=IF(SUM(J7)=0,"",ROUNDUP(I13/J7,0)*J7)
=IF(OR(SUM(J7)=0, SUM(I13)=0),"",ROUNDUP(I13/J7,0)*J7)
so does that mean i must have a value in cell j7 at all times otherwise the formula will show a 'DIV' error always?
Yup, since your formula use the value of J7 for division calculation.
also, can the formula in k13 have an if statement that if there is zero or nothing in j7, then show nothing otherwise sum k7 to k12?
see if below is the one you looking for?
=IF(SUM(I13)=0,"",ROUNDUP(I13/ IF(J7=0,1,J7),0)*IF(J7=0,1,J7))
or:
=IF(SUM(I13)=0,"",IF(J7=0,ROUNDUP(I13,0),ROUNDUP(I13/J7,0)*J7))
cell J7 is empty (zero), so you got a divided by zero error.