Lights in a small area

When figuring square feet per lumens do I use the square feet of the grow closet or the square feet of the plants in the closet? I have 8 square feet of space but the plants are in 6 square feet.

Thank you,

that depends are your plants finished growing and are you going to keep them in the footprint or let them grow into full space because yes you can use the math for your plants not your space