How to Buy - Measuring Measure the opening with of the door frame where the door sits, be sure to take three measures an the top bottom and middle of the door frame and note the widest dimension. Measure the height of the door frame again where the door sits, be sure to measure each side ans again not the highest dimension.
If door stops are fitted then also make a note of the dimension from the edge of the door frame to the door stops.
Choose a door that will suit the dimensions you have. Timber doors can typically be cut down by as much as 12mm per edge and so an oversize door can trimmed down to fit. (Check the specifications of your chosen door for the maximum that can be removed).