is a 6 qt box too small?

6qt. sterilite box, im wondering if theat will suffice for a plant. im planning on throwing it into flowering early, but im looking at some pics of mature plants and the roots are massive. im not sure if the 6 qt will be able to handle it. if not, how hard is a transplant to a bigger bucket?

yeah 6qt (1.5gal) is not that much room for some roots.
Depends on what your growing in and what your transferring into, to determine difficulty.
If it's a plant pot or basket with holes in the bottom then you could just cut a hole in a 5gal bucket lid
and slide the pot down in there. Then the roots will just keep growing out of the holes.
If it's a solid bucket and you need to pull the plant, roots and all, to transplant it may be a lil more difficult.
Don't really have experience doing a complete transplant. I'm sure somebody will be able to help.