Door Header Size Calculator
Enter your rough opening to instantly find a recommended door header size — quick for DIYers, accurate enough for pros.
Calculation Assumptions
- Lumber species: SPF #2
- Bearing length: 1.5 inches
- Frost loads ignored
- Conservative uniform load values used
How this result was calculated
Clear span = 36″ – 0.75″ = 35.25″
Based on span tables for SPF #2 lumber with no additional loads
Recommended header size: 2-ply 2×8
How this calculator works
This calculator determines the appropriate door header size based on your specific opening dimensions and load conditions. It uses standardized span tables and engineering principles to provide safe recommendations for residential construction.
What header size do I need for a 36 inch opening?
For a typical 36-inch rough opening under light loading conditions:
- Calculate clear span: 36″ – 0.75″ = 35.25″
- Check span table for appropriate header size
- For SPF #2 lumber with no additional loads: 2-ply 2×6 or single 2×8
- Verify bearing length requirements (minimum 1.5 inches)
Always confirm with local building codes and consult an engineer for unusual conditions.
Quick mode — find header size
Quick mode provides instant header size recommendations based on standard residential construction assumptions. Simply enter your rough opening width, and the calculator will determine the appropriate header size using conservative defaults.
This mode is ideal for typical interior door openings in single-story construction where no significant additional loads are present.
Advanced mode — include roof or second floor loads
Advanced mode allows you to specify additional parameters that affect header sizing:
- Material type: Choose between different lumber species or engineered wood products
- Load conditions: Account for roof loads, second floor loads, or combined loads
- Bearing length: Adjust based on your specific wall construction
- Regional standards: Select between US imperial or metric measurements
Use this mode for exterior walls, load-bearing partitions, or when supporting additional structural elements.
Header span table
The following table provides conservative header size recommendations based on clear span and loading conditions for SPF #2 lumber:
| Clear Span (inches) | No Additional Load | Roof Load Only | Second Floor Load |
|---|---|---|---|
| Up to 36″ | 2×6 (1-ply) | 2×6 (1-ply) | 2×8 (1-ply) |
| 37″ – 60″ | 2×8 (1-ply) | 2×8 (1-ply) | 2×10 (1-ply) |
| 61″ – 84″ | 2×10 (1-ply) | 2×10 (2-ply) | 2×12 (2-ply) |
| 85″ – 108″ | 2×12 (2-ply) | 2×12 (2-ply) | Engineered Solution |
| Over 108″ | Engineered Solution | Engineered Solution | Engineered Solution |
If your required header exceeds 12 ft, this tool will recommend consulting a structural engineer.
Frequently asked questions
Rough opening is the framed opening size, typically 2 inches wider and 2 inches taller than the door unit. Clear span is the actual distance between supports that the header must bridge, which is typically 0.75-1 inch less than the rough opening width to account for framing gaps.
LVL (Laminated Veneer Lumber) headers are recommended when:
- Span exceeds what dimensional lumber can safely support
- Higher load capacity is needed in a smaller space
- Consistent, predictable performance is required
- Supporting heavy loads like multiple stories or roof loads
Different load types significantly impact header requirements:
- No additional load: Interior non-load-bearing walls
- Roof load only: Exterior walls supporting roof only
- Second floor load: Walls supporting a second floor
- Roof + second floor: Walls supporting both roof and additional floors
Heavier loads require larger or multiple-ply headers.
This calculator uses conservative assumptions suitable for most residential applications. If your project involves unusual conditions, heavy loads, or complex structural requirements, consult a qualified structural engineer. Building codes vary by location, so always verify with local requirements.
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