Door Header Size Calculator
Free door header size calculator based on IRC Table R602.7. Enter opening width, stories, and snow load to get header depth, jack studs, and cost.
Clear width of the door or window opening, measured between king studs.
Number of stories the header supports. IRC Table R602.7 covers up to 2 stories.
Ground snow load for your region. Check IRC Table R301.2(1) or your local building department.
Built-up headers are most common. LVL handles longer spans with less depth.
For estimation only. Structural work requires review by a licensed engineer. Local building codes take precedence over any calculator output.
How This Is Calculated
Header size determined by IRC Table R602.7 prescriptive lookup: input = opening width, stories supported, and ground snow load. Jack studs: 1 per side for openings up to 4 ft, 2 for 5-10 ft, 3 for 11-12 ft. Header weight estimated from lumber density (~0.37 lb/ft per nominal inch of depth for sawn softwood) or LVL density (~9.8 lb/ft for 3.5" x 9.25"). Cost estimates: sawn lumber $1.50-$3.00/ft/in, built-up $2.00-$4.00/ft/in, LVL $4.00-$7.00/ft/in (March 2026 US averages).
Source: Prescriptive header sizes from IRC (International Residential Code) Table R602.7 for buildings up to 2 stories. Allowable spans cross-referenced with NDS 2024 (National Design Specification for Wood Construction) bending and deflection criteria for sawn lumber and LVL.
6 min read
What Goes Above the Hole in a Load-Bearing Wall
Every time a framer cuts a door or window opening into a load-bearing wall, the structure above that opening needs a bridge. That bridge is the header — a horizontal beam that picks up the load from above and routes it down through jack studs on each side to the sole plate and foundation below.
The **door header size calculator** determines the required header dimensions for standard residential openings based on IRC Table R602.7 prescriptive requirements. Enter the opening width, the number of stories the header supports, the ground snow load for your region, and the header material type. The tool returns a code-compliant header depth, jack stud count, approximate weight, and material cost estimate.
Headers are one of the most frequently mis-sized elements in residential framing. Too small and the header deflects — causing drywall cracks above the door and doors that stick in their frames. Too large wastes material and reduces insulation space in exterior walls. The IRC prescriptive tables exist precisely to prevent both problems without requiring an engineering calculation for every opening in the house.
IRC Table R602.7 Header Requirements
The IRC provides prescriptive header sizes based on three variables: span, building height, and design loads. The table below summarises the most common combinations.
| Opening Width | 1 Storey, 30 psf Snow | 1 Storey, 50 psf Snow | 2 Stories, 30 psf Snow | 2 Stories, 50 psf Snow | |---|---|---|---|---| | 3 ft | 2x6 | 2x6 | 2x8 | 2x8 | | 4 ft | 2x6 | 2x8 | 2x8 | 2x10 | | 6 ft | 2x8 | 2x10 | 2x10 | 2x10 | | 8 ft | 2x10 | 2x10 | 2x12 | 2x12 | | 10 ft | 2x12 | 2x12 | 2x12 | 2x12 | | 12 ft | 2x12 | 2x12 | 2x12* | 2x12* |
*Openings at 12 ft with 2 stories above often exceed prescriptive table limits. An engineered header (LVL or steel) is typically required and must be designed by a licensed professional.
All sizes assume doubled members (two 2x pieces with a 1/2-inch plywood or OSB spacer to match the 3.5-inch wall width). Single solid 4x members of the same depth are an acceptable alternative per IRC Section R602.7.2.
How to Frame a Door Header Step by Step
1. **Lay out the rough opening.** Mark the king stud locations on the sole plate. The rough opening width equals the door width plus the two jack stud thicknesses (1.5 inches each for 2x lumber) plus 1/2 inch for shim space on each side. A 36-inch door needs a 38.5 to 39-inch rough opening.
2. **Install king studs.** These are full-height studs running from sole plate to top plate on each side of the opening. They carry the header load and anchor the jack studs. Nail them with three 16d nails at the top plate and toenail at the sole plate.
3. **Cut and assemble the header.** For built-up headers, sandwich a 1/2-inch plywood strip between two 2x members. The plywood brings the total width to 3.5 inches, matching the 2x4 wall depth. Apply construction adhesive to both faces and nail with 16d nails at 16 inches on centre, staggered top and bottom.
4. **Set jack studs and header.** Cut jack studs to the rough opening height minus the header depth. Nail each jack stud to its king stud with 10d nails at 12 inches on centre. Lift the header into position on top of the jack studs and nail through the king studs into the header ends with at least five 16d nails per side.
5. **Add cripple studs above.** If the header does not fill the full space to the top plate, install short cripple studs at 16-inch on-centre spacing between the header top and the top plate. These transfer top-plate loads to the header and provide a nailing surface for drywall.
Solid Lumber vs Built-Up vs LVL Headers
Three header types dominate residential construction, each with distinct trade-offs.
**Solid sawn lumber (4x)** uses a single piece of dimensional lumber — a 4x8, 4x10, or 4x12. The 3.5-inch actual width fills a 2x4 wall cavity exactly. Solid headers are simple to install and available at any lumberyard. The downside: sawn lumber has natural defects (knots, grain deviation, checks) that reduce its actual capacity below the published grade values. Quality varies from board to board, and it is hard to find straight, defect-free 4x material in longer lengths.
A **built-up header** pairs two 2x members with a plywood spacer. Because the framer selects the better of the two boards for the tension face (bottom), built-up headers are more reliable than solid lumber in practice. The spacer also creates an insulation cavity — a 2x10 built-up header with 1/2-inch plywood leaves a 1-inch gap that can be filled with rigid foam, reducing thermal bridging. Built-up headers are the default choice for production framing because the materials are lighter to handle individually and always in stock.
**LVL headers** use engineered lumber manufactured from thin wood veneers laminated under heat and pressure. LVL has no knots, consistent properties, and published design values 30 to 50% higher than equivalent sawn lumber. For openings over 8 feet, LVL is often the only wood option that works without increasing the header depth beyond what fits in a standard wall. The penalty: LVL costs two to three times more per foot than dimensional lumber and must be special-ordered at many yards. For a quick comparison of [window and door sizing](/calculators/materials/window-and-door-sizing-calculator) options, pair this calculator with rough-opening data from the window and door sizing tool.
Common Header Mistakes and How to Avoid Them
Even experienced framers make header errors that lead to callbacks. The following problems appear repeatedly on job sites and in home inspections.
Is a header required in every wall opening? Not always. Non-load-bearing partition walls do not require structural headers. A flat 2x4 laid on edge across the top of the opening (a "flat header") is sufficient to support the drywall and casing. Installing a structural header in a partition wall wastes material and labour. Check the framing plans — if the wall is marked "NLB" (non-load-bearing), skip the structural header.
What happens if the header is undersized? The header deflects under load, causing diagonal drywall cracks above the door corners — the classic "picture frame" crack pattern. Doors and windows bind in their frames, becoming difficult to open or close. In severe cases, the header can sag visibly, requiring removal and replacement with a correctly sized member. Fixing an undersized header after the house is drywalled and trimmed costs $1,500 to $4,000 depending on access and finish repair.
Can I use a single 2x instead of a doubled header? IRC Table R602.7 requires doubled members or a single 4x member. A single 2x does not provide adequate bending capacity for structural headers. The only exception is IRC Section R602.7.4, which permits single 2x4 flat headers for openings up to 4 feet wide in single-storey buildings with limited roof loads — a narrow exception that applies mainly to closet doors and small windows.
Do I need a header in an exterior wall above a garage door? Garage door openings in exterior walls always require headers because exterior walls are load-bearing. Garage door headers are typically the largest in the house — an 8-foot single door needs a minimum 2x10, and a 16-foot double door exceeds prescriptive table limits, requiring an engineered beam. Use the [steel beam size calculator](/calculators/structural/steel-beam-size-calculator) if your garage opening exceeds 12 feet.
Worked Examples
Example 1
Scenario: A framer needs a header for a 6-foot-wide double entry door in a two-storey home with 30 psf ground snow load. The wall is load-bearing with standard 2x4 framing.
Calculation: Opening width = 6 ft, stories above = 2, snow load = 30 psf, header type = built-up lumber. Per IRC Table R602.7 for a 6-ft span with 2 stories: required header depth is 2x10. Built-up header = two 2x10s with 1/2-inch plywood spacer. Header depth = 9.25 in (actual). Jack studs required = 2 per side. Header weight = 2 x (3.4 lb/ft x 6 ft) + spacer = approximately 42.4 lbs. Estimated material cost = $45-$75 for lumber and spacer.
What this means: A doubled 2x10 header handles a 6-foot opening with two full stories of load above. This is one of the most common header scenarios in residential construction. The two jack studs on each side transfer the header load down to the sole plate and foundation.
Takeaway: For openings up to 6 feet in standard residential framing, built-up dimensional lumber headers are the most economical choice. Budget $45-$75 in materials. The labour to cut and assemble the header takes an experienced framer about 30 minutes.
Example 2
Scenario: A contractor installs a 10-foot-wide picture window in a single-storey ranch with a 50 psf snow load region. They opt for an LVL header to minimise depth and maximise headroom.
Calculation: Opening width = 10 ft, stories above = 1, snow load = 50 psf, header type = LVL. Per IRC Table R602.7 for a 10-ft span with 1 storey and heavy snow load: required header depth is approximately 11.25 in. LVL header = 3.5-inch-wide x 11.875-inch LVL (standard size). Jack studs required = 2 per side. Header weight = approximately 9.8 lb/ft x 10 ft = 98 lbs. Estimated material cost = $120-$180 for the LVL beam.
What this means: At 10 feet wide, the opening pushes past what doubled 2x10s can span in a heavy snow region. The LVL header provides the required bending capacity at a consistent depth without the variability of sawn lumber. At 98 pounds, two workers can lift it into position without equipment.
Takeaway: LVL headers cost roughly double the price of built-up dimensional lumber but eliminate concerns about knots, splits, and crowning that weaken sawn lumber at longer spans. For openings over 8 feet, LVL is worth the premium.
Frequently Asked Questions
- What size header do I need for a 6-foot door opening?
- A 6-foot door opening in a load-bearing wall typically requires a doubled 2x8 header if supporting one storey with moderate (30 psf) snow load, or a doubled 2x10 if supporting two stories or in a heavy snow region. These sizes come from IRC Table R602.7 prescriptive requirements. The doubled members are separated by a 1/2-inch plywood spacer to match the 3.5-inch width of a 2x4 wall. Each side needs two jack studs to transfer the header load to the foundation.
- Do non-load-bearing walls need headers above doors?
- Non-load-bearing partition walls do not require structural headers. A flat 2x4 spanning the top of the opening is sufficient to support drywall and door casing. However, correctly identifying whether a wall is load-bearing is critical before making this decision. If floor joists or roof trusses bear on the wall from above, it is load-bearing and requires a full structural header per IRC Table R602.7. When in doubt, treat the wall as load-bearing or have a contractor verify the framing before proceeding.
- How many jack studs do I need for a door header?
- The IRC requires a minimum of one jack stud (also called a trimmer stud) per side for openings up to 4 feet wide, two jack studs per side for openings from 5 to 10 feet, and three per side for openings wider than 10 feet. Jack studs transfer the full header load to the sole plate and foundation. They must be continuous from the sole plate to the underside of the header — spliced or pieced-together jack studs are not permitted. Each jack stud is face-nailed to its adjacent king stud with 10d nails at 12 inches on centre.
- When should I use an LVL header instead of dimensional lumber?
- LVL (Laminated Veneer Lumber) headers make sense in three situations: openings wider than 8 feet where dimensional lumber deflects excessively, heavy-load scenarios with two stories and high snow loads where the prescriptive table pushes to 2x12 maximums, and exterior walls where the narrower LVL profile leaves room for insulation behind the header. LVL design values are 30 to 50 percent higher than equivalent-depth sawn lumber, which sometimes allows a shallower header that preserves headroom. The trade-off is cost — LVL runs two to three times the price of standard framing lumber per linear foot.
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