When planning for whole, unfilleted fish (head, tail, and skeleton intact, though gutted and scaled), the standard culinary calculation is approximately 1 pound (16 ounces or about 450 to 500 grams) of raw whole fish per person.
The reason for this number comes down to yield. A whole round fish typically yields between 45% and 50% edible meat once the bones, head, skin, and fins are accounted for. Therefore, purchasing a 1-pound whole fish will give each guest a generous and satisfying portion of about 7 to 8 ounces (roughly 200 to 225 grams) of cooked fish.
For a group of 6 people, you will want to purchase around 6 pounds (approximately 2.7 to 3 kg) of whole fish in total.
Depending on what you are grilling, there are two common approaches. If you are serving individual portion-sized fish (such as trout, branzino, or sea bream), look for 6 individual fish weighing about 1 to 1.25 pounds each. If you prefer to grill one or two larger fish to carve at the table (like red snapper or striped bass), two 3-pound fish or one large 6-pound fish will work equally well. If you have big eaters or are serving lighter side dishes, bumping the estimate up to 1.25 pounds per person is a safe buffer.
