Find a good bag that has an assortment of food, etc for Lovebirds (even Conure food can help).
If you look at the size and still need more, purchase: Sunflower Seed; Safflower Seed; Cracked Corn; Millet and individually sold food that can be added to your bag of Lovebird food.
You don't always go by the size, but what's in it. Always purchase individuals seeds, like the ones listed above to add on top of the seed you purchase in the bag. I have four Lovebirds. I first sprinkle the Lovebird food from the bag, then I sprinkle on the individual seed listed above, or food I make. You can always add to what's in the bag!