How Long to Cook Leg of Lamb: Perfect Timing Guide

A leg of lamb (5-7 lbs) requires 15-20 minutes per pound at 325°F (163°C) to reach medium-rare (145°F internal temperature), followed by a 15-20 minute rest period for optimal juiciness and tenderness.

Nothing elevates a special occasion meal like a perfectly cooked leg of lamb. Get the timing right, and you'll achieve succulent, flavorful meat that falls off the bone. Get it wrong, and you risk dry, tough results that disappoint your guests. This guide delivers precise cooking times based on weight, oven temperature, and desired doneness—plus professional techniques to ensure success every time.

Why Precise Timing Matters for Leg of Lamb

Lamb's delicate flavor and texture demand careful attention during cooking. Unlike poultry or pork, lamb benefits from slightly higher internal temperatures while maintaining tenderness. Undercooking leaves an unpleasant gamey taste, while overcooking transforms tender meat into dry, stringy fibers. The sweet spot lies in understanding how weight, starting temperature, and oven conditions interact.

Essential Preparation Steps Before Cooking

Proper preparation sets the stage for perfect results:

• Bring lamb to room temperature (remove from refrigerator 1-2 hours before cooking)
• Pat dry with paper towels for optimal browning
• Score fat cap in diamond pattern to render fat evenly
• Season generously with salt, pepper, and aromatic herbs
• Preheat oven to ensure consistent cooking from the start

Leg of Lamb Cooking Time Guide

These guidelines apply to bone-in legs (5-7 lbs) roasted at 325°F (163°C). Always use an instant-read thermometer for accuracy:

Weight	Medium-Rare (145°F)	Medium (160°F)	Well-Done (170°F)
5 lbs	75-100 minutes	100-125 minutes	125-150 minutes
6 lbs	90-120 minutes	120-150 minutes	150-180 minutes
7 lbs	105-140 minutes	140-175 minutes	175-210 minutes

Note: Boneless legs cook approximately 20% faster than bone-in. Always verify with a thermometer rather than relying solely on time.

Temperature Guide for Perfect Doneness

The USDA Food Safety and Inspection Service recommends minimum internal temperatures for lamb safety, but culinary professionals often adjust based on preference:

• Rare: 125-130°F (final 130-135°F after resting) - very red center
• Medium-Rare: 135-140°F (final 145°F) - warm red center (recommended for best texture)
• Medium: 145-150°F (final 160°F) - pink center
• Well-Done: 160°F+ (final 170°F+) - little to no pink

Remember that carryover cooking will raise the internal temperature 5-10°F during resting. Remove lamb from oven when thermometer reads 5°F below your target temperature.

Step-by-Step Cooking Process

Follow these professional steps for restaurant-quality results at home:

1. Preheat oven to 325°F (163°C) - avoid higher temperatures that cause uneven cooking
2. Place lamb fat-side up on a rack in a roasting pan
3. Insert oven-safe thermometer into thickest part (avoiding bone)
4. Roast undisturbed until thermometer approaches target temperature
5. Baste with pan juices every 30 minutes for added flavor (optional)
6. Check temperature 20 minutes before expected finish time
7. Remove when 5°F below target temperature (carryover cooking will finish the process)

The Critical Resting Period

Resting isn't optional—it's essential for juicy results. During cooking, meat fibers contract and push juices toward the center. Resting allows these juices to redistribute throughout the meat.

For a leg of lamb:

• Cover loosely with foil to retain heat
• Rest for 15-20 minutes (1 minute per pound is a good rule)
• Do not skip this step—cutting too soon releases precious juices
• Internal temperature will continue rising 5-10°F during rest

Troubleshooting Common Issues

Even experienced cooks encounter challenges. Here's how to handle them:

Problem: Uneven Cooking

Solution: Rotate pan halfway through cooking. For significant temperature variations in your oven, position the thicker part of the leg toward the back where heat is usually more intense.

Problem: Excessive Smoke or Burning

Solution: Add 1 cup of water to the bottom of the roasting pan. This creates steam that prevents drippings from burning while maintaining oven humidity.

Problem: Meat Too Dry

Solution: Next time, reduce cooking time by 10-15% and rely more on thermometer readings than clock time. Consider brining the lamb for 12-24 hours before cooking to improve moisture retention.

Special Considerations for Different Cooking Methods

While conventional oven roasting is most common, these adjustments apply to alternative methods:

• Grilling: Use indirect heat at 325°F. Cooking time similar to oven but requires more frequent temperature checks
• Sous Vide: Cook at 130°F for 24-48 hours, then sear for crust (requires precision equipment)
• Slow Roasting: Cook at 275°F for 4-5 hours for ultra-tender results (ideal for larger legs)

Modern convection ovens reduce cooking time by approximately 25%—adjust accordingly and monitor temperature closely.

Serving Your Perfectly Cooked Leg of Lamb

After resting, carve against the grain for maximum tenderness. For presentation:

• Remove the aitch bone for easier carving
• Slice ¼-inch thick against the grain
• Serve with pan juices or a complementary sauce
• Pair with roasted vegetables, mint jelly, or a red wine reduction

Leftovers make excellent cold cuts for sandwiches or can be repurposed into shepherd's pie, lamb curry, or salads.

Frequently Asked Questions

How long should I cook a 6 lb leg of lamb at 325°F for medium-rare?

A 6 lb leg of lamb requires approximately 90-120 minutes at 325°F to reach medium-rare (145°F internal temperature). Always verify with a meat thermometer rather than relying solely on time, as oven temperatures can vary. Remove the lamb from the oven when the thermometer reads 140°F, then let it rest for 15-20 minutes before serving.

Should I cover leg of lamb while roasting?

No, you should not cover a leg of lamb while roasting. Keeping it uncovered allows the fat to render properly and creates a beautiful crust on the exterior. Covering traps steam which prevents proper browning and can make the meat texture less appealing. Only cover with foil during the resting period after cooking.

Why does my leg of lamb always turn out dry?

Dry leg of lamb typically results from overcooking or skipping the resting period. Lamb continues to cook from residual heat after removal from the oven (carryover cooking), so remove it when thermometer reads 5°F below your target temperature. Additionally, insufficient resting time prevents juices from redistributing. Always rest for 15-20 minutes before carving. For future reference, consider using a meat thermometer rather than relying solely on cooking time.

Can I cook leg of lamb from frozen?

While possible, cooking leg of lamb from frozen is not recommended. It significantly increases cooking time (approximately 50% longer) and leads to uneven results with potentially overcooked exterior and undercooked interior. For best results, thaw the lamb in the refrigerator for 24-48 hours before cooking. If you must cook from frozen, increase cooking time by 50% and use a thermometer to verify internal temperature, as time-based estimates become unreliable.