1 gal 7" OD x 7" high approx, 2 gal 9" OD x 9" high approx, 3.5 gal - 12" OD x 13" high approx, 5 gal 12" od x 15" high approx
I am only using one gal in my next grow unless I decide to use a larger tent - I would need 24" square for 4 3.5 gal's - the Growlab GL40 is 16" square x 47" high & I can only fit the one gals if I want to grow 4 plants, I'm still figuring it out man. I would really love to go with 3.5 for less hassle of adding water tho. I donno man!!!! I hate it XD I don't even know what type of light I should use yet, JasonKanz got me into LED's
Another plus about 3.5 gal & 5 gal is bucket baskets work with them