If you are in the UK use this site for a guide: http://www.britishturkey.co.uk/cooking/times.shtml

Epicurious has a great chart for turkey doneness, taking into account turkey size, oven temp & time: http://bit.ly/dMQo7M But it's best to take the internal temperature too -- you'll want to hit at least 150 in the fleshy part of the thigh (the temp will continue to climb as it rests).

http://www.butterball.com/tips-how-tos/how-tos/know-when-your-turkey-is-done