#CALC! error on Excel

Hi guys,

Help on this would be greatly appreciated.

I would like the column O (RATE) to be blank when there is no value entered in columns K (CWS SIZE) and L (HWS SIZE).

At the moment as you can see in the image, when columns K & L are blank its showing the CALC error in column O.

It's only when a correct value is entered that error message disappears.
Formula:

=MIN(TOCOL(IFS(K7:L7={15;22;28;35;42;54;67;76;89;108},{11.39,11.39;11.68,11.68;11.96,11.96;13.08,15.2;14.02,16.35;15.77,18.22;17.17,19.57;20.62,25.63;24.34,28.59;31.25,36.09}),2))

I'm sure it's a simple fix!

Many thanks,