File transfer speed is very low. WinSCP does not utilize all available bandwidth. How do I improve the transfer speed?

When using SSH or TLS/SSL, file transfers in WinSCP are encrypted and encryption is CPU intensive. Either your local machine or your server might not be able to encrypt file transfer stream at the same speed, your connection is able to transfer it.

WinSCP as well as most (if not all) SFTP servers cannot distribute the encryption/decryption among CPU cores, so it’s actually a capacity of a single CPU core that limits the transfer speed.

Use the Windows Task manager to see, if one of the cores is utilized to its maximum during the transfer.

In case the speed is throttled by CPU, it may help if you choose different encryption algorithm on SSH page of Advanced Site Settings dialog (supposing you are using SSH-based file transfer protocol, such as SFTP or SCP). Blowfish is usually a lot faster than AES. It may also help, if you turn off compression, if you have turned it on before.

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Also there’s a lots to improve in performance of WinSCP itself 164. So it may get better in future versions.

Also note that as SSH code of WinSCP is based on PuTTY, file transfers with SSH-based protocols can hardly be faster than PuTTY (PSCP/PSFTP) is. Hence there is no point asking for speed improvements, if you get the same rate with PuTTY.

If WinSCP started being slow suddenly, check if you did not enable logging on “Debug” level inadvertently.