What size cutting mat should i start with? I'm very new to quilting and just trying to get some basic gear together to try a beginners quilt. 12X9 12X18 18X24 or 24X36?

Personally I prefer the 18x24 or the 24x36. You have to take into consideration what size your work space is, whether or not you need to store it, storage space, etc.
I also like an even smaller one or the 12x12 turning one to take to classes. They're about the same as rulers, bigger ones are great but so are the smaller ones depending on where you're using them and the size of what you're working with.
As long as it's big enough to do what you want and small enough not to be clumsy you should be fine.

I am also a new quilter and I started off with a Fiskers' beginning quiting set I got from Joann's Fabrics.

It has an 18 x 24" cutting mat, a 6 1/2 x 24" ruler, and a 45mm rotary cutter.

If you buy the set when they have the 40-50% off coupons, you will only pay between $25 and $30.00 for the whole set.
I have never had any reason to use a larger mat, but have only been quilting for a few months. For the price it is a good start.

I just checked online, the regular price is $47.99.

im thinking that i wont be making blocks bigger than 12" so maybe i can get by with 18X24?

Joe,
Remember its not so much the size block as the size of the fabric to be cut. I find it much easier to layout my fabric on the larger mats so I can strip cut. I don't like to cut through more than 2-4 layers at once, as a waviness can occur in your strips. My board, I believe, is 24 x36. I do have smaller ones that I used when I belonged to a guild, once I already strip cut the fabric though.

Does this make sense?

Your actual blocks may not be over 12 inches, but don't forget that you'll need to cut bindings also. Raptureready is right though, it depends on how much room you have and how much you can afford. Personally speaking I would go for the largest one.

I love my big 36x24 mat! :D

thanks you've all given me a lot to think about

alway get the biggest mat you can afford. i bought a small when when i first started, woo, what a pain. Used a 50% coupon at Joan or hancocks and got the 36 inch one. What a difference.

But remember, we can all make do with a little less if it is all we can afford. There are no rules, just new experiences. :)

18 X 24 would be my minimum... I have a 12 X 24 that is getting replaced this summer, it is BARELY big enough to square up a 12 in block.... you may not think you will make this size blocks now, but in the future there may be a pattern that really grabs your attention :wink: If you have the room and can afford it, bigger is better in this case :D:D:D