DT to Sump gallon ratio?

[donwilson]

I'm looking to build a 90 gallon (maybe more, maybe less) tank and I'm cyphering on how large (in gallons) the sump should be. I'm going to have a standard inflow (skimmer), middle area is refugium, and last section is outflow (back to tank). I was thinking about 30 gallons for the 75, is that about right?

[HndMafia]

use RC's sump calculator (http://reefcentral.com/index.php/sump-volume) on the front page.

FWIW, I'm running a really small sump (45g max before flood) on my 210 due to lack of space, but I had it custom made and worked on the design for awhile before it was built

[peppie]

As large as the space in you stand will hold IMO