There is a "torpedo space" value in the lower right of the gun menu in the shipyard.
Counted into this get torps that are not inside the launchers, eg. a 4x launcher can load 4 torps which do not show up in this torpspace-value.
However, you can not load to the full torpspace, usually you can load one torp less than it tells you.
A screenshot of your shipyard with gunmenu open would help alot :)
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