Window Header Size Calculator
Calculate the correct header size for window and door openings based on span width and load conditions.
Window and Door Headers are horizontal structural members that transfer the load above an opening down to the jack studs on either side. Choosing the wrong header size can lead to sagging, cracking, or structural failure.
How Header Sizing Works: The required header size depends on three main factors:
- Span width — the width of the opening
- Load condition — what is above the header (roof only, one floor, two floors)
- Building material — solid lumber, engineered lumber (LVL), or steel
Standard Header Sizes (Solid Lumber, Doubled):
| Span Width | Roof Only | One Floor Above | Two Floors Above |
|---|---|---|---|
| Up to 4 ft (1.2 m) | 2×6 | 2×6 | 2×8 |
| 4–6 ft (1.2–1.8 m) | 2×6 | 2×8 | 2×10 |
| 6–8 ft (1.8–2.4 m) | 2×8 | 2×10 | 2×12 |
| 8–10 ft (2.4–3.0 m) | 2×10 | 2×12 | LVL required |
| 10–12 ft (3.0–3.7 m) | 2×12 | LVL required | LVL required |
| Over 12 ft (3.7 m) | LVL or steel | LVL or steel | LVL or steel |
Header Construction:
- Standard headers use two pieces of dimensional lumber with 1/2" plywood spacer between them.
- This creates a header that matches the 3.5" depth of a 2×4 wall (or 5.5" for 2×6 walls).
- Example: a doubled 2×8 header = two 2×8 boards + 1/2" plywood = 3.5" total thickness.
Engineered Lumber (LVL): Laminated Veneer Lumber is significantly stronger than solid lumber. A single LVL beam can often replace a doubled solid lumber header. LVL is recommended for spans over 8–10 ft (2.4–3.0 m).
Non-Load-Bearing Walls: If the wall is non-load-bearing (does not support structure above), a flat 2×4 header is sufficient for any span width.
Practical Example: A 6-foot-wide window in an exterior wall with one floor above:
- Recommended header: doubled 2×10 (two 2×10 boards + 1/2" plywood spacer)
- Jack studs: one on each side of the opening
- Cripple studs: short studs above the header to maintain stud spacing
Tips:
- Always verify whether a wall is load-bearing before choosing a header size.
- Local building codes may differ from general guidelines. Always check with your building department.
- For garage doors and other large openings (over 10 ft / 3 m), consult a structural engineer.
- Headers in 2×6 walls need a wider spacer (two layers of 1/2" plywood or 1" foam + 1/2" plywood).
- When in doubt, size up — an oversized header is never a problem, but an undersized one is dangerous.