Hi from Downunder in Australia.
It is a bit hard to tell how much fabric you need without some idea of what you are making. Do you have a picture, finished dimensions of the quilt, web link - anything.
12yards "probably" sounds about right but much will vary with your design and layout.
Assuming that you mean 16" finished blocks you will need to cut blocks for hand applique bigger and trim after all that handling, so allow about 18" squares. So you will get 4 per yard, and for 25 you will need you will need 6 1/2 yards. That is just for the blocks.
You don't say how wide your borders are so I will just assume that they are 8" finished, and that you can get four strips across the width of the fabric. For Borders you will need the length of your quilt so you can cut all borders across one width of fabric - in this case about another 3yards if you have sashing between your blocks -
because - most baltimore layouts have sashing between the blocks, and you haven't mentioned how wide they are. Sashes will add to the fabric you need for your borders by making your quilt longer and wider. Sashes (with contrast squares, so not cut in one long piece) 2" wide will take just under 2 yards.
More details needed to be specific, but the last quilt I made that was that big I just bought a 20yard bolt of background fabric and threw what was left over into the stash for another project LOL.