Use the free Roast Beef Quantity Calculator below, right in your browser. No sign-up, no software to install, and nothing is sent to a server.
Roast beef is the centrepiece of many Sunday lunches and holiday meals, and buying the right amount starts with the cut. A bone-in rib roast and a lean fillet are not interchangeable by weight: the rib carries bone and a generous cap of fat, while the fillet is almost pure meat. This calculator adjusts for the cut, the appetite of your guests, and whether you want leftovers, so you buy enough without paying for meat nobody eats.
Bone-in rib is the classic roast for a crowd. Plan on about 500 grams per person for a standard appetite, 400 grams for light eaters, and 650 grams for hearty eaters. The bone and fat add flavour and keep the meat moist, but they also add weight that never reaches the plate, which is why the raw number looks high. Rib is the most forgiving roast for beginners, because its fat protects it from drying out.
Sirloin is a leaner boneless choice, and the numbers drop accordingly: about 300 grams per person for a standard appetite, 250 grams light, and 400 grams hearty. Sirloin has good flavour and a reasonable price, and it carves into neat slices. It dries out faster than rib, so it rewards a thermometer and a proper rest more than extra cooking time, and it should never be cooked far past medium.
Topside is the budget boneless roast, and it needs about 350 grams per person standard, 300 grams light, and 450 grams hearty. It is lean and can turn tough if overcooked, so it suits slow roasting and thin slicing across the grain. Many cooks lard it or bard it with fat, or roast it with the fat cap left on, which helps a great deal. Sliced thinly, topside makes excellent cold sandwiches the next day.
Fillet is the luxury option: tender, lean, and almost free of waste. About 250 grams per person is a standard serving, 200 grams light, and 325 grams hearty. Fillet costs much more per kilo, but because there is nothing to trim and almost no shrinkage beyond moisture loss, the gap between raw and served weight is small. It cooks fast, so watch it closely and pull it a few degrees before your target temperature.
Shrinkage is the part most shoppers forget. A roast loses roughly a quarter to a third of its raw weight during cooking, through moisture loss and fat rendering, and a bone-in roast loses more to the bone. That is why a kilo of raw rib does not feed as many people as a kilo of raw fillet. This calculator already accounts for that difference in its per-person figures, and it shows the expected cooked weight so you can sanity-check the result.
Leftovers are a deliberate choice with roast beef, because cold roast beef is genuinely useful: sandwiches, salads, and stir-fries all welcome it. Adding 25 percent covers a generous round of sandwiches the next day without turning the main meal into a mountain of meat. If you do not want leftovers, skip the extra, since beef is the most expensive meat to waste.
Cooking method matters as much as weight. Sear the outside at high heat first, then roast gently until the centre reaches your target: about 52 degrees for rare, 57 for medium-rare, and 63 for medium, measured with a thermometer in the thickest part. Remember the temperature climbs a few degrees while resting, so pull the roast a little early rather than a little late.
Resting transforms the result. Rest the roast for 20 minutes, loosely tented, before slicing. The juices redistribute through the meat instead of flooding the carving board, and the slices stay moist even if the roast was cooked to the warmer end of your range. Use the time to make gravy from the pan juices and to warm the plates and the Yorkshire puddings.
Slicing technique changes how tender the meat feels. Always slice across the grain, and slice thinly, especially for topside and sirloin. Cutting with the grain leaves long muscle fibres that feel chewy no matter how well the beef was cooked, while thin slices across the grain feel tender even from a lean cut. A sharp carving knife matters more here than an expensive one.
Budget planning follows from the cut choice. Rib costs more per kilo than topside but feeds fewer people per kilo because of the bone, so compare the cost per served portion, not the price on the label. For a large group on a budget, topside or a boneless sirloin often wins. For a special occasion where flavour matters most, rib is hard to beat, and fillet is the choice when tenderness matters most.
To use the calculator, enter your guest count, choose the cut, choose the appetite, and say whether you want leftovers. You will get the raw weight to buy and the expected cooked weight. Buy the joint closest to that weight, cook to temperature rather than to the clock, rest it well, and slice thinly across the grain.
Versión en español: Calculadora de Cantidad de Carne Asada – Peso Crudo por Corte e Invitados