I bought mine from a flooring store. It's 3/8" thick and is very similar to broadloom carpet padding. This type of padding is commonly used by my decorator.

We have just bought more padding from a different store without our decorator for a new area rug last week. The store had to special order it for us. Some stores that work with decorators may have it in stock. We took 3 inches off the total width and 3 inches off the total length. That means there is an 1 1/2" difference total all around. It's perfect.

With this in mind, my recommendation would be 5x8 for your rug. This will allow the edges for lay flat.

Jerseygirl, you would recommend a 5 by 8 pad for an 8 by 11 rug?? I am confused because you mentioned taking 3 inches off the length and width but then 5 by 8 is more like 3 feet off the length and width . ..

Thanks for the reply!

I second jerseygirl's advice. We just purchased a thick rug pad on Friday for our new DR rug. I got it from a local rug store where we purchased the area rug. They cut it to size for me. The pad was about $80. My rug is roughly 8x10 and they cut the pad 3" shorter than the width and length - 7'9" x 9'9". The off-the-shelf rug pad was a little cheaper at $60 but I wanted a pad that wouldn't slip and would offer the best protection for the rug and floor. The store manager recommended the one we purchased.

I ordered mine online. It works great. Have no problems with it.

Here is a link that might be useful: Rug Pad

When we bought our Persian rugs they cut a thick pad to size for it. It just fits under the rug. In fact, a few times it has stuck out and we have just kind of cut a slice off so it doesn't show. But if you get a thick pad and you try to put a 5x8 pad under an 8x11 rug, you will clearly be able to see where the pad ends from looking at the rug and the rug will be flat in the unpadded areas. The pad should be cut so that it just fits under the rug. I don't think you want a large border of unpadded rug showing, it won't look good.

Sorry, What was I thinking! 7.9 X 10.9.

jerseygirl,sorry to keep on bothering you but do you know the brand, name, even the name of the flooring store you got your pad from. The thickest I can find online or here in Chicago is 3/16 in. thick and I would love a thicker pad of 3/8 since our baby just started crawling.

Thanks everyone!!

CDS
I don't know the brand. We ordered the last set of area rugs from a flooring place in Philadelphia. He had to special order it for us. I will have to look at the receipt when my DBF gets home from work. Maybe there is a name on it.

I went to a discount carpet barn and had them cut 3 5x8
pads for my 3 rugs out of regular thick carpet pad they lay carpet over.

My rugs feel and look so plush under foot now.
I had to trim them down some for 5x8 area rugs.
They don't slide, rugs don't slide and the total price for 3 pads was on sale.....$27..plus tax. For all 3.

Just an el-cheapo at Walmart was $30 something for one.
No thickness.

I have a couple extra thick pads (I think they call them rug cushions) from the site www.addarug.com. They are not cheap, but are the thickest (1/4") I could find and really luxurious. Free shipping, too.

What kind of pad should you use on prefinished hardwood floor, under Oriental (wool) carpet? I don't want anything with latex that might stick to the finish with heat/humidity/weight of table. Thanks