Prime Rib for 10 to 100 guests
Standard scenario: adults, average appetites, two or three sides on the table. The "at the counter" column rounds up to pieces you can actually buy.
| Guests | Cooked meat | Raw to buy | At the counter |
|---|---|---|---|
| 10 | 4 lb | 5.5–6 lb | one ~6.5-lb bone-in rib roast (≈6.5 lb) |
| 20 | 8 lb | 10.5–12.5 lb | one ~12.5-lb bone-in rib roast (≈12.5 lb) |
| 25 | 10 lb | 13.5–15.5 lb | one ~15.5-lb bone-in rib roast (≈15.5 lb) |
| 50 | 20 lb | 27–31 lb | two ~15.5-lb bone-in rib roasts (≈31 lb) |
| 100 | 40 lb | 53–62 lb | four ~15.5-lb bone-in rib roasts (≈62 lb) |
The yield: raw pound ≠ served pound
A bone-in rib roast gives up weight to the bones (about a pound each) and to cook shrink, though a gentle low-temperature roast keeps shrink modest. Figure 65–75% of raw bone-in weight ends up as servable meat.
Prime rib portions run richer than the ⅓-lb baseline — people take a thick slice. Plan ~0.4 lb cooked per adult with sides, 0.6 lb when it’s the centerpiece; the old butcher’s rule of one bone per two guests lands in the same place.
Buying prime rib: what to look for
Figure roughly 2¼ lb per bone: a 3-bone roast (~7 lb) serves six to eight, a full 7-bone roast (~16 lb) feeds a holiday table. Ask for the chine bone cut and the ribs tied back on — bones make a natural roasting rack and carve away cleanly. "Prime rib" is the roast’s name, not its grade; Choice with good marbling eats beautifully.
Frequently asked questions
How much prime rib per person?
0.4 lb of cooked prime rib per adult when two or three sides share the table, 0.6 lb for hearty appetites or a meat-centered meal; kids about half. Since prime rib keeps only 65–75% of its raw weight, that's roughly 0.53–0.62 lb raw per adult. Prime rib portions run richer than the ⅓-lb baseline — people take a thick slice. Plan ~0.4 lb cooked per adult with sides, 0.6 lb when it’s the centerpiece; the old butcher’s rule of one bone per two guests lands in the same place.
How much prime rib for 20 people?
About 10.5–12.5 lb raw for 20 adults with a normal spread of sides — at the counter, one ~12.5-lb bone-in rib roast (≈12.5 lb). Scale with the chart above or the calculator for your exact crowd.
Why buy so much more raw prime rib than you serve?
A bone-in rib roast gives up weight to the bones (about a pound each) and to cook shrink, though a gentle low-temperature roast keeps shrink modest. Figure 65–75% of raw bone-in weight ends up as servable meat.
What internal temperature is prime rib safe at?
USDA calls whole-muscle beef safe at 145°F with a 3-minute rest; prime rib is usually served below that at medium-rare, a normal and widely accepted choice for intact whole-muscle roasts. Doneness details and hour-per-pound charts are on the prime rib cook-time page.
How many bones do I need?
One bone per two hearty eaters is the classic rule — each bone carries about 2¼ lb of roast. A 4-bone roast (~9 lb) comfortably serves eight with sides.