interior dimensions for a sump

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I just purchased a 15 gallon high aquarium, but it will not be arriving until next week, I was wondering if someone knew the interior dimensions of this size of a tank, so I can start making the baffles? The LxWxH would be most helpful.

Also is 500 gph too much flow for a 55 gallon aquarium with this 15 gallon sump? I know 300 gph is usually the standard for this size tank

Thanks