If you’re planning a big holiday meal or special gathering, knowing how long to cook 20 lb ham in oven is essential. Getting the timing right ensures a perfectly cooked centerpiece that’s juicy, flavorful, and safe to eat.
A large ham can feel intimidating, but the process is straightforward. We’ll walk you through every step, from preparation to carving. You’ll learn the exact temperatures, timing, and techniques needed for success.
This guide covers both fully cooked and fresh hams. The cooking method differs for each, so it’s important to know what you have. Let’s get your ham ready for the oven.
How Long To Cook 20 Lb Ham In Oven
The total time for a 20 lb ham depends on its type. A fully cooked, bone-in ham needs about 15-18 minutes per pound at 325°F. This means roughly 5 to 6 hours of total oven time. A fresh (uncooked) ham requires longer, about 22-26 minutes per pound, totaling 7 to 9 hours.
Always use a meat thermometer to check for doneness. This is the only reliable way to know your ham is perfectly cooked. We’ll cover the target temperatures next.
Understanding Your Ham: Fully Cooked vs. Fresh
Before you preheat the oven, check your ham’s label. This is the most important step.
- Fully Cooked or “Cook Before Eating” Ham: Most hams sold in the US are cured and fully cooked during processing. They are safe to eat without further cooking, but heating improves flavor and texture. The label might say “Fully Cooked” or “Cook Before Eating.”
- Fresh Ham: This is essentially a raw pork leg. It has not been cured or smoked. It requires thorough cooking to a safe internal temperature, similar to a pork roast. The label will say “Fresh Pork Leg” or “Fresh Ham.”
Mistaking one for the other will lead to major timing errors. If you’ve lost the packaging, a fully cooked ham is usually pink from curing, while a fresh ham looks like raw pork.
Essential Tools and Ingredients
Gather these items before you start. It makes the process smooth.
- A large roasting pan with a rack
- Meat thermometer (instant-read or leave-in probe type)
- Aluminum foil
- Sharp knife for scoring
- Basting brush
- For the ham: Brown sugar, mustard, honey, cloves, pineapple juice, or your prefered glaze ingredients.
Choosing Your Roasting Pan
A 20 lb ham is big. Ensure your roasting pan is large enough to hold it with some space on the sides. Using a rack lifts the ham, allowing heat to circulate evenly. If you don’t have a rack, you can create a bed of sturdy vegetables like onions or carrots to lift it slightly.
Step-by-Step: Cooking a Fully Cooked 20 lb Ham
This is the most common scenario. Follow these steps for a juicy, flavorful result.
1. Preparation and Preheating
Take the ham out of the refrigerator about 1-2 hours before cooking. Letting it come closer to room temperature promotes even heating. Preheat your oven to 325°F (165°C). Adjust the oven racks to fit the large pan.
Remove any packaging and netting. Place the ham, flat side down, on the rack in the roasting pan. If the ham has skin, you can trim some of the excess fat, leaving about a 1/4-inch layer.
2. Scoring and Adding Moisture
Using a sharp knife, score the surface fat in a diamond pattern. Make cuts about 1/4-inch deep. This allows the glaze to penetrate and gives the ham a nice appearance.
Add about 1-2 cups of liquid to the bottom of the pan. Water, apple juice, or broth works well. This creates steam and prevents the drippings from burning. Cover the ham tightly with aluminum foil. This initial covered cooking stage keeps it moist.
3. Initial Baking Time
Place the covered ham in the preheated oven. For a 20 lb fully cooked ham, plan for about 12-15 minutes per pound for this first stage. That’s about 4 to 5 hours. The foil trap the heat and steam, gently warming the ham throughout.
4. Glazing and Final Baking
About 45 minutes to an hour before the total time is up, remove the ham from the oven. Carefully take off the foil—watch for steam. Increase the oven temperature to 375°F (190°C).
Apply your glaze generously over the scored surface. Return the ham to the oven, uncovered, for this final period. The higher heat will caramelize the glaze and create a beautiful crust. Baste with pan juices every 15 minutes.
5. Checking for Doneness
The ham is ready when an instant-read thermometer inserted into the thickest part (not touching bone) reads 140°F (60°C). Remember, it’s already fully cooked, so you are just heating it to the ideal serving temperature.
Once it reaches 140°F, remove it from the oven. Tent it loosely with foil and let it rest for 20-30 minutes before carving. Resting allows the juices to redistribute, making every slice tender.
Step-by-Step: Cooking a Fresh 20 lb Ham
A fresh ham is a different project, requiring longer cooking to a higher temperature.
1. Preparation is Key
Preheat the oven to 325°F (165°C). Pat the fresh ham dry with paper towels. Season generously with salt, pepper, and any herbs you like. You can also inject it with a marinade for extra flavor.
Place it on a rack in a roasting pan, fat side up. Scoring the skin and fat is highly recommended for a fresh ham to help render the fat and crisp the skin.
2. Roasting Time and Temperature
Do not cover a fresh ham. It needs dry heat to roast properly. Place it in the oven and plan for 22-26 minutes per pound. For a 20 lb fresh ham, this is approximately 7 hours and 20 minutes to 8 hours and 40 minutes.
Start checking the internal temperature after about 6 hours. Add liquid to the pan if the drippings start to burn.
3. The Crucial Internal Temperature
A fresh ham must be cooked to a safe internal temperature. The USDA recommends 145°F (63°C) for pork, followed by a rest time. Insert the thermometer into the center of the thickest part.
When it hits 145°F, take it out. The temperature will rise a few degrees during resting. Cover it with foil and let it rest for a full 30 minutes. This rest is non-negotiable for a juicy roast.
Creating and Applying the Perfect Glaze
A glaze adds flavor and a gorgeous finish. Apply it only in the last 45-60 minutes of cooking to prevent burning.
Here’s a simple, classic glaze recipe:
- 1 cup brown sugar
- 1/2 cup honey or maple syrup
- 1/4 cup Dijon mustard
- 2 tablespoons apple cider vinegar
Mix all ingredients in a saucepan over medium heat until smooth. Let it cool slightly before brushing it on. For extra flavor, stud the scored diamonds with whole cloves before glazing.
Carving Your 20 lb Ham Like a Pro
After resting, it’s time to carve. Use a long, sharp slicing knife.
- Place the ham on a stable cutting board, flat side down.
- If there is a bone, locate it. For a shank ham (pointed end), make vertical slices down to the bone, then cut along the bone to release the slices.
- For a butt half (more rectangular), the bone is shaped differently. Slice parallel to the bone, then turn the ham to remove slices from other sides.
- Cut slices about 1/4 to 1/2-inch thick.
Common Mistakes to Avoid
- Not Using a Thermometer: Guessing leads to dry or undercooked ham. Always use a thermometer.
- Overcooking a Fully Cooked Ham: Heating it beyond 140°F will dry it out. It’s already safe to eat.
- Adding Glaze Too Early: Sugar burns quickly. Apply only at the end.
- Skipping the Rest: Carving immediately lets all the juices run out onto the board.
- Using a Too-Hot Oven: Low and slow (325°F) is the rule for even cooking without drying.
Storing and Reheating Leftovers
Leftover ham is a treasure. Store it properly.
Wrap sliced ham tightly in plastic wrap or foil, or place in airtight containers. Refrigerate for up to 5 days. For longer storage, freeze for up to 2 months. To reheat, place slices in a baking dish with a splash of broth or water, cover with foil, and warm in a 325°F oven until heated through.
The bone is perfect for making soup or beans. Just store it in the freezer until your ready to use it.
Frequently Asked Questions (FAQ)
How long does it take to cook a 20 pound ham at 325 degrees?
For a fully cooked ham, about 5 to 6 hours total. For a fresh ham, plan for 7 to 9 hours. Always use a meat thermometer to be sure.
Should I cover a ham while baking?
Yes, for a fully cooked ham, cover it tightly with foil for most of the cooking time. Remove the foil for the last hour to apply glaze. For a fresh ham, do not cover it.
What temperature should a 20 lb ham be cooked to?
A fully cooked ham needs to reach an internal temperature of 140°F. A fresh ham must be cooked to at least 145°F, followed by a rest period.
How do I keep my ham from drying out?
Using a roasting pan with liquid, covering a fully cooked ham for the initial phase, and not overcooking it are key. Letting it rest before carving also keeps it juicy.
Can I cook a ham overnight on low?
It’s not recommended for a ham this size in a conventional oven due to food safety concerns. The prolonged time in the “danger zone” (40-140°F) could allow bacteria to grow. It’s safer to cook it day-of.
What’s the best way to reheat a whole cooked ham?
Reheat it the same way you cooked it: in a 325°F oven, covered, with liquid in the pan. Heat until it reaches 140°F internally. This may take a couple hours for the whole ham.
Final Tips for Success
Planning is your best friend when cooking a large ham. Calculate your start time based on the 15-18 or 22-26 minutes per pound guide, plus resting time. Remember, a rested ham is a better ham.
Don’t be afraid of the size. A 20 lb ham feeds a crowd and creates wonderful leftovers. With a good thermometer and this guide, you’ll have a delicious centerpiece for your celebration. The process is simple when you take it step by step.