When I did the last one a while ago, I just measure the area as has been said, you should be roughly the same amount,
The most important thing is to cut and lay the longest first, and work down to the shortest, After you've laid about
30% you ought to be able to start using the rather large pile of offcuts you have made!
Obviously when you have laid the first half, you will know exactly.
HTH Regards Rodders