Door Header Size Calculator
Calculate proper lumber header sizes for door and window openings
Calculate Door Header Requirements
The width of the opening between wall studs (includes door frame)
Standard Interior Door (30-36") (Load Factor: 1×)
Normal Load (Typical residential) (Load Factor: 1×)
Recommended Header Size
⚠️ Structural Safety Warning
• This calculator provides estimates for typical residential applications
• Always consult a licensed structural engineer for load-bearing modifications
• Follow local building codes and obtain proper permits
• Consider additional factors: lumber grade, moisture content, deflection limits
• Account for dynamic loads, seismic requirements, and environmental conditions
• Undersized headers can cause catastrophic structural failure
Example Calculation: Standard Door Header
Project Specifications
Application: Standard interior door opening
Rough Opening: 36 inches (3 feet)
Door Type: Standard interior door
Load Condition: Normal residential load
Wall: Non-load-bearing interior wall
Header Calculation
• Required Height = Opening ÷ 12 = 36" ÷ 12 = 3"
• Load Factors: Door (1.0×) × Condition (1.0×) = 1.0×
• Adjusted Requirement = 3" × 1.0 = 3"
• Minimum Header: 4" × 4" (next size up from 3")
Result: Use 4" × 4" header or built-up 2" × 4"
Standard Header Sizes
Maximum Spans (inches)
Header Construction
Built-up Headers
Two 2x boards with ½" spacer, nailed together
Solid Headers
Single piece 4x or 6x lumber, stronger per size
Engineered Headers
LVL, PSL, or steel beams for long spans
Installation
Supported by jack studs, minimum 1.5" bearing
Load Factors
Understanding Door Header Sizing
What are Door Headers?
Door headers are horizontal structural members installed above door and window openings to carry loads from above and transfer them to the surrounding wall studs. They prevent sagging and structural failure of the wall system.
Basic Sizing Rule
- •Header height = Span ÷ 12 (rule of thumb)
- •Round up to nearest standard lumber size
- •Apply load factors for safety margins
- •Consider deflection limits and code requirements
Header Sizing Formula
Required Height = (Span × Door Factor × Load Factor) ÷ 12
- Span: Rough opening width in inches
- Door Factor: Type-specific load multiplier
- Load Factor: Structural condition multiplier
- ÷ 12: Standard span-to-depth ratio
Critical Considerations
Lumber Grade
Use structural grade lumber (Douglas Fir #2 minimum) for headers.
Support Requirements
Headers must bear on jack studs with minimum 1.5" bearing length.
Code Compliance
Follow IRC/IBC requirements and local building codes for your area.