Filter size?

[esim13]

How can I determine my filter size? I'm considering purchasing the PENTAIR DYNAMO 3/4 HP 2 SPEED. So I started looking at my filter size but I can't see any markings to determine it's size. None of the holes are punched at the 16 18 or 22 mark.
Here's a pic of the panel

Thanks!

 

[dmanb2b]

Try measuring from the base to the top of the multiport and then also the width. You may be able to tell based on the clearance measurements they provided.