The starting row of diamonds I used 7 diamonds so my base chain was 71 chains.
Materials I used
I hook ( 5.5mm) you can use any size you chose this was just my favorite, and you don't need an afghan hook it will most likely get in the way.
32 oz Red worsted weight (4) yarn
38 oz Blue worsted weight (4) yarn
24oz Grey worsted weight (4) yarn
This was used to make the afghan with the attached pocket, so you could get away with a bit less for this sized afghan if you don't wish to add the pocket.