Door frame standard internal width for a 686mm door

[jacoscar]

I need to build a door frame for a 686mm door. The reason I’m doing it is because I want a transom window and I’ve made the wall thicker by adding tile backer boards.
I’ve measured the door and it’s actually 684mm wide instead of 686, the door is new.
Is 686mm the width of the frame or some kind of nominal measure? What should be the internal width of a frame? I want to be able to change the door in the future without trimming it

 

[Diver Fred]

That's a 27 inch door.
When we worked completely in Imperial measurements we would allow 1/8inch either side of the door for the door reveal,

Nowadays the clearance seems to be settling on 2mm but with some relief on the lock side to prevent binding.

May suggest that you visit one of the DIY big barns and measure up a 27inch door lining for the width that finishes.

 

[jacoscar]

That's a 27 inch door.
When we worked completely in Imperial measurements we would allow 1/8inch either side of the door for the door reveal,

Nowadays the clearance seems to be settling on 2mm but with some relief on the lock side to prevent binding.

May suggest that you visit one of the DIY big barns and measure up a 27inch door lining for the width that finishes.

Hello, I checked out and measured door frames in Wickes and I found two different answers:

MDF door frame: 691mm for a 686 door
Softwood door frame: 688mm for a 686 door

The softwood seems tight with only 1mm clearance per side, unless they swell when painted?