Defect Density = No.of issues Raised/No.of Issued Fixed

defect density is the count of total defects identified 
against a particular software entity

it is calculated as...
no of defects/ size of software
where size is typically counted in lines of code

this is used to compare the relative number of defects in 
various software components, to find out the defect prone 
areas of the application

Defect density = Total number of defects/LOC (lines of code)
Defect density = Total number of defects/Size of the project
Size of Project can be Function points, feature points, use 
cases, KLOC etc

If size is diffecult to find the replace the size with 
Effort spent i.e. # of Defects/Effort Spent.

Defect Density is "amount of defects found in total length
or size of program code"

Defect Density = amount of defects/length or size of program
 code