Calculator Form
Example Data Table
| Opening | Tributary Width | Total Area Load | Wall Line Load | Point Load | Material | Actual Width | Actual Depth |
|---|---|---|---|---|---|---|---|
| 3.00 ft | 6.00 ft | 55 psf | 80 plf | 0 lb | SPF Lumber | 3.00 in | 7.25 in |
| 4.00 ft | 8.00 ft | 60 psf | 100 plf | 500 lb | LVL Engineered Wood | 3.50 in | 9.25 in |
| 6.00 ft | 10.00 ft | 70 psf | 120 plf | 900 lb | Rectangular Steel Section | 4.00 in | 8.00 in |
Formula Used
Uniform line load: w = tributary width × area load + wall line load
Maximum moment: M = wL² / 8 + PL / 4
Maximum shear: V = wL / 2 + P / 2
Required section modulus: S = M × safety factor / Fb
Rectangular section modulus: S = b d² / 6
Moment of inertia: I = b d³ / 12
Deflection: Δ = 5wL⁴ / 384EI + PL³ / 48EI
Allowable deflection: Δallow = L / deflection limit
How to Use This Calculator
Enter the clear door opening span in feet. Add the tributary width carried by the header.
Enter dead, live, and roof or snow loads. Add wall line load when wall weight is known separately.
Add a point load when a beam or concentrated member lands near the center of the header.
Select a material preset or enter custom stress values. Use actual member dimensions, not nominal sizes.
Press the calculate button. Review bending, shear, deflection, and the recommended common depth.
Door Header Size Physics Guide
Why Header Size Matters
Door header sizing is a simple beam problem. The header carries loads around the opening. A door removes studs that would normally transfer weight downward. The header bridges that gap and sends the load to jack studs on both sides.
Load Path
This calculator treats the header as a simply supported beam. It estimates uniform load from tributary width and area loads. It also adds an optional point load at mid span. That point load is useful when a roof beam, floor beam, or concentrated framing member lands above the opening.
Main Structural Checks
The main checks are bending, shear, and deflection. Bending checks whether the header has enough section modulus. Shear checks stress near the supports. Deflection checks how much the header may sag under service load. A header can pass bending and still feel too flexible. That is why deflection is shown separately.
Actual Dimensions
Use actual member dimensions, not nominal names. A 2x8 is usually about 1.5 by 7.25 inches. Double members should use the combined width. For example, two 2x8 pieces act like about 3 inches wide when fastened together correctly.
Practical Limits
The result is only a preliminary physics estimate. Real building design also depends on code rules, bearing length, fasteners, cripple studs, moisture, load duration, species, grades, and lateral restraint. Engineered wood and steel members often need manufacturer tables. Local snow, wind, and seismic loads can also control the final design.
Better Planning
For safer planning, enter conservative loads first. Then compare the calculated required depth with standard sizes. If the utilization is high, choose a deeper header, wider built-up header, stronger material, or an engineered product. If deflection fails, depth usually helps more than width because moment of inertia grows with the cube of depth.
Final Review
Always confirm final framing with a qualified professional when the wall is load bearing. This is especially important for exterior walls, multi-story buildings, masonry, heavy roofs, unusual spans, or remodels where existing loads are unclear. A careful check before cutting studs can prevent sagging doors, cracked finishes, and unsafe load paths.
The calculator also reports load per linear foot. This helps compare different framing cases. Small input changes can matter. Try several scenarios before buying materials or planning inspections. Keep notes with each downloaded report for reference.
FAQs
1. What is a door header?
A door header is a horizontal beam above a door opening. It carries wall, floor, roof, or other loads around the opening and transfers them to side supports.
2. Can I use nominal lumber size?
No. Use actual dimensions for calculation. A nominal 2x8 is usually about 1.5 inches by 7.25 inches. Built-up headers need combined actual width.
3. What does tributary width mean?
Tributary width is the width of floor, roof, or wall area that sends load to the header. Larger tributary width creates higher line load.
4. Why is deflection checked?
Deflection shows estimated sag. A member may resist bending but still sag too much. Excess sag can affect doors, finishes, and appearance.
5. What is section modulus?
Section modulus measures bending strength for a cross section. A larger value means the member can resist more bending moment under the same stress limit.
6. Does this replace building code tables?
No. This tool gives a preliminary physics estimate. Code tables, manufacturer span charts, local loads, and professional review may still be required.
7. Why does depth help so much?
Depth increases section modulus and moment of inertia strongly. This is why a deeper header often improves bending and deflection more than extra width.
8. When should I contact an engineer?
Contact an engineer for load-bearing walls, large openings, heavy roofs, multi-story loads, masonry, steel work, unusual framing, or unclear existing conditions.