Measuring for bifold doors is not complicated. It does require attention. Get the width or height wrong by a little and you get gaps, binding, or a door that will not close. Here is what it takes to measure an opening for aluminum bifold doors: the tools you need, how to record your numbers, and what to do if your opening is out of square.
WANJIA Hiseng makes aluminum bifold doors in 68, 75, 80, and 88 series. Each series has its own frame depth and hardware needs. The measurements you send help us confirm the right product for your project. We also give measurement guidance and remote assistance after you place an order.
What You'll Need
A steel tape, pencil, notepad, and a level. That covers it. A laser measure is faster if you have one, but a regular tape works for most openings. Keep the tape straight, not kinked. Use the same one for every measurement. That way the numbers agree with each other.
Step 1: Width
Measure the rough opening at top, middle, bottom. That is the framed hole in the wall before any door goes in. Do not measure the old door or the trim. Write down all three numbers. If they differ, use the smallest one. That's your width.
Here's why. The new frame has to fit through the narrowest part of that opening. For a typical aluminum bifold door, the frame sits inside with a small gap for shims and insulation. The exact gap depends on the series and how it is installed. A common practice is to allow about 10 mm on each side. Your supplier will confirm the required rough opening based on the door size you order, so get that number from them before you build anything.
Measuring height
Check the height in three places: left, middle, right. Measure from finished floor to the top of the rough opening. Use the smallest number, same as before. If the floor is out of level, write down by how much. A folding patio door needs a level bottom track, so you might have to fix the floor first. For new construction, measure from the subfloor instead of the finished floor, and tell your supplier what flooring will go on top.
Step 3: Check if the Opening Is Square
Square means the diagonals match. Measure corner to corner both ways, top left to bottom right, then top right to bottom left. If those two numbers differ by more than 6 mm, the opening is out of square. You can still fit a bifold. But you'll need to adjust the frame or shim it with tapered pieces. Record both diagonals. Hand them to your supplier.
Step 4: Measure the Depth
Rough opening depth is interior wall face to exterior wall face. The frame has to fit that thickness. A standard 2x4 or 2x6 wall usually works, but thicker walls may need extension jambs. Aluminum bifold frame depth changes by series. The 88 series uses a 2.0 mm profile with 2.2 mm local reinforcement. The overall frame depth is larger, so check the product specifications for the series you are considering.
Measuring Mistakes That Cost You
People measure the old door and run into trouble. That old door was shimmed or trimmed to fit an opening that was never square to begin with. Measure once and you are asking for a bad fit. Take three measurements for width and height, then use the smallest. And do not forget the flooring. Tile or hardwood going in after the door means the finished floor height will cut into your available height. Tell your supplier the planned floor thickness.
Recording measurements
Write everything down in millimeters or inches. Pick one. Do not switch. Log the three widths, three heights, two diagonals, and wall depth. Note any pipes, wires, or structural posts near the opening. If the opening is not square, say exactly how far out it is.
A quick sketch with the dimensions saves time. Send that with your quote request to WANJIA Hiseng. We will check the numbers and confirm the right door size for your project.
After You Measure
Take your opening size and check it against what we actually build. The 88 series folding door takes sash widths from 500 to 900 mm and heights from 1900 to 3000 mm. Different series, different ranges. If your opening is bigger than the max panel, the door just gets more panels. Smaller openings may need a custom size. Numbers close? We can suggest the best setup.
Once you order, you get installation videos and instructions. Run into trouble on site, our technical team can help remotely. We do not send installers to your site. But we can help you get the numbers right before you order.
Measuring for Different Door Types
Folding patio doors, aluminum clad wood doors, French doors, and sliding patio doors all measure the same way. What changes is frame depth and track system, and that changes the height measurement.
Bifold doors can have the bottom track recessed into the floor or surface mounted. A flush threshold means you need a floor recess. Sliding door tracks are usually surface mounted, so height runs from floor to top of opening. Check the requirements for your door type before you order.
When to Bring in a Pro
If the opening is badly out of square, the wall isn't plumb, or you're not sure about structural issues, get a local contractor or installer in. They can check load-bearing needs and fix the framing if it needs fixing. But for most standard openings, a careful DIY measurement works. Just follow the steps and check your numbers twice.
Measuring a Bifold Door: Step by Step
| Step | What to Measure | How Many Points | What to Record |
|---|---|---|---|
| 1 | Width of rough opening | 3 (top, middle, bottom) | Smallest measurement |
| 2 | Height of rough opening | 3 (left, center, right) | Smallest measurement |
| 3 | Diagonals for square | 2 (corner to corner) | Both measurements |
| 4 | Wall depth | 1 (at each side) | Depth in mm or inches |
Work down the table in order: width first, then height, then square, then depth. Check off each step as you finish it so you don't repeat or skip one. You'll end up with six numbers to hand to whoever is ordering the doors.
Final Tips
Measure twice, order once. Take your time. Don't rush. On a replacement, pull the interior trim first. That exposes the rough opening. On a new opening, use the framing dimensions the door manufacturer specifies for that product. And always send your measurements to your supplier before finalizing the order, so WANJIA Hiseng can review your numbers and confirm the right door size for your aluminum bifold door project.
Bifold Door Opening Size: What Your Numbers Mean for the Order
Your rough opening numbers are not the size of the door you order. The opening is the framed hole. The door is the finished unit that slides into it. Subtract for the frame, the shims, and the seal. Ten millimeters per side is a common allowance, but the exact deduction depends on the series. Get that figure from your supplier before you build anything.
Panel count and sash width
Width decides panel count. The 88 series folding door takes sash widths from 500 to 900 mm and heights from 1900 to 3000 mm. Wider opening, more panels. A narrow one may need a custom size. Send three width readings, three height readings, and both diagonals. We check the panel layout against your opening.
Same logic whether you are pricing aluminum bifold doors, folding patio doors, aluminum clad wood doors, French doors, or sliding patio doors. Frame depth and track system differ, so the height deduction differs too. A recessed bottom track eats floor depth. A surface mounted track does not. Tell your supplier the planned flooring thickness before you order.