Door Header Size Calculator: Beam Span and Lumber Sizing
Enter your rough opening width, wall type, and load condition to get the recommended door header size based on prescriptive IRC R602.7 tables. You also get the jack stud count per side, the actual header depth in inches, and whether an engineered beam is required. Switch to the reverse mode to find the maximum safe span for a header you already have on hand.
What is a door header and why does size matter?
A door header (also called a lintel) is the horizontal structural member spanning the top of a rough opening. It carries the load from the wall framing, floor, and roof above and transfers it to the trimmer studs and king studs on either side of the opening. An undersized header can sag, crack the surrounding drywall, or cause the door to rack and stick. An oversized header wastes lumber and, in an exterior wall, reduces room for insulation. Getting the size right is a balance of safety, code compliance, and cost efficiency.
How door header size is determined
Two methods are used in practice. The first is the prescriptive method from IRC Table R602.7: look up your rough opening width and load condition in a span table, and read off the minimum doubled-lumber size. No engineering calculations are needed. The second is the engineered method, which uses structural calculations for spans over 12 feet, unusual loads, or engineered lumber such as LVL (laminated veneer lumber) or PSL. For most residential doors - interior or exterior - the prescriptive table is sufficient and is what this calculator uses. The three key variables are: (1) span, the clear width of the rough opening; (2) load condition, whether the wall carries a floor, roof, or is simply a non-load-bearing partition; and (3) lumber species and grade, with Spruce-Pine-Fir or Douglas Fir-Larch No. 2 being the standard assumption in most IRC tables.
Jack studs, king studs, and cripple studs
Framing a door opening involves three types of studs working together. Jack studs (also called trimmer studs) run from the sole plate to the underside of the header and carry the header load vertically. The number of jack studs per side increases with span: one is enough for openings under roughly 6 feet, two for larger spans. King studs are full-height studs on the outside of each jack stud that pin the assembly to the top and bottom plates. Cripple studs fill the short gap between the header and the top plate, transferring wall loads above the opening down to the header. For non-load-bearing interior walls, the code allows a doubled flat 2x4 header with cripples, or even a single piece in some jurisdictions - but when in doubt, treat the wall as load-bearing.
When to call a structural engineer
Prescriptive tables cover most residential door openings up to about 12 feet. Beyond that, or if you are opening up a wall that carries an unusual load (such as a point load from a ridge beam, a heavy masonry chimney, or multiple floors of weight), an engineer is required. Engineered lumber options include LVL (laminated veneer lumber, typically 1.75 inches wide), PSL (parallel strand lumber), and glulam beams. These allow longer spans in a shallower depth, which is valuable when headroom above the opening is limited. Steel lintels are common in masonry construction and some commercial applications. Always check whether your local jurisdiction has amendments to the IRC that affect header requirements, especially in high-wind or seismic zones.
Quick-reference header sizing by span and load (IRC R602.7)
| Rough opening | Non-load-bearing | Roof and ceiling only | One floor + roof | Jack studs/side |
|---|---|---|---|---|
| Up to 3 ft 6 in | 2x4 doubled | 2x4 or 2x6 doubled | 2x6 doubled | 1 |
| 3 ft 6 in - 5 ft | 2x4 doubled | 2x6 doubled | 2x8 doubled | 1 |
| 5 ft - 6 ft 6 in | 2x4 doubled | 2x8 doubled | 2x10 doubled | 1-2 |
| 6 ft 6 in - 8 ft | 2x6 doubled | 2x10 doubled | 2x12 doubled | 2 |
| 8 ft - 10 ft | 2x6 doubled | 2x12 doubled | 3-ply 2x12 | 2 |
| 10 ft - 12 ft | 2x8 doubled | 3-ply 2x12 | LVL required | 2-3 |
| Over 12 ft | Engineer required | Engineer required | Engineer required | 3+ |
Based on prescriptive IRC Table R602.7 for Spruce-Pine-Fir or Douglas Fir-Larch No. 2 in standard residential construction. Verify with local code before building.
Frequently asked questions
What size header do I need for a 36-inch (3-foot) door?
A standard 36-inch pre-hung door has a rough opening of about 38-39 inches (roughly 3 ft 3 in). In a load-bearing wall carrying roof and ceiling only, a doubled 2x6 is typically sufficient at that span. For a wall carrying a floor above, step up to a doubled 2x8. In a non-load-bearing interior partition, a flat doubled 2x4 or even a single 2x4 on edge is usually acceptable per IRC. Always confirm with local code.
What size header do I need for a 6-foot opening?
A 6-foot rough opening in a load-bearing wall supporting roof and ceiling only typically calls for a doubled 2x10 per IRC prescriptive tables. If the wall also carries a floor above, move up to a doubled 2x12. For a non-load-bearing wall, a doubled 2x6 is commonly sufficient. Install two jack studs per side for any opening over about 5 feet.
What is the rule of thumb for header sizing?
The trade rule of thumb is: maximum span in inches equals the header depth in inches times 12. So a doubled 2x8 (actual depth 7.25 inches) can span up to about 87 inches (7 ft 3 in) under typical loads. This rule is a useful sanity check but is conservative for some conditions and insufficient for heavy loads; always cross-check against the applicable IRC span table for your load condition and lumber species.
Do I need a header in a non-load-bearing wall?
Yes, but a much smaller one. Even in a non-load-bearing interior partition, a header is required above every door opening to support the cripple studs and any loads from the wall itself. IRC allows a flat 2x4 header (or even a single 2x4 in some cases) for non-load-bearing walls. Some contractors use a doubled flat 2x4 for consistency regardless of whether the wall is bearing.
Can I use LVL lumber for any door header?
Yes, LVL (laminated veneer lumber) can be used for any header and is often preferred for large openings because it spans farther in a shallower depth than solid sawn lumber. Standard LVL headers are 1.75 inches wide and come in depths from 3.5 to 18 inches or more. For openings under 8-10 feet, doubled dimensional lumber is usually more economical; for longer spans or tight headroom, LVL is the practical choice. All LVL headers require a manufacturer span table or engineering calculation.
How do I measure a rough opening for a door header?
The rough opening width is the inside-to-inside distance between the trimmer studs after they are installed - not the finished door width. A pre-hung door typically needs a rough opening 2 inches wider than the door slab (for a 32-inch door, the rough opening is about 34 inches). Add 3/4 inch on each side for shimming if framing before the door is on hand. Always confirm the rough opening requirements printed on the door unit or manufacturer specifications.