http://www.fsis.usda.gov/Fact_Sheets/Lets_Talk_Turkey/index.asp
Thawing Your Turkey
There are three ways to thaw your turkey safely — in the refrigerator, in cold water, or in the microwave oven.
In the Refrigerator (40 °F or below)
Allow approximately 24 hours for every 4 to 5 pounds
4 to 12 pounds 1 to 3 days
12 to 16 pounds 3 to 4 days
16 to 20 pounds 4 to 5 days
20 to 24 pounds 5 to 6 days
Keep the turkey in its original wrapper. Place it on a tray or in a pan to catch any juices that may leak. A thawed turkey can remain in the refrigerator for 1 to 2 days. If necessary, a turkey that has been properly thawed in the refrigerator may be refrozen.
In Cold Water
Allow approximately 30 minutes per pound
4 to 12 pounds 2 to 6 hours
12 to 16 pounds 6 to 8 hours
16 to 20 pounds 8 to 10 hours
20 to 24 pounds 10 to 12 hours
Wrap your turkey securely, making sure the water is not able to leak through the wrapping. Submerge your wrapped turkey in cold tap water. Change the water every 30 minutes. Cook the turkey immediately after it is thawed. Do not refreeze.
In the Microwave Oven
Check your owner's manual for the size turkey that will fit in your microwave oven, the minutes per pound, and power level to use for thawing.
Remove all outside wrapping.
Place on a microwave-safe dish to catch any juices that may leak.
Cook your turkey immediately. Do not refreeze or refrigerate your turkey after thawing in the microwave oven.
REMINDER: Remove the giblets from the turkey cavities after thawing. Cook separately.