Back in the days before standards for blankets existed & the only testing done (if any) was of the material to BS475 you could have any size.
Usually the smallest was 3' x 3' (90cm x 90cm), although the odd 80 x 90cm would slip through (First Alerts was of this size). Sizes were usually 3'x3', 3'x4', 4'x4', 4'x6', 6'x6' (& their metric equivalents)
BS 6575 brought in tests and specifications, which were transferred over to the current BS EN 1869. The minimum size of any side is 90cm, the maximum 180cm.
In general the 90cm and 110cm sizes have virtually disappeared from sale and the most common sizes are 1m x 1m, 1.2m x 1.2m and 1.2m x 1.8m.
The size bit is being picky for picky's sake, particularly as I bet most of those kitchens don't need any blanket. They are designed for and tested only on small Class F fires in pans up to 345mm dia./3 litres capacity, with a supplementary usage on fires in clothing.
If your kitchen doesn't use cooking oil pans or naked flame hobs you do not need a fire blanket period. You may require CO2 for electrically energised equipment such as microwaves. "kitchens" & fire blankets is one of those urban myths dating back to prescription & FOC Rules, where you would have had to put in every area defined as a kitchen (& admittedly in those days most would have had hobs and pans) two 2 gallon chemical foam extinguishers and an asbestos blanket regardless of size or use.
The reason you still see them is because the myth is perpetuated by assessors who don't know any better & extinguisher companies who wish to flog kit.