I have about 5 or 6 - different sizes.

24x36
13x13

Yikes!!! I only have one!

I have 10 in various sizes; a couple that rotate; a couple I only take to classes; small one for little stuff and 4 big ones. My favorite of the big is the Martelli. My least favorite is an outrageously priced Ginhger that immediately got groves and curls of the mat on top. What a waste of money.

Too many to count. I have lots. Most were bought on clearance and are now triple in price to buy today. I love the Martelli mat and the colors of the June Taylor. I have mostly Olfa brand in the big mats. The Polar mats are nice if you can find them now. I have three rotating mats, one which is 18 x 24, I use that the most. Use to Hancock Fabrics had 50% off sales on everything quilting, scissors, mats, rulers, anything. I would by by the cart full at those sales. I'm so glad I did.

I have three:
24" X 36" which I mostly use for cutting backing, batting, and border fabrics-- long yardage--
18" X 24" which I use a lot, and
12" X 18" which stays right next to my sewing machine. I use it for trimming and squaring up. It also fits nicely in my travel tote for classes, workshops, and quilt camp.

three

3...one large green one, 1 small green one...and just for fun, I had to have a purple one for my room!

two 24x36
two rotating cutting mats, one small , one large
two small cutting mats

2 rotating, 1 with ironing board on back, 1 large, 1 medium; they are in NY and I'm in FL so can't measure.