1. You need to download and install 7-zip
2. Select the folder that you want to create .tar.gz archive (in my example folder name is "istanbul"). Right click then select "7-Zip" -> "Add to Archive".

3. Choose "Tar" option from the Archive Format menu to create .tar archive

4. Right click your newly created archive (istanbul.tar) then select "7-Zip" -> "Add to Archive" from the menu again to convert your tar archive to .tar.gz. Choose "Gzip" as the "Archive Format".

Note: For maximum compression you can choose "Ultra" for the "Compression Level" and select "258" for the "Word Size"