MOR gave you a good answer concerning "Fly" plaids. Usually 40" x 40", Though the better ones will go 50"x50". It is the evolution of the day/piper/Laird plaid, which is evolution of the top half of a great kilt.
The day/piper/Laird plaid is 48" to 54" (double width) wide and can go 6' to 9' in length. The most popular commercially made is 48"x 8' and is marketed as a piper plaid. (See SWK's accessories) As, one of the names implies, it is suitible for day wear. There have been many lengthy threads on how to wear this. Use the search engine with of one these key words.
Hopefully, I have given you a quick answer, to start you in direction for more info. I'm sure others will elaborate as well.
Here is a pic of me with what I would call a day plaid. It is actually comercially made and sold by SWK.
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