By Linda Garrould · Updated 7 August 2026
The reliable rule for a leg of lamb is 25 minutes per 500g plus 25 minutes for medium, or 30 minutes per 500g plus 30 minutes for well-done, in an oven set to 180°C (160°C fan, gas mark 4) — no separate searing stage needed. But the formula changes depending on the cut: a whole, bone-in leg can safely be served with a blush of pink in the middle, because contamination on an intact joint sits on the surface, where the heat of roasting reaches it. A boneless or rolled leg must be cooked all the way through, like mince, because rolling can fold surface bacteria into the centre of the joint. Set the weight and cut below and the timer does the arithmetic, including a countdown that works backwards from the time you want to sit down.
Boneless and rolled legs are cooked through regardless of the doneness picked above, for the same reason as rolled beef: rolling can carry surface bacteria into the centre of the joint.
Cooked, safely: The thickest part of the leg, away from the bone, should read 60°C at your chosen doneness — Waitrose’s whole published band for lamb runs 60 to 65°C for medium to medium-well, so that’s as far as this tool goes (no “rare lamb” figure is offered). A boneless or rolled leg must be cooked through — the same rule as rolled beef: use the toggle below.
Take the joint out of the fridge 30–60 minutes before roasting, pat it dry, and let a properly preheated oven do the rest. The timer below is your guide — the thermometer is the final word.
Leg of lamb cooking times by weight
The timer above and the chart below use exactly the same figures, worked out at 180°C conventional / 160°C fan / gas mark 4 throughout — unlike beef, there’s no separate high-heat searing stage for lamb. Medium gives you that traditional blush of pink; well-done and boneless/rolled joints use the same, longer formula, because both must be cooked all the way through.
| Weight | Medium (bone-in only) | Well-done / boneless | Serves (approx.) |
|---|---|---|---|
| 1.5 kg | 1 hr 40 min | 2 hr 0 min | 6–7 |
| 2 kg | 2 hr 5 min | 2 hr 30 min | 9–10 |
| 2.5 kg | 2 hr 30 min | 3 hr 0 min | 11–12 |
| 2.75 kg | 2 hr 43 min | 3 hr 15 min | 12–13 |
| 3 kg | 2 hr 55 min | 3 hr 30 min | 13–15 |
| 3.5 kg | 3 hr 20 min | 4 hr 0 min | 16–17 |
The serving figures use a commonly cited rule of thumb of roughly 200–225g of raw, bone-in lamb per person — treat it as a starting point rather than an exact science, since the ratio of bone to meat varies from leg to leg and appetites vary rather more. A 2–2.5kg leg is the everyday Sunday-lunch size for most households; anything over about 2.75kg is worth the longer rest below.
Bone-in or boneless? Why the safety rule is different
This is the one thing about roasting a leg of lamb that’s worth understanding properly, because it changes both the time and the target you’re cooking to. A whole, intact, bone-in leg can safely be served pink in the middle. The reasoning is straightforward: any surface bacteria on a joint of meat sits, unsurprisingly, on the surface, and the outside of a roasting joint comfortably reaches a searing, bacteria-killing heat long before the centre does. The middle of an intact joint is presumed sterile, so cooking it to a lower, pinker temperature is a recognised and safe way to eat lamb.
A boneless or rolled leg is a different matter entirely. To bone and roll a joint, the butcher’s knife has been over the meat’s surface — the very place any bacteria live — and then that surface is folded into the centre of the roll. What was safely on the outside is now, potentially, in the middle. From that point on the joint has to be treated exactly like mince or sausages: cooked all the way through, with no pink remaining. It isn’t a matter of taste or tradition; it’s the reason the well-done and boneless figures in the chart above are identical, and it’s why the timer’s “bone-in or boneless?” toggle forces the longer time the moment you switch it.
If you’re not sure which you’ve bought, ask: a whole leg with the bone still in looks unmistakably like a leg, tapering to the shank; a boneless or rolled joint is netted or tied into a neat cylinder. When in doubt, treat it as boneless — the safer assumption costs you a little time, not your Sunday.
Doneness and temperature: why there’s no “rare” option
The thickest part of the leg, away from the bone, should read 60°C for medium, or 65°C for medium-well on a probe thermometer — the bottom and top of the one temperature band Waitrose publishes for a home-cooked leg of lamb (60 to 65°C for medium to medium-well), which is why the timer offers three settings — medium, medium-well and well-done — and no “rare”. Restaurant kitchens do serve lamb rarer than this, but that relies on specific butchery, provenance and handling that a published, general-audience figure can’t responsibly assume, so we’ve stuck to the two settings that are properly sourced rather than inventing a rare figure that sounds more adventurous than it is.
If you don’t own a thermometer, a decent instant-read model removes the guesswork entirely, for lamb as much as for the Sunday chicken. You can browse instant-read food thermometers on Amazon here. (As an Amazon Associate we earn from qualifying purchases, at no extra cost to you.)
Resting: why the joint keeps cooking after it leaves the oven
Rest the joint for 20 minutes generally, or up to 40 minutes for a larger leg (above roughly 2.75kg), loosely tented with foil. Two things are happening while it sits. First, the muscle fibres, which have tightened and pushed their juices towards the centre under heat, relax again — carve straight from the oven and those juices run out onto the board rather than staying in the meat. Second, there’s carryover cooking: the outer layers of the joint are hotter than the centre when it comes out, and that heat continues to move inward for some minutes afterwards, gently finishing the very centre of a large leg even once it’s off the heat. A joint this size holds its warmth well under foil, so there’s no need to rush the rest to keep lunch hot — and it’s useful cover for finishing the gravy and getting the roast potatoes their turn in a freed, hotter oven.
Carving a leg of lamb
Carve on a board with a groove to catch the juices, and let the joint rest bone-side down if it still has the bone, which makes the anatomy easier to read. For a bone-in leg, find the shank bone and slice down towards it at a slight angle, working parallel slices off one side, then turn the joint and work the other side the same way; the meat around the pelvis end carves in smaller, angled pieces. A boneless, rolled joint is simpler: remove any string, then carve straight across into rounds of whatever thickness you prefer. Either way, a sharp carving knife matters more than a fancy one — a blunt blade tears the meat rather than slicing it, which loses you juices you’ve just spent twenty minutes resting to keep.
Tips for the best roast lamb
- Classic aromatics, simply used. Rosemary, garlic and anchovy are the traditional pairing for a reason: slit the skin in a few places and push in slivers of garlic and small sprigs of rosemary, or work a paste of crushed garlic, rosemary and a little oil over the joint before it goes in. Anchovy fillets tucked into the same slits melt away entirely, leaving savoury depth rather than any fishiness.
- Let it come to room temperature. Half an hour to an hour out of the fridge before roasting means the joint cooks more evenly, so the outside isn’t overdone by the time the centre reaches temperature.
- Lift it off the base of the tin. Sit the leg on a trivet, a rack, or simply a thick bed of sliced onion and root vegetables, so hot air reaches the underside and the vegetables underneath catch all the meat juices — the beginnings of a proper gravy.
- Season generously, and ahead of time if you can. Salt the surface at least an hour before roasting, or the night before if you’re organised; it seasons the meat properly rather than sitting on the surface.
- Don’t skip the rest. It’s covered above in full, but it bears repeating: a beautifully timed joint carved straight from the oven still eats worse than a slightly-less-perfect one that’s rested properly.
Some lamb cooks prefer a slower, gentler alternative — roasting a leg for several hours at a much lower temperature until it’s soft enough to pull rather than carve, the way you might treat a shoulder. It’s a genuinely good method if that’s the texture you’re after, but it uses a different formula entirely to the FSA and Waitrose figures this timer is built on, so we haven’t included specific slow-roast times here; treat it as a different recipe for another day rather than a setting on this tool.
What to serve with roast lamb
Mint sauce is the classic pairing for a reason — its sharpness cuts through the richness of the meat — and a spoonful of redcurrant jelly alongside does something similar with a little more sweetness; both are entirely a matter of taste rather than obligation. Beyond the classics, roast lamb sits happily with roast potatoes, a green vegetable, and the gravy made from the pan juices left behind by the vegetables it roasted on. If you’d like a fuller recipe rather than the timing rule alone, our leg of lamb with garlic and rosemary recipe and roast lamb with thyme and spring vegetables both build on the same basic timings. To get everything — potatoes, vegetables, gravy and the joint itself — onto the table at the same moment, work backwards from your serving time using the planner above, and start the potatoes when the lamb goes in to rest.
More kitchen timers
If you found this useful, the rest of our one-tap kitchen timers take the guesswork out of the other joints and the smaller jobs too: the roast chicken timer for a whole bird done to 75°C, the roast beef timer for topside and sirloin from rare to well-done, the pork loin timer for crackling done properly, and the dippy egg timer and poached egg timer for the smaller jobs at the other end of the meal.
Frequently asked questions
How long do you cook a leg of lamb per kg?
At 180°C conventional / 160°C fan / gas 4, allow 25 minutes per 500g plus 25 minutes for medium, 27.5 minutes per 500g plus 27.5 minutes for medium-well, or 30 minutes per 500g plus 30 minutes for well-done. So a 2kg bone-in leg takes about 2 hours 5 minutes for medium, 2 hours 18 minutes for medium-well, and a 2kg boneless or well-done joint takes about 2 hours 30 minutes.
What time should I put a leg of lamb in the oven to eat at 1pm?
Work backwards. For a 2.5kg bone-in leg cooked to medium — about 2 hours 30 minutes in the oven at 180°C, plus 20 minutes’ rest — it goes in at around 10:10 to be carved at one o’clock. For a different weight, cut or serving time, the timer at the top of this page does the subtraction for you.
Is it safe for lamb to be pink in the middle?
Yes, for a whole, intact, bone-in leg. Surface bacteria stays on the surface, and roasting comfortably reaches a safe temperature there long before the centre does, so a pink centre on an intact joint is considered safe at 60–65°C. A boneless or rolled leg is different — the boning and rolling process can carry surface bacteria into the middle of the joint, so it needs to be cooked all the way through with no pink remaining, exactly like mince.
Do I need to cook a boneless leg of lamb differently to a bone-in one?
Yes. A boneless or rolled leg must be cooked all the way through rather than served pink, because the rolling process can fold surface bacteria into the centre. It uses the same, longer formula as a well-done bone-in leg — 30 minutes per 500g plus 30 minutes — and the timer’s “bone-in or boneless?” toggle switches to this automatically.
What internal temperature should roast lamb be cooked to?
60°C for medium or 65°C for medium-well at the thickest part of the leg, away from the bone — the bottom and top of the one band Waitrose publishes for a home-roasted leg (60 to 65°C for medium to medium-well), which is why this timer doesn’t offer a rare setting. A boneless or rolled joint should show no pink and read hot and cooked through, with no specific lower temperature relied upon.
Is there a setting between medium and well-done?
Yes — medium-well, which the timer offers as a middle option: about 27.5 minutes per 500g plus 27.5 minutes, targeting roughly 65°C at the centre. It sits exactly halfway between Waitrose’s published medium (25 minutes per 500g plus 25, 60°C) and well-done (30 minutes per 500g plus 30) figures, using the top of the same 60–65°C band Waitrose gives for medium to medium-well. Like medium, it only applies to an intact, bone-in leg.
How long should a leg of lamb rest before carving?
Around 20 minutes for an everyday leg, up to 40 minutes for a larger one over about 2.75kg. Resting lets the juices redistribute through the meat instead of running out onto the board, and carryover heat continues gently cooking the very centre of a large joint even once it’s out of the oven.
Should I use a fan oven or a conventional oven for roast lamb?
Either works with the same timings — 180°C conventional or 160°C fan, both gas mark 4. The roasting time is identical; only the temperature dial changes depending on your oven type.
How many people does a leg of lamb serve?
As a rough guide, allow 200–225g of raw, bone-in lamb per person. On that basis a 2kg leg serves roughly 9–10 and a 2.5kg leg serves roughly 11–12, though the bone-to-meat ratio varies between legs, so treat it as a starting point rather than a precise figure.
Do I need to adjust the time if the leg is stuffed?
Adding extra time for a stuffed joint is a common rule of thumb elsewhere, but it isn’t a figure the Food Standards Agency or Waitrose publish specifically for lamb, so we haven’t built a precise adjustment into this timer. If you do stuff the joint, check the centre of the stuffing itself reaches a safe temperature, not just the meat around it — and note that stuffing effectively turns the leg into a rolled joint, so it should be cooked through rather than served pink.
Sources: Food Standards Agency — Cooking your food (the whole-cuts rule and the rolled-joint exception); Waitrose — Roast Lamb Cooking Times & Tips. This page is general cookery guidance, not a substitute for the instructions on your joint’s packaging.