Simplify the following text for a Grade 4 native English-speaking person.
Original: They were knitted and became thicker like modern tatami . People who lived in the Heian Era stepped onto tatami to show their power and they spread the tatami only in a necessary part of the room .
Simplified: In the Kyoto area , tatami generally measure .955 m by 1.91 m. Tatami of this size are referred to as KyÅ ma tatami .