Things You'll Need
Large flat work surface
Blackout curtains use an extra thick lining to help block out as much light as possible from a window. They can be very useful for people who need to sleep while it's still light outside, or for those who have a bright streetlight shining through their window at night. Blackout curtains can, in theory, block out all light if they fit perfectly over the window, but in most cases some light will still seep in around the edges of the curtain. You can buy blackout backing from fabric stores with a home decor selection, or you can order it online. To hang up the curtains, you'll need a basic curtain rod with no hooks that's slightly wider than the window. Since blackout curtains are extra heavy, make sure to buy a sturdy rod.
Install the curtain rod above the window. Since blackout curtains are thick, you may want to make the rod several inches wider than the window on each side, so that when you slide the curtains open, they won't be covering too much of the window.
Measure from the top of the curtain rod to a few inches below the window frame (or lower if you want the curtains longer). Measure the width of the curtain rod.
Calculate how much fabric you need by multiplying the window width by 1.5 and adding 6 inches, and adding 7 inches to the window height. To make two curtains for the window, divide the width calculation by two. For example, for a 64 inch square window, you'd need two pieces of fabric, each about 54 inches wide and 71 inches (about 2 yards) long, or 4 yards total.
Buy curtain fabric and matching thread. Buy the same amount of blackout backing.
Cut the curtain fabric to the size you calculated in Step 3. Cut the blackout backing 3 inches narrower and 3 inches shorter than the curtain fabric.
Spread out the curtain fabric right side down on a large flat surface. Place the blackout backing right side up on the curtain fabric. Center the blackout backing on the curtain fabric, so that you have 1 1/2 inches of extra fabric on each side.
Fold one edge of the curtain fabric over 3/4 inch, so that the cut edge of the curtain fabric is even with the edge of the blackout backing. Fold the curtain fabric over another 3/4 inch, over the edge of the blackout backing.
Press the folded edge, then pin it in place. Stitch along the folded edge of the curtain fabric using matching thread.
Repeat Steps 7 and 8 for the other edges of the curtain.
Fold the top edge of the curtain over 4 inches toward the backing. Make sure the fold is even all the way across. Pin the fold in place, then stitch along the bottom edge of the folded fabric.
Sew the second curtain the same way. Insert the curtain rod through the folded areas at the top of the curtains.
To keep the blackout curtains open, you may want to add tiebacks.
Use caution when working with scissors, pins, irons and sewing machines.