Door Header Size Calculator
ConstructionEstimate the required header depth for a door or window opening based on span width and load condition. Quick rule-of-thumb sizing for framing projects.
Required Header Depth
6
Opening Width
6
What is a Header Size?
A Door Header Size Calculator estimates the required header depth for a door or window opening using a simplified rule-of-thumb span factor based on opening width and load condition. It gives you a quick approximation — roughly one inch of header depth per foot of span for a load-bearing single-story wall — to use for early planning before consulting an official span table or structural engineer.
This is not a substitute for a full engineered span table. Building codes publish detailed prescriptive tables (and often require engineering for wider spans or heavier loads) that account for lumber species, grade, snow load, and more. Pair this tool with the Floor Joist Calculator when planning an entire framing project.
How to use this Header Size calculator
- Enter the Opening Width in feet — the horizontal distance the header must span.
- Select the Load Condition — non-load-bearing wall, load-bearing with a single story above, or load-bearing with two stories above.
- Review the Required Header Depth result in inches.
- Round the result up to the nearest standard built-up header size (2×6, 2×8, 2×10, or 2×12).
- Verify your final header size against your local building code's official span tables, or consult a structural engineer, especially for any load-bearing wall.
Formula & Methodology
The calculator applies a simplified rule-of-thumb span factor: Required Header Depth (in) = Opening Width (ft) × Load Factor × 1.0 Where the Load Factor is 0.5 for a non-load-bearing wall, 1.0 for a load-bearing wall with a single story above, and 1.3 for a load-bearing wall with two stories above. Worked example: For a 6 ft opening in a load-bearing wall with a single story above: Required Header Depth = 6 × 1.0 × 1.0 = 6.0 in, which rounds up to a standard 2×8 (7.25 in) built-up header. This is a rule-of-thumb estimate only — always verify against your local building code's official span tables or consult a structural engineer before finalizing a load-bearing header size.
Frequently Asked Questions
A door header (also called a lintel) is a horizontal structural member installed above a door or window opening to carry the load from above and transfer it down to the wall studs on either side of the opening. Headers are typically built up from two or more pieces of dimensional lumber sandwiched together, sized according to the width of the opening and how much weight the wall above must support.
Header depth refers to the vertical dimension of the lumber used (for example, a 2×10 has a depth of 9.25 inches), while the header's length spans horizontally across the opening plus bearing on each side. This calculator estimates the required depth — the dimension that determines how much load the header can carry — not the total length of lumber needed.
Yes, most building codes still require a header in non-load-bearing walls to provide a solid nailing surface and maintain wall alignment, but it can typically be shallower since it isn't carrying structural weight from above. This calculator applies a reduced load factor of 0.5 for non-load-bearing openings to reflect that lighter requirement.
Each additional story above an opening adds more dead load (structure weight) and live load (occupants, furniture, snow) that the header must transfer around the opening, so headers supporting two stories need significantly more depth than those supporting a single story. This calculator applies a higher load factor for two-story conditions to reflect that increased demand.
Standard built-up header depths correspond to common dimensional lumber sizes: a 2×6 measures 5.5 inches deep, a 2×8 measures 7.25 inches, a 2×10 measures 9.25 inches, and a 2×12 measures 11.25 inches. Always round your calculated result up to the next standard size, since headers are typically built from doubled or tripled dimensional lumber rather than custom-milled depths.
No, this is a simplified rule-of-thumb estimate intended for early planning and rough budgeting, not a substitute for an engineered header size table or a structural engineer's calculation. Local building codes publish official prescriptive span tables (or require engineering) for load-bearing headers, and you should always verify against those tables or consult a licensed professional before finalizing framing plans.
Real header sizing accounts for roof and floor load (live and dead loads), the number of stories supported, snow load in your region, the species and grade of lumber, and whether point loads from trusses or beams land directly above the opening. This calculator simplifies all of that into a single load factor, so it should only be used as a starting point.
A header specifically spans a door or window opening within a wall, while a beam is a more general structural term for any horizontal load-carrying member, which could span a much larger area such as an entire room. Headers are essentially short-span beams sized for the specific width of a wall opening.
This calculator can give a rough starting estimate for a garage door opening, but garage door headers typically span much wider openings (8 to 16+ feet) and carry significant roof load, so they almost always require an engineered beam calculation rather than a simplified rule of thumb. Consult a structural engineer or your local building department for garage door header sizing.
A wall is generally load-bearing if it runs perpendicular to floor or ceiling joists above, sits along the centerline of the house, or has framing members (like posts or other walls) stacked above it on upper floors — but the only reliable way to confirm is by reviewing your home's structural plans or having a professional inspect the framing. When in doubt, treat the wall as load-bearing for safety.
Header sizing and floor joist sizing both start from the same basic principle — longer spans and heavier loads require deeper structural members — but they use different span tables since joists and headers carry loads differently. See the [Floor Joist Calculator](/floor-joist-calculator/) for estimating joist spans in the same framing project.
Use this estimate to get a rough sense of lumber requirements for budgeting and planning purposes, then confirm the actual required size using your local building code's prescriptive header span table or by consulting a structural engineer, especially for any load-bearing wall. Also check with your local building department about permit requirements before starting the project.
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