
+    {
+        int32_t len = (int32_t)uprv_strlen(o.shortName);
         char *csname, *cp;
         const char *sp;
 
@@ -479,7 +479,7 @@ static void loadLists(UPKGOptions *o, UErrorCode *status)
     
     strcpy(pkgPrefix, o->shortName);
     strcat(pkgPrefix, "_");
-    pkgPrefixLen=uprv_strlen(pkgPrefix);
+    pkgPrefixLen=(int32_t)uprv_strlen(pkgPrefix);
     for(l = o->fileListFiles; l; l = l->next) {
         if(o->verbose) {
             fprintf(stdout, "# Reading %s..\n", l->str);
diff --git a/icu4c/source/tools/pkgdata/pkgtypes.c b/icu4c/source/tools/pkgdata/pkgtypes.c
index 5a114266821..99219a0f4f8 100644
--- a/icu4c/source/tools/pkgdata/pkgtypes.c
+++ b/icu4c/source/tools/pkgdata/pkgtypes.c
@@ -51,10 +51,10 @@ const char *pkg_writeCharListWrap(FileStream *s, CharList *l, const char *delim,
                     uprv_strcat(buffer, "\"");
                 }
             }
-            T_FileStream_write(s, buffer, uprv_strlen(buffer));
+            T_FileStream_write(s, buffer, (int32_t)uprv_strlen(buffer));
         }
 
-        ln  += uprv_strlen(l->str);
+        ln += (int32_t)uprv_strlen(l->str);
 
 		ol = l;
 
@@ -62,9 +62,9 @@ const char *pkg_writeCharListWrap(FileStream *s, CharList *l, const char *delim,
         {
             if(ln > 60 && brk) {
                 ln  = 0;
-                T_FileStream_write(s, brk, uprv_strlen(brk));
+                T_FileStream_write(s, brk, (int32_t)uprv_strlen(brk));
             }
-            T_FileStream_write(s, delim, uprv_strlen(delim));
+            T_FileStream_write(s, delim, (int32_t)uprv_strlen(delim));
         }
         l = l->next;
     }
@@ -103,12 +103,12 @@ const char *pkg_writeCharList(FileStream *s, CharList *l, const char *delim, int
                     uprv_strcat(buffer, "\"");
                 }
             }
-            T_FileStream_write(s, buffer, uprv_strlen(buffer));
+            T_FileStream_write(s, buffer, (int32_t)uprv_strlen(buffer));
         }
         
         if(l->next && delim)
         {
-            T_FileStream_write(s, delim, uprv_strlen(delim));
+            T_FileStream_write(s, delim, (int32_t)uprv_strlen(delim));
         }
         l = l->next;
     }