Einführung
Whether you are a homeowner upgrading your space or a commercial builder sourcing units for a large development, 80% of installation issues stem from one mistake: inaccurate measurements. As a factory-direct manufacturer exporting thousands of French doors globally, we know that measuring for French doors requires more than just noting basic height and width—your technique must adapt to the specific door type. Below, we are sharing our factory-standard measurement protocols. Follow this concise guide to eliminate costly ordering errors, measure your rough openings like a pro, and guarantee a perfect fit for your project.
1. Know Your Door: 3 Classifications That Change How You Measure
Before grabbing your tape measure, you must identify exactly what type of French door you are ordering. This dictates your starting points:
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Prehung vs. Slab:
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Vormontierte Türen come already mounted in their frame with hinges.
Measurement rule: You must measure the structural “Rough Opening” of the wall. -
Plattentüren are just the doors themselves, without the frame.
Measurement rule: You must measure the exact dimensions of the existing door slab or the inside net width of the current frame.
-
Vormontierte Türen come already mounted in their frame with hinges.
- Innen vs. Außen: Exterior doors require a weatherproof threshold at the bottom, which completely changes how you calculate height (see Step 2 below).
- Einschwung vs. Ausschwung: This impacts your wall depth measurement and exterior waterproofing requirements (see Step 3 below).
2. The Standard Method: Measuring for a Prehung French Door
For 90% of new builds and full remodels, you will be ordering a prehung French door. Here is how to measure the Grobe Eröffnung (RO)—the structural hole in your wall.
Tools Needed for Accurate Measurement
Before you begin, ensure you have the right tools prepared. Using improper tools can lead to slight deviations, which often result in huge installation headaches later.
| Tool | Zweck | Pro Notes / Precautions |
| 25-Foot Steel Tape Measure | To measure the exact width, height, and depth of the rough opening. | Use a tape with a rigid blade that doesn’t bend easily when measuring heights. Keep the tape perfectly straight and taut. |
| Standard Level (4′ or 6′) | To check if the side studs are plumb (vertical) and the top header is level (horizontal). | Critical for identifying severe tilts early. A severely unlevel opening may require structural adjustments before ordering. |
| Framing Square (Optional) | To quickly check if the corners of your rough opening are true 90-degree angles. | Serves as a quick preliminary check before you perform the full “Diagonal Test” (explained in Section 4). |
| Notepad & Pen / B2B Template | To record measurements immediately and avoid costly memory errors. | Always write down all three measurements for width and height first, then circle the smallest value to submit to the factory. |
Step 1: Measure the Width
Measure the width of the rough opening at three points: the top, the middle, and the bottom.
- The Golden Rule: Notieren Sie die kleinste of these three measurements. Wood framing is rarely perfectly straight; using the smallest width ensures the door frame will slide into the opening without getting stuck.
Step 2: Measure the Height
Measure from the floor to the top header of the rough opening on the left side, the center, and the right side. Record the kleinste dimension.
💡 Manufacturer’s Pro Tip (Interior vs. Exterior): Where you start measuring determines if your door will actually fit!
- For Exterior Doors: Always measure from the Finished Floor (e.g., top of the hardwood or tile). Exterior doors require a thick, weatherproof sill/threshold at the bottom. If you measure from the subfloor during early construction, you must calculate and subtract the future flooring thickness.
- For Interior Doors: Depending on your threshold design, interior doors can sometimes be measured directly from the subfloor.
Step 3: Measure the Jamb Depth
Measure the total thickness of the wall, including the drywall or exterior siding on both sides. This ensures the door frame (jamb) sits perfectly flush with your walls.
💡 Manufacturer’s Pro Tip (Inswing vs. Outswing):
- Einschwingvorgang: Focus on achieving a flush finish with the interior drywall.
- Outswing (Exterior): You must account for exterior flashing and drip caps. Outswing exterior doors often require extended jambs and specific bumper thresholds to prevent water intrusion. Always specify the swing direction when submitting bulk orders to the factory!
3. The Exception: Measuring for a Slab Door Replacement
If your existing door frame is perfectly square and undamaged, and you only want to replace the two door panels, do not measure the wall! Instead, you need to replicate the existing doors.
- Exact Width & Height: Measure the exact width and height of the old door slabs down to the 1/16th of an inch.
- Türstärke: Standard interior French doors are usually 1-3/8″ thick, while exterior doors are 1-3/4″ thick.
- Hardware Locations (Crucial): Measure from the very top of the door down to the top of each hinge. Then, measure from the top of the door to the center of the boreholes (for the deadbolt and handle).
4. The Pro Check: Testing for Square and Plumb
Many buyers stop at width and height, only to discover their walls are crooked during installation. As manufacturers, we highly recommend the Diagonal Test.
Take your tape measure and measure from the top-left corner of the rough opening down to the bottom-right corner. Then, measure from the top-right to the bottom-left.
- If the two numbers are identical, your opening is perfectly square.
- If the numbers differ by more than 1/4 inch, your opening is “out of square.” You may need to order a slightly smaller door size to allow extra room for leveling shims during installation.
5. Standard Sizes & The Rough Opening Formula
Why can’t you just order a door that is the exact size of your wall opening? Because installers need extra space (clearance) to insert shims, level the frame, and apply insulation foam.
When international buyers submit Rough Opening data to our factory, our engineering team applies the following universal deduction standard to determine the actual factory net size:
- Required RO Width = Total Door Frame Width + 2 inches
- Required RO Height = Total Door Frame Height + 2.5 inches
Standard French Door Size Reference Chart
To help you determine if your opening fits a standard size or requires a custom build, refer to this common sizing chart for double French doors:
| Door Size (Nominal) | Door Frame Dimensions (W x H) | Required Rough Opening (W x H) | Beste Anwendung |
| 5’0″ x 6’8″ | 60″ x 80″ (Two 30″ Slabs) | 62″ x 82.5″ | Interior dining rooms, small patios |
| 6’0″ x 6’8″ | 72″ x 80″ (Two 36″ Slabs) | 74″ x 82.5″ | Standard master suites, main patios |
| 6’0″ x 8’0″ | 72″ x 96″ (Two 36″ Slabs) | 74″ x 98.5″ | High ceilings, grand entries |
| Custom Size | Varies based on design | Custom dimensions required | Non-standard renovations, unique builds |
To help project managers and homeowners calculate this instantly, we built this interactive tool:
French Door Rough Opening Calculator
Rough Opening Calculator
Calculate structural opening requirements based on standard slab sizes.
Required Dimensions
Total Door Frame Width
30.0″
Rough Opening Width (+2″)
32.0″
Rough Opening Height (+2.5″)
82,5″
* Standard factory tolerances applied. Always verify with local building codes.
6. Frequently Asked Questions (FAQs)
Q: Do I measure the door slab or the rough opening?
If you are buying a prehung door (door + frame), you must measure the structural rough opening of the wall. If you are keeping the old frame and just buying replacement slabs, measure the exact dimensions of the old doors down to the 1/16th of an inch.
Q: What is the rough opening for a standard 60″ x 80″ double French door?
Following the universal manufacturer’s formula, you should add 2 inches to the total frame width and 2.5 inches to the height. Therefore, a standard 60-inch by 80-inch double French door (two 30-inch slabs) requires a rough opening of exactly 62 inches wide by 82.5 inches high. This extra space allows your local contractors to properly use shims and insulation.
Q: Are French doors standard sizes for commercial projects?
Yes, standard heights are typically 80″ (6’8″) or 96″ (8’0″). Standard widths for double French doors are usually 60″ (two 30″ slabs) or 72″ (two 36″ slabs). However, as a custom manufacturer, Hotian Windows frequently manufactures custom sizes and specific door configurations tailored for global architectural projects and unique building codes.
7. Next Steps: Securing the Perfect Doors
For Homeowners & DIY Enthusiasts: Now that you have your precise Rough Opening dimensions, you are fully equipped to choose the perfect doors. We recommend taking these numbers to your local contractor or home improvement retailer to source your doors. Our pre-hung systems are engineered for seamless on-site installation by your local construction teams.
For Builders, Contractors & Building Material Distributors: Are you looking for a reliable manufacturing partner for your next residential development or commercial project? We engineer premium French door systems designed for maximum installation efficiency, drastically reducing local labor costs and on-site errors.
- Standardized & Custom Engineering: We easily accommodate international sizing standards (US, AU, EU) and complex architectural specifications.
- Streamlined Ordering: Stop guessing tolerances. Send us your rough openings, and our engineering team handles the factory net-size deductions and shop drawings.
Contact the engineering team at Hotian Windows today to discuss your project specifications and sizing requirements. Let us provide a comprehensive door schedule and factory-direct volume quote for your project within 24 hours.
Abschluss
Accurate measurement is the foundation of any successful door installation. By taking the time to understand your specific door type, correctly assessing the rough opening, and verifying the squareness of your frame, you eliminate the guesswork that leads to costly on-site delays. At Hotian Windows, we precision-engineer every French door to exact tolerances—which is why getting these initial numbers right is so critical. Whether you are upgrading a single entryway or sourcing for a massive commercial development, trusting the data ensures your project stays on time and on budget.
