One cup of Sundays is roughly a pinch over 3 oz by weight or 93 grams.
Therefore, a 40 oz box has roughly 12 cups; a 72 oz box 22 cups; and 144 oz bundle has 44 cups.
Depending on the size of your dog, our 3 main sizes are designed to last 2-4 weeks; with the smallest size 40 oz lasting about 4 weeks for a small dog, and the 144 oz lasting 2 weeks for a very large dog. The 144 oz typically lasts a lab about 4 weeks; the 72 oz box lasts most medium breeds about 4 weeks.
You can get full feeding instructions and estimates here: https://sundaysfordogs.com/howmuch