Garage Door Header Calculator — IRC-Compliant Sizing
Size a code-compliant header over a garage door opening. Covers 8, 9, 16, and 18-foot residential spans with LVL and doubled lumber options.
Enter Dimensions
Recommended: 10% for standard framing
Results
Studs Needed
15studs
Plate Pieces
2pieces
1 top plate + 1 bottom plate
Total Lineal Feet
167lin ft
Total lumber length to purchase
Wall Area
144sq ft
Editorial Standards
Each calculator is reviewed for formula accuracy, unit consistency, and alignment with current U.S. building practices before publication. We verify outputs against published engineering references and real-world project data. Learn more about our methodology.
Garage door openings are some of the largest in residential construction — 8, 9, 16, or 18 ft wide. Sizing the header correctly is critical: an undersized garage header sags visibly, cracks drywall above, and binds the garage door mechanism.
This calculator references IRC R602.7(1) for prescriptive headers. For openings 16 ft and wider, engineered LVL or steel is typically required and should be specified by a structural engineer.
How to Size a Garage Door Header
Garage Door Header Quick Reference
(Douglas Fir #2, 2-ply, supporting roof + ceiling. Step up for 2-story loads.)
- 8 ft single door: 2-2x12
- 9 ft single door: 2-2x12 or 3-2x10
- 10 ft single door: 3-2x12 or 1-3/4 inch × 11-7/8 inch LVL
- 12 ft single door: 1-3/4 inch × 14 inch LVL or W8x18 steel
- 16 ft double door: 1-3/4 inch × 14 inch LVL or W12x14 steel — engineered
- 18 ft custom door: Engineered LVL or steel only — no prescriptive option
For 2-story loads (apartment, bonus room, or storage above the garage), step up at least one ply or one size. Always verify against the current IRC and have an engineer review for non-standard conditions.
Frequently Asked Questions
What size header for a 16 ft garage door?
16 ft is at the upper limit of IRC R602.7 prescriptive tables. Common: 3-2x12 (triple 2x12), or single 5-1/4 inch × 14 inch LVL, or steel W12x14. Always verify against engineered drawings — load class matters significantly.
What size header for a 9 ft single garage door?
Per IRC R602.7(1) for typical 1-story load: 2-2x10 doubled header. For 2-story load (garage with living space above): 3-2x10 or 1-3/4 inch × 9-1/4 inch LVL.
Can I use a 2x8 header for a garage opening?
Only for very small openings (< 4 ft wide) or very light loads. 2x10 is the practical minimum for 8 ft single doors; 2x12 is more common.
What is an LVL header?
Laminated Veneer Lumber — engineered wood beams made of thin veneers glued together. LVL handles longer spans with smaller depth than solid lumber. Standard sizes: 1-3/4″ × 7-1/4″ through 1-3/4″ × 18″.
Do I need a steel beam for a 16 ft or 18 ft garage opening?
Steel W12 or LVL is typical for 16+ ft openings. Solid lumber depths required for span exceed practical depth (a 16 ft solid lumber header would be a 2x14 minimum which doesn't exist in standard stock). Engineered beam is the practical solution.
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Calculate how many studs you need for any framing job. Enter wall dimensions and spacing for an instant piece count — supports 2×4 and 2×6 at 16 or 24-inch OC.
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