Measure the width and height of your patio door opening, then add extra inches for the rod placement and fabric fullness you want

The three measurements you need are the width of the glass itself, the height from top to bottom of the glass, and the distance from the floor to where you want the curtain to end. Write these down in inches. Do not measure the frame or trim—measure only the glass opening. Use a metal tape measure, not a cloth one, because cloth stretches and gives you wrong numbers.

Stand directly in front of the door and hold the tape measure level and straight. Measure the width at the top, middle, and bottom of the glass—patio door openings are sometimes slightly wider at one point than another. Use the smallest number you get, because that is the measurement your rod and curtains have to fit through. For height, measure from the very top of the glass to the very bottom, again in at least two spots if the door frame is old or uneven.

Key Takeaways

  • Measure only the glass opening itself, not the frame or trim, using a metal tape measure held level and straight.
  • Take width measurements at the top, middle, and bottom of the glass and use the smallest number to account for uneven frames.
  • Decide whether you want curtains that stop at the sill, reach the floor, or puddle slightly on the floor, because this changes your height measurement by several inches.
  • Add 4 to 8 inches to your width measurement for the rod to extend beyond the glass on both sides, which makes the door easier to open and the window look wider.
  • Multiply your final width by 1.5 to 2.5 depending on how full and gathered you want the curtains to look when they are closed.

Decide where you want the curtain to end

Curtains can stop at three different places: at the sill (the bottom edge of the glass frame), at the floor, or pooling slightly on the floor. Each choice changes your height measurement. Measure from the top of the glass to the sill if you want the curtain to stop there. Measure to the floor if you want it to hang straight down without touching the ground. Measure to 1 to 2 inches below the floor if you want a slight pool of fabric on the floor—this is a formal look and requires more fabric.

Most people choose floor-length for patio doors because it looks balanced with the size of the opening and makes the room feel taller. Sill-length is practical if you have a patio or deck outside and need to open the door often. Write down which option you are choosing before you move to the next step, because it affects every measurement that follows.

Add inches for rod placement beyond the glass

The curtain rod should extend past the edge of the glass on both sides so the curtains can open fully without blocking the view or the door handle. Add 2 to 4 inches on each side of your glass width measurement. If your patio door is in a corner or tight space, add only 2 inches per side. If you have room and want the curtains to look more dramatic when open, add 4 inches per side.

For example, if your glass is 36 inches wide and you add 3 inches on each side, your rod needs to be 42 inches long (36 + 3 + 3). This is the measurement you will use when you shop for a curtain rod. Write this number down separately from your glass width, because you will need both.

Calculate fabric width for fullness and gathering

Curtains look better when they have folds and gather, not when they hang flat and tight. To get that gathered look, you multiply your rod width by a fullness multiplier. The multiplier depends on the fabric weight and the look you want. Lightweight fabrics like voile or linen need a multiplier of 2 to 2.5 because they do not hold folds as well. Medium-weight fabrics like cotton or linen blends use 1.5 to 2. Heavy fabrics like velvet or blackout fabric use 1.5 because they are stiff enough to look good with less gathering.

If your rod is 42 inches and you want medium fullness with a medium-weight fabric, multiply 42 by 1.75 to get 73.5 inches of total fabric width. This is the width you will order when you buy curtain panels. Most curtain panels come in standard widths of 50, 84, or 96 inches, so you may need two panels to reach your target width, or you may need to have panels sewn together.

Account for seams and hems when ordering panels

When you order curtain panels, the width listed on the label is the finished width after the panel is hemmed on both sides. Each side hem takes up about 1 to 1.5 inches of fabric. If you order a panel that says 50 inches finished width, the actual fabric before hemming is wider, but after hemming it will be 50 inches. This is the number you use when you calculate whether you need one panel or two.

If your calculated fabric width is 73.5 inches and you want to use two 50-inch panels, that gives you 100 inches total, which is more than enough and will create very full, gathered curtains. If you want a less full look, you could use one 84-inch panel instead. Check the panel dimensions before you order to make sure the finished width matches what you need.

Measure the distance from rod to floor for panel length

Once you know where you want your rod to hang, measure from the rod height down to your chosen endpoint—sill, floor, or pooling point. This is your panel length. If you are hanging the rod at the very top of the glass frame, measure from that point straight down. If you are hanging the rod above the frame (which is common for a more formal look), measure from the rod location down instead.

Curtain panels are sold in standard lengths: 63, 84, 96, 108, and 120 inches. Measure carefully and round up to the next standard length if your measurement falls between sizes. For example, if you measure 85 inches, order 96-inch panels. You can always hem them shorter, but you cannot add fabric if they are too short. Most curtain panels come with a 4-inch hem already sewn in at the bottom, so the finished length is 4 inches shorter than the label says—check the product details before you order.

Create a measurement worksheet for shopping

Write down these four numbers before you go shopping or order online: (1) rod width in inches, (2) total fabric width you need in inches, (3) panel length in inches, and (4) number of panels. Include notes about the endpoint you chose (sill, floor, or pooling) and the fullness multiplier you used, so if you need to reorder or adjust, you have a record of your choices.

Take a photo of your patio door with the tape measure visible in the frame. This helps you remember the scale of the opening and makes it easier to show a salesperson or fabric informed what you are working with. Bring both the worksheet and the photo when you shop, and you will have everything you need to find curtains that fit your space.

Frequently Asked Questions

Should I measure inside the frame or outside the frame?

Measure the glass opening itself, not the frame trim. The glass is what you see and what determines how much light comes in. The frame is decorative and varies by door style. Measuring the glass gives you the true opening size.

What if my patio door is not perfectly square?

Older doors and doors in settled houses are often slightly uneven. Measure at the top, middle, and bottom of the width and at the left, center, and right of the height. Use the smallest width measurement and the largest height measurement. This ensures your rod and curtains fit without binding or leaving gaps.

Do I need to account for the curtain rod thickness?

Most standard curtain rods are 1 to 1.5 inches in diameter. This thickness is already accounted for in the rod width measurement you took. You do not need to add extra inches for the rod itself—just for the rod to extend past the glass on both sides.

Can I use one very wide curtain panel instead of two narrower ones?

Yes, if you can find a panel wide enough. Single panels are less common in standard sizes, but custom curtain makers can sew a single panel to your exact width. Two panels sewn together give you more flexibility in fabric choice and are usually less expensive than one custom panel.

What happens if I order curtains that are too long?

You can hem them shorter yourself with a needle and thread, or take them to a tailor or dry cleaner who does alterations. Hemming costs between $15 and $40 depending on the fabric weight and the tailor. It is easier and cheaper to hem them shorter than to add length, so always round up when choosing a standard panel length.