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Times are a guide and ovens vary; the thermometer reading is what matters. Take the joint out of the fridge 30 to 60 minutes before cooking, and rest it loosely covered in foil before carving.
What The Roast Beef Cooking Time Calculator Works Out
- Cooking time: the classic UK timings for topside, sirloin or rib by weight and doneness at 180C fan: 20 minutes per 450g plus 20 for rare, 25 plus 25 for medium, 30 plus 30 for well done, rounded to the nearest 5 minutes. A 1.8kg joint is about 1 hr 45 min for medium.
- Doneness temperatures: around 52C for rare, 60C for medium and 70C for well done before resting; the reading climbs a few degrees as it rests. Beef needs a proper 30-minute rest, which also makes carving far easier.
- Resting time: the minimum rest before carving (30 minutes here). Resting lets the juices settle back through the meat, and a rested joint stays hot for far longer than you would expect, so it is part of the timing rather than extra.
- Target temperature: the internal reading in the thickest part, away from bone, that means the joint is done. The thermometer is the reliable test; the clock is only the plan.
- Serving-time plan: enter a time to eat and the calculator counts backwards through resting, cooking, preheating and the time out of the fridge, giving a clock time for each step.
- Oven type (advanced): the standard guidance is written for 180C fan; a conventional oven runs about 20C hotter for the same result (200C) and gas mark 6 is the equivalent. The time does not change, only the dial setting shown.
- Bone-in and stuffed (advanced): bone slows heat reaching the centre, so bone-in joints get about 10% longer; stuffing adds roughly 20 minutes (weigh a stuffed bird after stuffing). Both are rules of thumb, which is another reason to trust the thermometer.
- Serves and weight to buy (advanced): raw weight per person of about 250g boneless or 350g bone-in, so the calculator tells you how many a joint feeds and how big a joint to buy for your table.
- Take out of the oven at (advanced): red meat keeps cooking while it rests and rises around 4C, so pull it a few degrees under target. Poultry must reach the full 75C before it comes out; there is no carry-over allowance for chicken.
- Hot start (advanced): 25 minutes at 220C fan before turning down builds a crust on beef and lamb and is the standard route to pork crackling. Keep the overall time the same; the plan adds a "turn the oven down" step.
- Total from fridge to table (advanced): tempering time plus cooking plus resting, which is the figure to plan the day around. Times here are a guide; ovens vary, so check early rather than late.
Source and further reading: Food Standards Agency: cooking safely.