Window & Door Header Calculator
Headers span window and door openings in load-bearing walls, transferring the load from above the opening to the king studs on each side. Correct header sizing is critical — an undersized header deflects, causing doors and windows to bind, and in severe cases causes structural damage. This calculator uses IRC Table R602.7 prescriptive header sizes, which determine the required doubled lumber (or LVL alternative) based on opening width, wall type (exterior/load-bearing vs. interior/partition), and number of floors above. Enter your opening width, wall type, and stories above to get the recommended header specification, LVL alternative, board length to purchase, and a material cost estimate. For openings over 12 feet or unusual loading conditions, use an engineered LVL beam sized by a structural engineer.
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How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
What size header do I need for a 6-foot opening?
For a 6-foot exterior opening on the top floor (roof load only), use doubled 2×10 headers. With one floor above, use doubled 2×12. Always check your local building code — some jurisdictions require engineered headers for openings over 4 feet.
Do interior non-load-bearing walls need headers?
Technically, non-load-bearing walls don't require engineered headers — a doubled flat 2×4 works for most interior door openings. However, many codes require at least a single 2×4 header for any opening in a partition wall for rigidity.
How much bearing does a header need on each side?
A header must bear at least 1.5 inches on each side (on the king stud and jack stud). For wider openings or heavier loads, 3 inches of bearing is recommended. The total header length = opening width + 3 inches (1.5" bearing on each side). Always buy boards at least 4 inches longer than the opening width.
Can I use a single board instead of doubled headers?
Some codes allow single LVL beams in place of doubled dimensional lumber headers — they take up less wall space and are straighter. A single 3.5"×5.5" LVL beam is often equivalent to a doubled 2×8. For 2×6 exterior walls, you'll add a 1/2" OSB spacer between two 2× boards to fill the wall depth regardless.