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?

Lamb is traditionally served pink (medium) in the UK and is perfectly safe to eat this way, unlike pork and chicken. Medium (63°C internal) gives juicy, flavourful meat with a pink centre. Well done (72°C) is also popular and is the preference in many cultures. Rare lamb (54°C) is less common but favoured by some chefs for tender cuts like rack.

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.

BakeCalcs

Lamb Joint Calculator

Calculate cooking time for lamb joints based on weight and preferred doneness.

Joint Weight

Doneness

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.

Frequently Asked Questions

Related Calculators

Roasting Time Calculator

Calculate roasting time for beef, lamb, pork, chicken, and turkey by weight and doneness.

Turkey Roasting Calculator

Calculate cooking time, temperature, and resting time for turkey based on weight.

Chicken Roasting Calculator

Calculate roasting time and temperature for whole chicken by weight.

Beef Joint Calculator

Calculate cooking time for beef joints based on weight and preferred doneness.

Pork Joint Calculator

Calculate cooking time for pork joints based on weight.

Last updated: February 2026

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