im using a bathtub it measures out to about 28" x 50". It's got 7' ceiling but I ve got a huge filtercan up top taking up ~20". I can fit 3 15 gals or 4 10's. Im not growing for yield so i dont jam it full. I usually grow 1-3 plants at a time. I can yield 8z off of 1 good grower in a 10gal. I have very high ppfd. i grow in soil. I veg my plants out to a good size and train them relentlessly, (to be bushy)`. Here's a pic of 3 ladies, day 12, 12/12. i think there is a 5 a 10 and 15 gal in that pic. These had been outside and needed to be inconspicuous. i coudlnt use all 15's because of fear of detection.
View attachment 3774182
EDIT: in these pics the pots aren't cut, rather they are partially filled. I fill the pots 2/3-3/4 usually if i know it's gonna be a stocky indica I might fill it up