We are cooking a home raised bird this year, he is 28.5 pounds, he will be unstuffed. We have a good meat thermometer, so the bird will come out of the oven when we get 150°F, or 155°F, and rest for 20 ~ 30 minutes on the counter to reach 165°F.

How long should we plan on cooking it, and at what temperature?
Thanks,

Roughly 5 hours at 325 degrees.
I bought 2 a 16 and 20 pounder for my wife and I.We love turkey and will start with the 20 pounder.And thats for later as we will be eating turkey at one of the kids home.
Tom

Thanks,

About 15 to 20 mins a lb unstuffed

For a 28.5 lb turkey? I don't think so! 7-8 hours.

Just cooked a 37 pounder last Saturday for our church dinner. Also unstuffed, 2 hours at 325 and 2 hours at 350. Key to a great tasting, moist bird is to cook it then place it in a container with a top so it can steam for at least 1 hour. Bigger birds like your 28 pounder I line a cooler with aluminum foil, place the bird in the cooler, close the lid. Also a great way to transport turkey if you are cooking it at a location not near where you are eating it.
I always brine my turkeys for 36 to 48 hours before cooking.
Simple brine is 1/2 gallon apple cider, 1 1/2 cups Kosher salt, 2 cups brown sugar, 1 tablespoon black pepper, 3 oranges sliced with peel left on, 1 garlic minced, 1 gallon water.
Bring to hard boil, let cool to room temperature. Add one gallon of ice and the turkey. Rotate turkey every few hours. Again I use a cooler to brine them in.
NOTE: this brine also works fantastic for venison!!

Google it.If I could post a link I would. USDA how long to cook a turkey.Gives exact times for stuffed or unstuffed turkeys.

I forgot to mention: Do not brine a store bought turkey without reading the label on the turkey first. Most store bought turkeys are injected with sodium and brineing them will over load 'em with salt.

Yote got it right and no opening the oven before hand
We always had one that big for the family get-togethers with the 40+ cousins. Make sure there is plenty of party-stuffers for a late cooking turkey with big crowds like that.

Also to add, once your turkey is done, if you wrap it in foil and put it in a cooler it will stay warm for hours. Better to start early and keep it warm than have a crowd waiting and a half raw turkey.