Math & Engineering
Door Header Size Calculator
Calculate the required door header size for your door opening based on width, wall load, and span.
Reviewed by the calculator.uk.com Team · Last reviewed 13 July 2026 · Our methodology
Enter values to calculate the required door header size
Related to Door Header Size Calculator
The Door Header Size Calculator determines the appropriate size of a door header (also known as a lintel or beam) based on several key factors that affect the structural load. The calculator takes into account the door width, wall load type, floor span above the door, and roof span to recommend a suitable header size that will safely support the weight above the door opening.
Load Calculations
The calculator considers both dead loads (permanent weight) and live loads (variable weight) in its calculations. Roof loads are typically calculated at 40 pounds per square foot (psf), while floor loads are estimated at 50 psf. The wall load type (light, medium, or heavy) applies a multiplier to account for different wall construction materials and their weights.
Size Determination
Header sizes are determined based on the total calculated load and the width of the door opening. The calculator uses standard lumber dimensions (2x6, 2x8, 2x10, 2x12) and may recommend doubled headers (2)2x12 for larger loads. For very large openings or heavy loads, an engineered beam may be recommended.
The calculator provides a recommended header size based on your input parameters. The results should be interpreted with consideration for local building codes and specific construction requirements. Here's how to understand the different components of the results:
Header Size Format
Results are shown in standard lumber dimensions (e.g., 2x6, 2x8). The first number (2) represents the thickness in inches, while the second number (6, 8, etc.) represents the height in inches. When you see (2) before the size, it indicates that two pieces of lumber should be used together.
Engineered Beam Recommendation
If you see "Engineered beam required" in the results, this means the load or span is too large for standard lumber headers. In these cases, you should consult a structural engineer to specify an appropriate engineered beam solution.
1. What is a door header?
A door header is a horizontal structural beam that spans the top of a door opening and supports the weight of the wall, floor, and/or roof above. It's a crucial structural element that prevents the weight above the door from causing the opening to sag or collapse.
2. Why does wall load type matter?
The wall load type (light, medium, or heavy) significantly affects the total weight the header must support. Light walls typically represent interior, non-load bearing walls, medium walls are usually exterior walls, and heavy walls indicate masonry or concrete construction, each requiring different header sizes to safely support the load.
3. When should I use doubled headers?
Doubled headers (indicated as (2)2x12, for example) are recommended when a single header would be insufficient to support the load. This typically occurs with wider door openings or when there are significant loads from floors or roofs above the door.
4. Do I need to consider local building codes?
Yes, always consult your local building codes and obtain necessary permits before construction. While this calculator provides general guidance, local codes may have specific requirements for header sizes, materials, and installation methods that must be followed.
5. What is the scientific source for this calculator?
This tool uses a simplified load-and-span heuristic rather than a full engineered header table lookup: it sums an assumed roof load of 40 psf and floor load of 50 psf over your entered spans, scales the total by a wall-weight multiplier, then steps up through standard lumber sizes as that load increases. Those psf figures are common conservative assumptions for light residential wood-frame construction, but the sizing breakpoints are simplified for quick estimating and are not a substitute for the header span tables in the International Residential Code or a stamped calculation from a structural engineer. Always confirm the final header size against your local code before building.