When ordering window curtains, am I ordering one curtain for my whole window, or one for each side?

Question

I want to buy new curtains for my bedroom. Do I have to buy one curtain for the left side of my window and one for the right side of my window? Or when I order them online, do I just buy one curtain for the whole window? I am talking about curtains like these:
http://www2.jcpenney.com/jcp/ProductsHOM.aspx?ItemID=12596f8&ItemTyp=G&GrpTyp=SIZ&ShowMenu=T&ShopBy=0&SearchString=curtains&RefPage=SearchDepartment.aspx&CmCatId=SearchResults&Search1Prod=True&S4Filter=N%7c4294967251%7cNtt%7ccurtains%7cNtk%7csearch_all%7cNao%7c0%7cNty%7c1%7csid%7c1167DEEFC087%7cNtx%7cmode%2bmatchallpartial%7cNtpr%7c1%7cNtpc%7c1%7cFN4294967251%7cbrown

I do not want the valance, I just want the curtains. So do I buy one or two?

My windows measure 36 x 49". Which size should I buy?

So I have to buy each curtain one and a half times bigger than my window? Since I have to buy two curtains for the one window, won't two curtains which are 1.5 bigger than my window be too big? I do want ripple.

Answer 1

The blackout thermals say they are sold as a pair. You'd only need to buy one set.
The size depends on how far past the window you want them to go.
I would measure 54 inches from the top of the window down. See where the bottom of that size curtain would reach and determine if you like the length.

Answer 2

Aesthetically, two will probably look better than one large single curtain hanging on one side of the window. As a rule of thumb, you will need a minimum of one and a half times the width of your window when deciding the width of the curtains. The more the material, the fuller the curtains.

Answer 3

The thermals are sold as a pair.
You need the 50 by 54" curtains for your window.
PS - I don't think they go very well with your bedding in other question.