To accomplish that you would need to make sure the curtain rod is at least 20 inches larger than the original window size of 48 inches or 68 inches.
Curtain rod length calculator.
Measure from the inner edge of one side of your frame to the other.
In the photo.
This will give you the length of your curtain rod.
Using a steel measuring tape measure the width of your windows inside your frame.
However because rods can be installed either inside below or above trim mount determining where you install your rod affects the length.
Source interior design by steven gambrel your drapery rod should generally be 10 15 inches longer on each side of the window to allow for the fabric to hang on each side.
How to measure for the correct curtain length grab your trusty measuring tape and take your measurements from the floor to where the rod will be placed.
Source the most common mistake that people make when measuring for off the shelf drapery is the rod itself.
Here is a simple chart.
We typically add 5 inches to each side of the frame for windows up to 50 inches wide then add another 2 inches for each additional 10 inches of window frame width.
You calculate curtain length with double curtain rods the same way you calculate the length for single curtain rods measuring from where you ll install the rods to where you want the curtains to.
Wallace racing back to calculators this calculator will figure the rod length using your inputs.
This look offers a few advantages.
Input all info please.
Please note that the calculation of the stack back width is only an estimate stack back can fluctuate depends on factors such as puddling fabrics lining options curtain rods brackets and rings.
Stack back is the amount of space the curtains occupy when in the fully open position.
The curtain will hang 3 inches below the bottom of the window sill.
Determine rod length before you measure your window for width it s best to choose the length of your curtain rod.
For a more advanced calculator try this one.
Curtain rods are typically extended 3 to 6 inches past a window frame.
I see this so often i decided to write a post so that at least all my readers will be in the know.
To make your windows appear wider and higher as you should add a few inches to your measurements.
In traditional style the curtain rod is about 6 inches above the top of the window and it extends beyond the window 3 inches on each side.