If you wish to feed your betta once daily, i'd suggest feeding 5-7 bloodworms, as they arent overly active, so feeding them too much may cause constipation or make them fat, and with their delicate fins it will be harder for the fish to swim.
If you wish to feed more than once a day, say 2-3 pieces twice daily or 1-2 worms 3-4 times daily.
Minimal amounts of most foods will keep betta's tummy full, with a lower risk or constipation or unnecessary weight gain. Also remember to keep the betta's food selection diverse.
Remember: A betta's stomach is tiny!