Custom Door Sizes & Specifications: What B2B Buyers Need to Know When Ordering from China

Quick Facts	Details
Factory:	Bestop Door Factory
Standard Sizes:	Per EN, ANSI, AS standards
Custom Size Range:	600mm–1200mm W × 1800mm–2400mm H
Thickness Options:	35mm, 40mm, 44mm, 50mm, custom
Tolerance:	±1.5mm
MOQ for Custom Sizes:	50 units

1. Introduction: Why Getting Specifications Right Saves Money and Delays

As an architect, contractor, or B2B buyer, you understand that doors are more than just entry points; they are critical components of a building's design, functionality, and safety. When sourcing doors, especially custom solutions, from a global manufacturing hub like China, precision in specifications is paramount. Misunderstandings or inaccuracies in custom door sizes specifications China can lead to costly delays, rework, and ultimately, project budget overruns.

At Bestop Door Factory, we specialize in manufacturing high-quality doors tailored to your exact project requirements. This comprehensive guide is designed to equip you with the knowledge needed to confidently specify and order custom doors, ensuring a smooth and efficient procurement process. We'll delve into standard regional sizes, explain custom dimension capabilities, detail thickness options, and provide a clear framework for technical specification, helping you avoid common pitfalls.

2. Standard Door Sizes by Region

While custom doors offer unparalleled design flexibility, understanding regional standard sizes provides a valuable baseline and can sometimes simplify procurement. Many projects can utilize a mix of standard and custom sizes.

Europe (EN Standard)

European door sizes are typically specified in millimeters and often adhere to EN (European Norm) standards, though variations exist by country.

Type	Width (mm)	Height (mm)	Common Imperial (approx.)
Standard Internal	626, 726, 826, 926	2040	24.6", 28.6", 32.5", 36.5" W x 80.3" H
Common External	826, 926	2040	32.5", 36.5" W x 80.3" H
Fire Rated (typical)	826, 926, 1050	2040, 2100	32.5", 36.5", 41.3" W x 80.3", 82.7" H

North America (ANSI/NFPA)

North American door sizes are predominantly specified in inches, often with a focus on imperial measurements, and adhere to standards set by organizations like ANSI (American National Standards Institute) and NFPA (National Fire Protection Association).

Type	Width (inches)	Height (inches)	Common Metric (approx.)
Standard Internal	24, 28, 30, 32, 34, 36	80	610, 711, 762, 813, 864, 914mm W x 2032mm H
Common External	30, 32, 36	80	762, 813, 914mm W x 2032mm H
Commercial (typical)	36, 42, 48	80, 84, 96	914, 1067, 1219mm W x 2032, 2134, 2438mm H

Australia/NZ (AS Standard)

Australia and New Zealand primarily use metric measurements, with door sizes often aligning with AS (Australian Standards).

Type	Width (mm)	Height (mm)	Common Imperial (approx.)
Standard Internal	620, 720, 820, 920	2040	24.4", 28.3", 32.3", 36.2" W x 80.3" H
Common External	820, 920	2040	32.3", 36.2" W x 80.3" H

Middle East & Asia (Common Sizes)

While there isn't a single universal standard across the Middle East and Asia, many countries adopt sizes influenced by European or North American standards, or have their own common dimensions. Metric is generally preferred.

Type	Width (mm)	Height (mm)	Common Imperial (approx.)
Common Internal	700, 800, 900	2000, 2100	27.6", 31.5", 35.4" W x 78.7", 82.7" H
Common External	900, 1000	2100, 2200	35.4", 39.4" W x 82.7", 86.6" H

3. Custom Door Dimensions: What Can Be Changed?

When standard sizes don't fit your architectural vision or structural constraints, custom doors are the solution. Bestop Door Factory excels in manufacturing doors to your precise specifications.

Width Range

Our custom door width capabilities are extensive, typically ranging from 600mm (23.6 inches) up to 1200mm (47.2 inches) for single leaf doors. For wider openings, we can manufacture double leaf doors or provide solutions with sidelights and transoms. It's crucial to specify whether the width refers to the door slab itself or the overall frame opening.

Height Range

Custom door heights can vary from 1800mm (70.9 inches) up to 2400mm (94.5 inches). For heights exceeding 2400mm, we can often incorporate transoms above the door to achieve the desired overall opening height. Again, clarify if this is the slab height or the frame height.

Thickness Options

Door thickness is a critical specification, impacting structural integrity, acoustic performance, and fire rating.

Our standard thickness options include:

• 35mm (1 3/8 inches): Common for interior residential doors.
• 40mm (1 9/16 inches): A versatile thickness for many interior and light commercial applications.
• 44mm (1 3/4 inches): Standard for many commercial and fire-rated doors (e.g., FD30/60 in the UK, 20/45/60-minute in the US).
• 50mm (1 15/16 inches): Often used for high-performance acoustic doors, security doors, or specific fire ratings.

We can also accommodate other custom thicknesses based on project requirements, subject to material availability and performance testing.

Frame vs. Slab Dimensions

A common point of confusion is whether dimensions refer to the door slab itself or the overall frame opening. Always specify clearly:

• Door Slab Dimensions: The exact width, height, and thickness of the door panel.
• Frame Opening Dimensions: The clear opening required for the door and frame assembly. This is often referred to as "rough opening" in North America.
• Overall Frame Dimensions: The total external dimensions of the door frame, including jambs and head.

Providing a detailed drawing with these dimensions clearly marked is the best practice.

4. Door Thickness Guide: Which Thickness for Which Application?

The appropriate door thickness depends heavily on its intended use and required performance characteristics.

• 35mm (1 3/8 inches):

  • Application: Standard interior doors for residential properties, closets, and light-duty commercial interiors where sound insulation and fire rating are not primary concerns.
  • Benefits: Lighter weight, more cost-effective.

• 40mm (1 9/16 inches):

  • Application: Mid-range interior doors, some apartment entry doors, and light commercial applications. Offers slightly better durability and sound dampening than 35mm.
  • Benefits: Good balance of cost, durability, and moderate performance.

• 44mm (1 3/4 inches):

  • Application: Standard for many commercial interior and exterior doors, fire-rated doors (e.g., FD30, 20-minute, 45-minute), and doors requiring enhanced security or acoustic properties.
  • Benefits: Robust, excellent for fire ratings, improved sound insulation and security. This is a very common thickness for project work.

• 50mm (1 15/16 inches) and above:

  • Application: High-performance acoustic doors, high-security doors, specialized fire-rated doors (e.g., FD60, 60-minute, 90-minute), and heavy-duty industrial applications.
  • Benefits: Superior sound attenuation, maximum security, highest fire ratings.

When specifying thickness, always consider the complete door system, including the frame, hardware, and seals, as these components work together to achieve desired performance levels.

5. How to Specify a Door Order: The Technical Brief

A clear, comprehensive technical brief is the cornerstone of a successful custom door order. It minimizes ambiguity and ensures Bestop manufactures exactly what you need.

Required Information Checklist

Category	Details to Provide	Example / Notes
Door Type	Single leaf, double leaf, sliding, folding, pivot, louvered, etc.	Single leaf, hinged, in-swing
Dimensions	- Door Slab Width (W) - Door Slab Height (H) - Door Slab Thickness (T) - Wall Opening Width - Wall Opening Height - Frame Profile Dimensions (if custom)	W: 900mm, H: 2100mm, T: 44mm. Wall opening: 920x2120mm
Material	- Core material (solid wood, particleboard, mineral core, honeycomb, etc.) - Facing material (MDF, plywood, HPL, veneer, metal sheet) - Finish (paint, lacquer, laminate, stain)	Solid particleboard core, 6mm MDF facing, primed for site painting
Frame Details	- Frame material (solid wood, MDF, steel) - Frame profile (rebated, flush, architrave type) - Wall thickness door is installed into	Solid timber frame, rebated, for 100mm (4 inch) wall
Hardware Prep	- Hinge type & quantity (e.g., 3 x 4" butt hinges) - Lock type & backset (e.g., mortise lock, 60mm backset) - Lever/handle type - Closer prep, peephole, kick plate, vision panel cutouts, etc.	Prep for 3 x 100x75mm butt hinges, mortise lock with 60mm backset, no closer prep
Performance	- Fire Rating (e.g., FD30, 45-minute) - Acoustic Rating (e.g., STC 35dB, Rw 35dB) - Security Rating - Weather Resistance (for exterior doors)	FD30 (EN 1634-1), STC 35dB
Handing	Left-hand reverse, right-hand reverse, left-hand, right-hand	Left-hand, in-swing (viewed from exterior/pull side)
Quantity	Number of units per size/type	15 doors
Project Details	Project name, location, specific certifications required	"Grand Tower Residential", Dubai, UAE, ISO 9001 certified factory
Packaging	Individual carton, palletized, bulk	Individual carton with corner protection

Drawing Format Requirements

For custom door sizes specifications China, detailed drawings are indispensable. We prefer CAD drawings (.dwg, .dxf) or high-resolution PDF drawings. Each drawing should include:

• Plan View: Showing door swing, frame, and wall relationship.
• Elevation View: Showing door face, vision panels, and hardware locations.
• Section Details: Critical for frame profiles, door thickness, and any specific construction details.
• Dimensioned Drawings: Clearly indicating all critical measurements (slab, frame, opening, hardware centerline).
• Hardware Schedule: A list of all hardware to be prepped for, including specific models if available.

Tolerances and Allowances

Bestop Door Factory adheres to strict quality control standards. Our standard manufacturing tolerance for door dimensions is ±1.5mm (±0.06 inches). This allowance is critical for proper installation and operation. For highly sensitive applications, please discuss stricter tolerances with our sales team, which may incur additional costs.

6. Fire Door Specifications: Special Requirements

Fire doors are life-safety products and require meticulous specification. When ordering custom fire doors, ensure you provide:

• Required Fire Rating: Specify the duration (e.g., FD30, FD60, 20-minute, 45-minute, 90-minute) and the relevant standard (e.g., EN 1634-1, UL 10C, BS 476 Part 22).
• Door Core Material: Fire-rated cores are specific (e.g., mineral board, intumescent particleboard).
• Intumescent Strips and Smoke Seals: These are integral to fire door performance and must be specified, often factory-fitted.
• Hardware: Only fire-rated hardware (hinges, locks, closers, vision panels) can be used. Prepping for non-fire-rated hardware will compromise the door's integrity.
• Glazing: If vision panels are required, the glass must be fire-rated, and the glazing system must be approved for fire doors.
• Frame: The frame must also be fire-rated and compatible with the door assembly.

Bestop can provide fire-rated door sets (door slab, frame, and hardware prep) that meet international standards. Always consult local building codes and regulations for specific requirements.

7. Acoustic Door Specifications

Acoustic doors are designed to reduce sound transmission between spaces. Key specifications include:

• Sound Transmission Class (STC) or Weighted Sound Reduction Index (Rw): Specify the desired decibel reduction (e.g., STC 35dB, Rw 38dB). Higher numbers indicate better sound insulation.
• Door Construction: Acoustic doors typically feature a dense, multi-layered core, often with specific mass-loaded vinyl or other sound-absorbing materials.
• Thickness: Generally, thicker doors (44mm, 50mm, or more) provide better acoustic performance.
• Sealing Systems: Perimeter seals (gaskets), automatic drop seals at the bottom, and a tightly sealed frame are crucial for acoustic performance. Gaps compromise sound insulation significantly.
• Hardware: Heavy-duty hinges and specialized acoustic-rated hardware may be required.

Achieving high acoustic ratings requires a holistic approach, considering the entire door assembly, including the frame and installation.

8. Common Specification Mistakes and How to Avoid Them

Even experienced buyers can make mistakes. Here are some common pitfalls and how to prevent them:

• Confusing Slab vs. Opening Dimensions: Always clarify if dimensions refer to the door slab, the frame's clear opening, or the overall frame size. Use detailed drawings.
• Incomplete Hardware Prep Details: Simply stating "standard hardware" is insufficient. Provide a hardware schedule with specific types, quantities, and locations (e.g., hinge centerline from top/bottom).
• Neglecting Handing: Incorrect handing leads to doors swinging the wrong way. Clearly specify left-hand, right-hand, in-swing, out-swing, from a consistent reference point (e.g., viewed from the exterior).
• Overlooking Wall Thickness: The frame profile must match the wall thickness. Provide this critical dimension.
• Ignoring Performance Requirements: For fire or acoustic doors, simply stating "fire door" or "soundproof" is not enough. Provide specific ratings (e.g., FD60, STC 40).
• Assuming Standard Finishes: Be explicit about the desired finish (e.g., specific RAL color, wood veneer species and cut, laminate pattern).
• Lack of Clear Communication: Use clear, unambiguous language. When in doubt, ask for clarification. Visual aids like marked-up photos or sketches are helpful.

9. How Bestop Handles Custom Specifications

At Bestop Door Factory, our process for handling custom door sizes specifications China is designed for precision and efficiency:

1. Initial Inquiry & Project Review: You provide your initial requirements, including project scope, door types, and any preliminary dimensions.
2. Detailed Specification Submission: You submit your comprehensive technical brief, including drawings, material preferences, performance requirements, and hardware schedules.
3. Technical Review & Clarification: Our engineering team reviews your specifications. We will proactively identify any ambiguities, potential conflicts, or areas requiring further detail, reaching out for clarification.
4. Shop Drawing Creation: Based on the finalized specifications, we produce detailed shop drawings for your approval. These drawings illustrate every aspect of the door, frame, and hardware prep.
5. Client Approval: You review and approve the shop drawings. This is a critical step where any final adjustments are made before production.
6. Sampling (Optional): For large or complex orders, we can produce a prototype or sample door for your evaluation and approval.
7. Manufacturing & Quality Control: Production commences under strict quality control protocols, ensuring adherence to the approved specifications and tolerances.
8. Packaging & Shipping: Doors are carefully packaged for international transit and shipped according to your logistics requirements.

We pride ourselves on our ability to translate complex architectural designs into high-quality, functional doors. We also offer comprehensive OEM/ODM door manufacturing services to meet diverse project needs.

10. FAQ (5 questions about custom door sizes)

Q1: What is the minimum order quantity (MOQ) for custom door sizes? A1: For custom door sizes, our standard MOQ is 50 units. However, this can be flexible depending on the complexity and type of door. Please contact our sales team to discuss your specific project needs.

Q2: Can Bestop accommodate custom door thicknesses outside of 35mm, 40mm, 44mm, and 50mm? A2: Yes, we can often accommodate other custom thicknesses. This will depend on the core material, required performance (e.g., fire rating), and overall project volume. Please provide your exact thickness requirement for evaluation.

Q3: How do I specify hardware prep for custom doors? A3: The best way is to provide a detailed hardware schedule listing each item (hinges, lockset, closer, etc.), its specific model or type, and clear dimensioned drawings showing its exact location on the door and frame (e.g., centerline of lock from bottom of door, hinge cutouts from top/bottom).

Q4: What's the difference between door slab size and rough opening size? A4: The door slab size refers to the actual dimensions of the door panel itself. The rough opening size is the larger structural opening in the wall that accommodates the entire door frame and door assembly. The frame will sit within the rough opening, and the door slab will sit within the frame.

Q5: Can Bestop provide custom doors with specific fire or acoustic ratings? A5: Yes, we specialize in manufacturing custom fire-rated and acoustic doors. You must clearly specify the required rating (e.g., FD30, 45-minute, STC 38dB) and the relevant testing standard. We will then manufacture the door to meet those certified specifications.

11. Conclusion with CTA

Specifying custom doors from an overseas manufacturer requires diligence and clarity. By understanding regional standards, our custom capabilities, and the critical details required in a technical brief, you can ensure your project receives doors that perfectly match your design and performance expectations.

At Bestop Door Factory, we are committed to being your reliable partner for high-quality, custom-engineered doors. Our expertise in custom door sizes specifications China, combined with our advanced manufacturing capabilities and stringent quality control, guarantees exceptional results.

Ready to discuss your next project's door requirements? Contact Bestop Door Factory today to get a quote or speak with one of our technical sales managers. Let us help you bring your architectural visions to life with precision and excellence.

See our Interior Door Materials Guide for more information on material options.