Why kitchens are priced by the metre
A kitchen is a row of boxes with doors on. What you are buying is the length of that row, not the size of the room it sits in.
So a quote is built from the run: so many metres of base units, so many of wall units, so many of worktop.
This is why a large open plan kitchen with a modest run of units can cost less than a small galley kitchen packed with cabinets on both walls.
It also means the first thing to do before getting quotes is to measure the run you actually want. Walk the layout and add up the lengths.
Tall units, larders and island units are usually priced separately again, because they are more material and more work than a standard base unit.
