Firstly the size in terms of pricing is defined more by the number of cabinets and whether the design is simple or elaborate, than the actual room size but obviously the larger the room the more it’s going to cost. If you aren’t sure then the answer is probably ‘somewhere in between’
SMALL
Up to about 8 sq.m. Perhaps a galley kitchen in a terraced house or an L-shape with a limited number of cabinets. Small kitchens often have proportionally fewer cabinets and more appliances.
MEDIUM
Up to 18 sq.m. A typical modern house maybe with room for a small breakfast bar of table. Room for a range cooker.
LARGE
Over 18 sq.m. Definitely room for an Island and possibly a table too. An Americal fridge and an AGA won't be out of place. Could also cover a medium kitchen with a utility room.