Roasting is mostly arithmetic: time by weight, then a proper rest. Put in the weight of your joint and when you want to eat, and the calculator works out when it goes in the oven.
Roasting times by weight
| Joint | Oven | Time | Rest |
|---|---|---|---|
| Leg of lamb on the bone, medium | 180°C, fan 160°C, gas 4 | 25 min per 500g, plus 25 min | 20 to 40 min |
| Leg of lamb on the bone, well done | 180°C, fan 160°C, gas 4 | 30 min per 500g, plus 30 min | 20 to 40 min |
| Boneless leg of lamb | 180°C, fan 160°C, gas 4 | 30 min per 500g, plus 30 min | 20 to 40 min |
| Lamb shoulder, slow-roast | 170°C, fan 150°C, gas 3, covered with foil | 40 min per 500g, plus 25 min | 20 to 40 min |
| Whole chicken | 190°C, fan 170°C, gas 5 | 20 min per 500g, plus 25 min | 10 to 15 min |
For lamb shoulder, take the foil off halfway through so the outside browns. For a pull-apart shoulder, keep going: see our slow-roast lamb shoulder.
Worked examples
| Joint | 1.5kg | 2kg | 2.5kg |
|---|---|---|---|
| Lamb leg, medium | 1 hr 40 min | 2 hr 5 min | 2 hr 30 min |
| Lamb leg, well done | 2 hr | 2 hr 30 min | 3 hr |
| Whole chicken | 1 hr 25 min | 1 hr 45 min | 2 hr 5 min |
Is it done?
Ovens vary, so check before you take it out. A meat thermometer is the surest way. Push it into the thickest part, away from the bone.
- Lamb, medium: 60 to 65°C. Without a thermometer, push in a skewer: the juices should be pink and rosy.
- Lamb, well done: the juices run clear and there's no pink left.
- Chicken: at least 75°C in the thickest part of the thigh, with clear juices and no pink meat. Chicken is never served pink.
Why resting matters
While a joint rests, loosely covered with foil, the juices settle back into the meat. Carve it straight away and they end up on the board instead. The meat keeps cooking a little as it rests, so it won't go cold.
Tips for a better roast
- Take the meat out of the fridge 30 minutes to an hour before roasting so it cooks evenly.
- Sit the joint on thick slices of onion. It lifts the meat out of the fat and gives you the start of a gravy.
- Use the fan setting's lower temperature. Fan ovens cook faster at the same number.
- Opened out flat (spatchcocked), a whole chicken roasts in 45 to 50 minutes at 200°C. We'll do it for you at the counter.
Sources: lamb times and temperatures from Waitrose roast lamb guide; chicken times from Morrisons roast chicken guide; 75°C from safefood.