What is the formula for roasting lamb?

For lamb at 180°C fan: Medium is 25 minutes per 500g plus 25 minutes. Well done is 30 minutes per 500g plus 30 minutes. Pink (rare) lamb is 20 minutes per 500g plus 20 minutes. A 1.5kg leg of lamb at medium takes about (1500/500 x 25) + 25 = 100 minutes. Use a meat thermometer to confirm doneness.

Which cuts of lamb are best for roasting?

The leg is the most popular roasting cut — it has good flavour and feeds a crowd. Shoulder is fattier and more flavourful, excellent for slow roasting until it falls apart. Rack of lamb (French-trimmed) is elegant but smaller and cooks quickly. Half-leg or mini roast joints are perfect for smaller households. Bone-in joints generally have more flavour than boneless.

Should lamb be served pink?

A whole lamb joint (intact muscle such as a leg, shoulder or rack) is traditionally served pink in the UK and is safe this way, unlike minced lamb, pork or chicken which must reach 75°C. The Food Standards Agency advises a minimum core of 63°C for whole lamb joints. Medium (63°C internal) gives juicy, flavourful meat with a pink centre; well done (71°C) is also popular. Rare lamb (52°C) is less common but favoured by some chefs for tender cuts like rack. Always check the centre of the thickest part with a meat thermometer rather than relying on time alone. Minced lamb, burgers and sausages must be cooked right through to 75°C.

Should I add garlic and rosemary to lamb?

Garlic and rosemary are the classic accompaniments to roast lamb. Make small incisions in the meat with a sharp knife and push in slivers of garlic and small sprigs of rosemary before roasting. Anchovies pushed into the incisions also work beautifully — they melt into the meat during cooking and add umami depth without a fishy taste.

How do I get crispy lamb skin?

Score the fat in a criss-cross pattern, rub with oil and salt, and start the oven at 220°C for the first 20 minutes before reducing to 180°C. The high initial heat renders the fat and crisps the skin. For shoulder, slow-roasting at 160°C for several hours also produces excellent crispy skin as the fat renders gradually over a longer period.

Lamb Joint Calculator — Free Online Tool

How We Calculate This

This calculator uses the standard UK lamb roasting formula at 180°C fan. Medium is 25 minutes per 500g plus 25 minutes, well done is 30 minutes per 500g plus 30 minutes, and rare is 20 minutes per 500g plus 20 minutes.

Resting time is calculated at 1 minute per 100g, with a minimum of 15 minutes and maximum of 30 minutes. Serving estimates are based on approximately 300g of raw bone-in lamb per person.

Food safety: these times are a starting guide only — ovens and joints vary. Always confirm doneness with a meat thermometer in the centre of the thickest part. A whole lamb joint may safely be served pink at a 63°C core (Food Standards Agency minimum), but minced lamb, burgers and sausages must reach 75°C. Target core temperatures here (rare 52°C, medium 63°C, well done 71°C) are the reading after resting; remove the joint a few degrees early as the temperature keeps rising while it rests.

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Last updated: February 2026

All calculations are based on standard ratios and conversions. Results may vary with specific ingredients, equipment, and conditions.