How big should fuge be?

[Jivatma]

Setting up my first sump. Its a custom 40b with baffles. I have enough material in my kit for 3 sections (plus socks). The plan was to run return drain section with skimmer (on egg crate most likely for water depth), second section as fuge/copepod/time-out, or as just live rock if nothing else.

How big should the minimum be? Further, how big should return section be? I really don't know if I want to mess with an ATO right now. As it is right now.

1st section w/ skimmer (with sock chamber) - 18"D x 16"W x 15"H
2nd section (fuge,etc) - 18"D x 10"W x 10"H
3rd section (return) - 18"D x 10"W x ?H

Am I on the right trail of thinking/mathing?

 

[Bouncingsoul39]

The total volume of the sump area should be about 20% of the display tank volume at a minimum. So yours would need at least 8 gallons of space whatever those dims are i’ll let you calculate.

 

[Jivatma]

The total volume of the sump area should be about 20% of the display tank volume at a minimum. So yours would need at least 8 gallons of space whatever those dims are i’ll let you calculate.

With the current measurements, the second section would come out to just a tad over 8 gal.

3rd section would also be 8ish if filled to the top of the baffle since theyre same size. How small would return section have to be for me to start having to really pay attention to evaporation?