its around 23 x 14. it depends how tou insulate. I'd you just sheet rock you only loose half inch each wall. i choose to fill wall m as with cwllelous and then put 2" rigid insulation on front and back wall. 20 I lost 6" on interior lenght. I hated a extra sheet of rock ov we r dividing wall for sound proof. the long wall was already rocked, insulated and windows trimmed. so I choose to leave it as is, bit could have added 2" there too. instead, I doubled ceiling insulation by blowing callous up there, as was pressed for time.. when I resided front wall I added 1/4" rigid insilation before residing..

I had responded from my phone and autoytpe misspell. Cellulose Insulation was misspelled . The word hated should be installed. .