Prime Rib Calculator

How it works

roast weight = guests × 450 g (1 lb) bone-in or 300 g (⅔ lb) boneless (× 1.33 for hearty eaters) · ribs ≈ weight ÷ 0.95 kg (2.1 lb) · classic time = 15 min at 230 °C + weight × 12/14/16 min per lb at 165 °C · reverse sear = weight × 26/30/34 min per lb at 110 °C + 10 min sear

Butchers plan about 450 g (1 lb) of bone-in standing rib roast per person — one rib feeds about two — or 300 g (⅔ lb) boneless. In the classic method the roast is seared at 230 °C (450 °F) for 15 minutes, then roasted at 165 °C (325 °F) for roughly 12, 14 or 16 minutes per pound for rare, medium-rare or medium. A reverse sear cooks low at 110 °C (225 °F) for an even pink interior, then finishes with a short blast of high heat. Times are only estimates: always use a probe thermometer and remove the roast 5–6 °C (10 °F) below the target, because the temperature keeps rising while it rests. USDA recommends 63 °C (145 °F) with a 3-minute rest for whole cuts of beef.

Worked example

For 8 guests with a bone-in roast: 8 × 450 g = 3.6 kg (about 4 ribs). Classic method for medium-rare: 15 min at 230 °C plus 7.9 lb × 14 min ≈ 2 h 6 min at 165 °C in total; take it out at 52 °C (125 °F) and rest it 20–30 minutes to reach 57 °C (135 °F).

Sources: USDA FSIS — Safe minimum internal temperatures · Certified Angus Beef — Prime rib roasting guide

Frequently asked questions