Oak door casing

[stevegreen]

Hi, i'm wanting to fit a door casing (in readyness for plastering), but havent bought the door yet. The opening is for 2'9" door approx , what internal measurements should a finish the casing to give me the right amount of clearance for the future door.
Thanks

 

[joinerjohn]

Whatever size the door is + 1/4" probably. Either that or set the door casing at 2'9" then you'll have to work on the door to fit it.
Don't forget to add about half an inch to the height if you have carpets etc
And, don't forget to protect the casing, Oak and water (off the plastering) is a recipe for disaster.