diff --git a/sdk/storage/azure-storage-blobs/CHANGELOG.md b/sdk/storage/azure-storage-blobs/CHANGELOG.md
index 09c374db7..906f54a32 100644
--- a/sdk/storage/azure-storage-blobs/CHANGELOG.md
+++ b/sdk/storage/azure-storage-blobs/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### Breaking Changes
 
 - Renamed `HasMorePages()` in paged response to `HasPage()`.
+- Default chunk size for concurrent upload was changed to nullable.
 
 ## 12.0.0-beta.10 (2021-04-16)
 
diff --git a/sdk/storage/azure-storage-blobs/inc/azure/storage/blobs/blob_options.hpp b/sdk/storage/azure-storage-blobs/inc/azure/storage/blobs/blob_options.hpp
index 712a75845..6c4042cfd 100644
--- a/sdk/storage/azure-storage-blobs/inc/azure/storage/blobs/blob_options.hpp
+++ b/sdk/storage/azure-storage-blobs/inc/azure/storage/blobs/blob_options.hpp
@@ -743,7 +743,7 @@ namespace Azure { namespace Storage { namespace Blobs {
        * @brief The maximum number of bytes in a single request. This value cannot be larger than
        * 4000 MiB.
        */
-      int64_t ChunkSize = 4 * 1024 * 1024;
+      Azure::Nullable<int64_t> ChunkSize;
 
       /**
        * @brief The maximum number of threads that may be used in a parallel transfer.
diff --git a/sdk/storage/azure-storage-blobs/src/block_blob_client.cpp b/sdk/storage/azure-storage-blobs/src/block_blob_client.cpp
index eeba8f8f6..1f24a2236 100644
--- a/sdk/storage/azure-storage-blobs/src/block_blob_client.cpp
+++ b/sdk/storage/azure-storage-blobs/src/block_blob_client.cpp
@@ -110,9 +110,26 @@ namespace Azure { namespace Storage { namespace Blobs {
       const UploadBlockBlobFromOptions& options,
       const Azure::Core::Context& context) const
   {
+    constexpr int64_t DefaultStageBlockSize = 4 * 1024 * 1024ULL;
     constexpr int64_t MaxStageBlockSize = 4000 * 1024 * 1024ULL;
+    constexpr int64_t MaxBlockNumber = 50000;
+    constexpr int64_t BlockGrainSize = 1 * 1024 * 1024;
 
-    int64_t chunkSize = std::min(MaxStageBlockSize, options.TransferOptions.ChunkSize);
+    int64_t chunkSize;
+    if (options.TransferOptions.ChunkSize.HasValue())
+    {
+      chunkSize = options.TransferOptions.ChunkSize.Value();
+    }
+    else
+    {
+      int64_t minChunkSize = (bufferSize + MaxBlockNumber - 1) / MaxBlockNumber;
+      minChunkSize = (minChunkSize + BlockGrainSize - 1) / BlockGrainSize * BlockGrainSize;
+      chunkSize = std::max(DefaultStageBlockSize, minChunkSize);
+    }
+    if (chunkSize > MaxStageBlockSize)
+    {
+      throw Azure::Core::RequestFailedException("Block size is too big");
+    }
 
     if (bufferSize <= static_cast<std::size_t>(options.TransferOptions.SingleUploadThreshold))
     {
@@ -172,7 +189,10 @@ namespace Azure { namespace Storage { namespace Blobs {
       const UploadBlockBlobFromOptions& options,
       const Azure::Core::Context& context) const
   {
+    constexpr int64_t DefaultStageBlockSize = 4 * 1024 * 1024ULL;
     constexpr int64_t MaxStageBlockSize = 4000 * 1024 * 1024ULL;
+    constexpr int64_t MaxBlockNumber = 50000;
+    constexpr int64_t BlockGrainSize = 1 * 1024 * 1024;
 
     {
       Azure::Core::IO::FileBodyStream contentStream(fileName);
@@ -209,7 +229,21 @@ namespace Azure { namespace Storage { namespace Blobs {
       }
     };
 
-    int64_t chunkSize = std::min(MaxStageBlockSize, options.TransferOptions.ChunkSize);
+    int64_t chunkSize;
+    if (options.TransferOptions.ChunkSize.HasValue())
+    {
+      chunkSize = options.TransferOptions.ChunkSize.Value();
+    }
+    else
+    {
+      int64_t minChunkSize = (fileReader.GetFileSize() + MaxBlockNumber - 1) / MaxBlockNumber;
+      minChunkSize = (minChunkSize + BlockGrainSize - 1) / BlockGrainSize * BlockGrainSize;
+      chunkSize = std::max(DefaultStageBlockSize, minChunkSize);
+    }
+    if (chunkSize > MaxStageBlockSize)
+    {
+      throw Azure::Core::RequestFailedException("Block size is too big");
+    }
 
     _internal::ConcurrentTransfer(
         0,
diff --git a/sdk/storage/azure-storage-files-datalake/CHANGELOG.md b/sdk/storage/azure-storage-files-datalake/CHANGELOG.md
index c4d6212bd..30c21cce4 100644
--- a/sdk/storage/azure-storage-files-datalake/CHANGELOG.md
+++ b/sdk/storage/azure-storage-files-datalake/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### Breaking Changes
 
 - Renamed `HasMorePages()` in paged response to `HasPage()`.
+- Default chunk size for concurrent upload was changed to nullable.
 
 ## 12.0.0-beta.10 (2021-04-16)
 
diff --git a/sdk/storage/azure-storage-files-datalake/inc/azure/storage/files/datalake/datalake_options.hpp b/sdk/storage/azure-storage-files-datalake/inc/azure/storage/files/datalake/datalake_options.hpp
index 980605859..62e8fda7e 100644
--- a/sdk/storage/azure-storage-files-datalake/inc/azure/storage/files/datalake/datalake_options.hpp
+++ b/sdk/storage/azure-storage-files-datalake/inc/azure/storage/files/datalake/datalake_options.hpp
@@ -571,7 +571,7 @@ namespace Azure { namespace Storage { namespace Files { namespace DataLake {
        * @brief The maximum number of bytes in a single request. This value cannot be larger than
        * 4000 MiB.
        */
-      int64_t ChunkSize = 4 * 1024 * 1024;
+      Azure::Nullable<int64_t> ChunkSize;
 
       /**
        * @brief The maximum number of threads that may be used in a parallel transfer.