I've measured for a upvc door, opening is 2025x930mm, do I get door that is 2025x930 or slightly smaller?

smaller ..the frame is at least 50mm either side ..and you have a head similar as well as cill ...so your door is slightly wider than average ..but its also shorter ...standard height for upvc frame is 2100 ...so your door will be about 6ft 3" ..3" short of standard

If your measurements are brickwork to brickwork (what is called ' tight' dimensions) then allow 6mm in the height and width for clearance purposes (3mm all round). so = 2019 x 924. This will enable the door and outer frame to fit in snuggly and when you fix the frame to the brickwork you use 2 or 3mm plastic packers near your fixings to take up the slack, the gap that is left is usually then covered using a white or coloured silicone.