Hi, it looks like you are a night owl, too. My math skills are not the best, but I'll try to help....I have a reference book. lol
A twin size mattress TOP measures 39 x 75 inches. Add a 10 inch drop (so it drapes over the sides) and that would be 59 x 85 inches. Add another 10 inches if you want it to tuck over the pillow on a bed and that equals 59 x 95. Let's say you want the 59 x 85 option......
So - if your patched piece is 6 inches - 6 goes into 59 nearly 10 times
6 goes into 85 14 times = 10 times 14 = 140 -this means you need 140 6 inch pieces.
If you want to add a 1 inch sashing - lol - the term is sashing - lol - figure that by subtracting 11 inches from the width - 59 minus 11 equals 48
then subract 15 inches from the length - 85 minus 15 equals 70
Now you need to divide 48 inches wide by 6 - equals 8
and 70 inches divided by 6 equals (well it equals 11.6) better make it 12! lol
Now figure 8 times 12 equals 96. you need to make 96 of the 6 inch pieces.
I usually have to make a quick little drawing of the rows to help me count and figure this kind of stuff out ! I got straight A's in art classes but an F in algebra. There may be a simpler method and I'm sure other members of the message board will jump in with suggestions, but this should be in the ball park. I hope it helps.
I used the amounts of 11 inches and 15 inches for the sashing because you need to account for above and below the first and last rows on the length of the quilt ....and you have to account for before and after the first and last rows on the width, too.
To add a border, use the same formula and subtract the width of the border from the width and length and divide the new measurements by 6 to calculate the new total number of 6 inch blocks needed. The wider the border .... the fewer blocks to make..... :D
Just enjoy the process ... don't rush ... and try not to make deadlines and promises that put you under so much pressure that you can't enjoy your hobby. Have a good night (I guess that would be morning - it is 3 am here)