How to choose the size of a kotatsu futon
Ideally, a kotatsu futon should be about 43" to 51" (110 to 130 cm) larger in both length and width than the kotatsu tabletop.
This means that the futon will be at least 21" (55 cm) larger than all four sides of the table.
However, these days, kotatsu tables tend to be taller. The average height of a kotatsu is said to be about 15" (39 cm). If your kotatsu is taller than this, a larger futon may be more suitable.
It is recommended that you choose a cover for your kotatsu futon that is the same or about 2″ / 5 cm larger than the kotatsu futon.
About the size of the kotatsu mat
If you are not sure about the size of your kotatsu mattress (kotatsu rug), use "the width of the kotatsu top + 39 inch (100 cm)" as a guide.
For example, if your kotatsu table is 31.5 inch (80 cm) wide, the size of the kotatsu mattress should be 31.5 + 39 = 70.5 inch ( 80 cm + 100 cm = 180 cm) or more.
This will give you 20 inch (50 cm) of space to sit on each side of the tabletop.
Tatami mats are also ideal as a kotatsu mat. How about creating a wonderful “Japanese-style corner” in your room?