I am sorry if this is a stupid question, but what is the standard card size? Is it the same size as magic cards?

It´s not a stupid question - i purchased the wrong card sleeves today.

Standardsize is magic size. So LOTR card sleeves size = Magic = Game of thrones = Cuthulu.

I've just been looking myself, since the cards will definitely need protection.

The cards in the following link should be the right ones - you get 50 for $2.99 and they are sized 2 1/2" x 3 1/2" (63.5 x 88 MM), not bad at all -

2 1/2" x 3 1/2" (63.5 x 88 MM) Card Game Sleeves (solid coloured)

I'll probably get the White Card Game Sleeves myself.

There will be art sleeves made for the LOTR CG too, but are currently unreleased. They have packs with the following images - Nazgul, Golden Wood Singer, Gandalf, Gimli, The One Ring and Eye of Sauron. Those are a bit dearer at $4.99 for a pack of 50. I'll probably get a few of these packs too at some point.

Thanks for the links. I think I want the clear sleeves myself, because I love the art on back. Even though my Gandalf cards are marked (each one has a horizontal line going through both front and back) I promise to try to play fairly if I use the clear sleeves.