Measure the width and height of the actual glass opening, not the frame
The most common mistake is measuring the frame around the glass instead of the glass itself. Your drapes need to cover the glass opening where light comes through, so start there. Close the door fully and look at where the glass begins and ends—that is what you are measuring.
Use a steel tape measure, not a fabric one. Steel stays rigid and gives you an accurate reading. Measure the width at three points: top, middle, and bottom of the glass opening. Write down all three numbers. If they differ, use the smallest measurement—this ensures your drapes will cover the full opening without gaps.
For height, measure from the top of the glass opening to the bottom at three points: left side, center, and right side. Again, write all three and use the smallest. Patio door glass openings are often slightly uneven because the frame settles over time, so checking multiple points catches this.
Key Takeaways
- Measure the glass opening itself, not the frame or the entire door unit, at three points in each direction.
- Use a steel tape measure and record the smallest measurement in each direction to account for uneven frames.
- Decide whether you want drapes to cover just the glass or extend beyond it to the wall, as this changes your final measurements.
- Add extra length for hems and rod pockets—typically 4 to 6 inches total—before ordering or cutting fabric.
- Measure twice and write everything down; mistakes in measurement are the leading cause of drapes that do not fit properly.
Decide whether drapes cover glass only or extend to the wall
You have two common approaches. The first is to cover only the glass opening—drapes hang from the top of the glass to the bottom and are as wide as the glass. This is the simplest and works well if your patio door frame is in good condition and you like a clean, minimal look.
The second approach is to extend drapes beyond the glass to the wall on both sides and above the door. This makes the door look larger and blocks more light and heat. If you choose this route, you need to decide how far beyond the glass you want to go—typically 4 to 8 inches on each side and 6 to 12 inches above. Measure from the glass edge to where you want the rod to sit, then add those measurements to your glass opening measurements.
Most people choose the extended approach for patio doors because it improves insulation and gives a more finished appearance. If that is your plan, measure where the rod will hang before you buy or cut anything.
Account for rod pockets, hems, and hardware
A rod pocket is the fabric sleeve at the top of the drape that the rod slides through. Standard rod pockets are 2 to 3 inches deep. If your drapes have a rod pocket, you need to add that depth to your height measurement so the drapes hang at the right level. For example, if your glass opening is 60 inches tall and you want a 2.5-inch rod pocket, order or cut fabric that is 62.5 inches tall before hemming.
Hems at the bottom add another 2 to 4 inches depending on how finished you want them to look. If you are buying ready-made drapes, the manufacturer has already accounted for this. If you are cutting fabric or having drapes custom-made, tell the person doing the work your exact glass opening height, and they will add the rod pocket and hem.
For width, most drapes need extra fabric so they gather and look full when closed. A common rule is to order drapes that are 1.5 to 2 times the width of your opening. So if your glass is 36 inches wide, order drapes that are 54 to 72 inches wide. This varies by fabric weight and style, so check the product description or ask the seller.
Measure from the rod location, not the glass, if the rod is already installed
If you already have a curtain rod hanging above your patio door, measure from the rod itself, not from the glass opening. Measure the distance from the rod down to where you want the drapes to end—usually 1/2 inch above the floor or the bottom of the glass opening, whichever looks better to you.
For width, measure the length of the rod itself. That is the span your drapes need to cover when closed. If the rod extends beyond the glass opening on both sides, your drapes will too, which is fine—it actually improves light blocking.
If you do not have a rod yet and are installing one, mount it first, then measure from the rod to determine drape length. This prevents the mistake of measuring the glass opening and then discovering the rod is mounted higher or lower than you expected.
Check for obstacles like handles, locks, and hardware
Patio doors have handles, locks, and sometimes blinds or shades built into the frame. Before you finalize your measurements, open and close the door fully and note where these obstacles are. If your drapes will hang inside the frame (covering only the glass), make sure they do not interfere with the handle or lock when the door opens.
If you have blinds or a shade inside the glass, you have two choices: hang drapes outside the frame so they do not touch the blinds, or remove the blinds and hang drapes inside the frame. Hanging outside the frame is simpler and more common for patio doors.
Measure the depth of the frame as well—how far it sticks out from the wall. This matters if you are mounting a rod inside the frame. If the frame is shallow, a standard rod may not fit, and you will need a shallow-mount rod or to mount the rod on the wall outside the frame instead.
Write down all measurements and double-check them
Create a straightforward written record: glass width (top, middle, bottom), glass height (left, center, right), rod location if applicable, and any obstacles. Take a photo of your patio door with the tape measure visible if you can—this helps you remember the layout when you are shopping or ordering.
Measure a second time before you buy or cut anything. Mistakes at this stage are expensive and frustrating. If you are ordering custom drapes, send your measurements to the seller and ask them to confirm they understand where the rod will be and how much the drapes should extend beyond the glass.
If you are buying ready-made drapes, check the product dimensions carefully. Manufacturers list the width and length of the finished drape, not the glass opening size. You need to work backward from the finished drape size to see if it will fit your opening with the right amount of fullness.
Frequently Asked Questions
Should drapes go all the way to the floor or stop at the windowsill?
For patio doors, most people hang drapes to the floor or 1/2 inch above it. This looks more formal and blocks more light and drafts. Stopping at the sill is less common for patio doors because it can look unfinished, but it works if you prefer a shorter look or have furniture in the way.
What if my patio door measurements are not even on all three sides?
Uneven measurements are normal in older homes. Always use the smallest measurement so your drapes cover the entire opening without gaps. If the difference is more than 1/2 inch, the frame may be settling or damaged—consider having it checked by a professional before hanging heavy drapes.
Do I need to measure differently for sliding glass doors versus French doors?
The measuring process is the same for both. The difference is that French doors have multiple panes and a center frame, so you may want drapes that cover the entire door unit rather than individual panes. Measure the full width and height of both doors together if you want one set of drapes covering both.
Can I use the same drapes on multiple patio doors if they are different sizes?
Only if the doors are exactly the same size. If they differ by more than 1 inch in width or height, you will have gaps or bunching. It is better to measure each door separately and order drapes for each one, or choose a style that can be adjusted or layered.
What happens if I order drapes that are too wide or too narrow?
Drapes that are too narrow will not close fully or will have gaps at the sides. Drapes that are too wide will bunch heavily when closed and may not fit on the rod. Most sellers allow returns or exchanges within a set period, so check the return policy before ordering, especially for custom work.