A tablespoon of coffee weighs approx 14 grams.
1 pound weighs approx 454 grams.
454/14 = approx 32 teaspoons per pound or 32 cups.
If 20% get refills you will need 120 teaspoons or 3.75 or better yet 4 pounds of coffee (just in case 20% was low).
Note all weights are US and all are approximate.