STL files into CURA tiny?

hi there i am pretty new here but have been 3d printing for about 8months .... i have run into this problem with some files in the past but managed to avoid the problem by just finding alternative files from another source but now find the need to figure it out as there are no other good sources for the files i want.

so now the problem is that i have these .STL files that i want to print but when i open them into my slicer(cura) they are just tiny and i dont know how to fix them for printing, i do know how to resize but i dont know the size they should be.... is there a way to fix this or am i just out of luck unless i keep guessing and trying till i get size right? because thats not gonna happen as these are big, long prints like 10hrs+ ...

please help me out and thanks in advance...

Can you see a correlation between the size of the model in "real life" and the size it appears in Cura? Sometimes a model is created in Imperial units, but get loaded in metric. As an example, an eight inch model incorrectly configured will load in as an eight millimeter model. In the reverse situation, a ten millimeter model may load as 254 millimeters.

Consider to use a multiplier of 25.4 when you scale up the model. If it uses percentages, use 2540 as the multiplier.

i cannot see a corralation between the shown size in cura and size it should be on some but others i can see it ... like i have tried to scale 25.4 on them and one seems like it might be correct after that but another becomes just huge ....even the one that appears correct im not sure if it is till i print one but as for the other example i know for sure it becomes way tooo big and i have no idea what else to try as far as scaling it