Lintel Header Size Calculator
Plan your structural engineering project with our free lintel header size calculator. Get precise measurements, material lists, and budgets.
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Formula
The header is modeled as a simply supported beam carrying a uniform load equal to the total tributary dead and live loads from above. The bending moment is wL-squared over 8. The required section modulus S is the moment divided by the allowable bending stress. The header must also satisfy the deflection limit of L/360 to prevent cracking in finishes above the opening.
Last reviewed: December 2025
Worked Examples
Example 1: 6-Foot Window in One-Story Wall
Example 2: 8-Foot Door in Two-Story Wall
Background & Theory
The Lintel Header Size Calculator applies the following established principles and formulas. Structural and construction engineering is governed by fundamental load analysis, material science, and regulatory standards that ensure the safety and durability of built structures. The primary distinction in load analysis is between dead loads โ the permanent self-weight of structural elements, finishes, and fixed equipment โ and live loads, which represent variable occupancy, furniture, and environmental forces such as wind and snow. These are combined using factored load equations, such as the ASCE 7 formula U = 1.2D + 1.6L, where D is dead load and L is live load. Concrete mix design is governed by the water-cement (w/c) ratio, which is the primary determinant of compressive strength and durability. A w/c ratio of 0.40โ0.45 typically yields concrete with 28-day compressive strengths of 30โ40 MPa. Common mix ratios by weight for structural concrete are approximately 1 part cement : 1.5โ2 parts sand : 3 parts coarse aggregate. Structural steel is characterized by its yield strength (the stress at which permanent deformation begins, typically 250โ350 MPa for mild steel) and ultimate tensile strength (typically 400โ500 MPa). Mid-span deflection of a simply supported beam under a central point load is given by ฮด = FLยณ / (48EI), where F is force, L is span length, E is Young's modulus, and I is the second moment of area. Building insulation is rated by R-value, a measure of thermal resistance in units of mยฒยทK/W (SI) or ftยฒยทยฐFยทh/BTU (imperial). Higher R-values indicate greater resistance to heat flow. Foundation design depends on the allowable bearing capacity of the underlying soil, which ranges from approximately 75 kPa for soft clay to over 10,000 kPa for bedrock. Drainage gradients for surface water are typically specified as a minimum of 1โ2% slope away from building foundations to prevent hydrostatic pressure and water infiltration.
History
The history behind the Lintel Header Size Calculator traces back through the following developments. The history of construction engineering spans thousands of years of accumulated empirical knowledge and, more recently, rigorous scientific analysis. The ancient Egyptians built the Great Pyramid of Giza around 2560 BCE using an estimated 2.3 million stone blocks, demonstrating sophisticated logistics, geometry, and workforce organization. Roman engineers advanced the field dramatically through the use of pozzolanic concrete โ a mixture of volcanic ash, lime, and seawater โ enabling the construction of the Pantheon dome (43.3 m diameter, completed around 125 CE) and a vast network of aqueducts and roads across the empire. Cast iron emerged as a structural material during the Industrial Revolution, first used prominently in the Iron Bridge at Coalbrookdale, England, completed in 1779. Wrought iron and later steel allowed far greater spans and heights. The Eiffel Tower, completed in 1889, demonstrated the structural possibilities of wrought iron at scale and influenced the development of steel-frame skyscraper construction in Chicago and New York. Reinforced concrete was systematically developed by Joseph Monier, a French gardener, who patented iron-reinforced concrete pots and panels in the 1860s, and later by engineers including Franรงois Hennebique who created the first comprehensive reinforced concrete framing system in the 1890s. The 1906 San Francisco earthquake caused widespread devastation and galvanized the engineering profession to develop seismic design provisions. Subsequent earthquakes โ including the 1971 San Fernando and 1994 Northridge events โ drove successive improvements in seismic codes, base isolation technology, and ductile detailing of reinforced concrete and steel frames. Building codes became increasingly standardized in the twentieth century, with the International Building Code (IBC) first published in 2000 providing a unified model code adopted across much of the United States. Building Information Modeling (BIM) emerged in the 2000s as a digital workflow integrating architectural, structural, and MEP design into a unified three-dimensional model, fundamentally changing coordination practices across the industry.
Frequently Asked Questions
Formula
M = wL2/8 | Required S = M/Fb | Check delta <= L/360
The header is modeled as a simply supported beam carrying a uniform load equal to the total tributary dead and live loads from above. The bending moment is wL-squared over 8. The required section modulus S is the moment divided by the allowable bending stress. The header must also satisfy the deflection limit of L/360 to prevent cracking in finishes above the opening.
Worked Examples
Example 1: 6-Foot Window in One-Story Wall
Problem: Determine the header size for a 6-foot window opening in a one-story exterior bearing wall with 30 psf total roof load.
Solution: Roof tributary = 6 ft, Wall DL = 7 * 8 = 56 plf\nTotal = 30 * 6 + 56 = 236 plf\nSpan = 6.25 ft, M = 236 * 6.25^2 / 8 = 1,152 ft-lb\nRequired S = 1152 * 12 / 1200 = 11.52 in3\n2-2x8 has S = 26.28 -> PASS
Result: Recommended: 2-2x8 header
Example 2: 8-Foot Door in Two-Story Wall
Problem: Size a header for an 8-foot garage door opening with two stories of load above.
Solution: Floor load = 50 * 6 = 300, Roof = 30 * 6 = 180, Wall = 56 * 2 = 112\nTotal = 592 plf, Span = 8.25 ft\nM = 592 * 8.25^2 / 8 = 5,036 ft-lb\nRequired S = 5036 * 12 / 1200 = 50.36 in3\n3-2x10 has S = 64.17 -> PASS
Result: Recommended: 3-2x10 header
Frequently Asked Questions
How do I determine the correct header size for a window or door opening?
Header size depends on the opening width, the loads being supported, and the lumber grade. For one-story exterior walls with standard roof loads, a doubled 2x8 header typically handles openings up to 6 feet, while a doubled 2x10 can span up to 8 feet. For two-story loads or wider openings, doubled 2x12 or triple-ply headers may be needed. The key is to calculate the total load per linear foot on the header, then check that both the bending stress and deflection are within allowable limits.
What loads does a header carry?
A header carries all loads from above the opening down to the jack studs at each side. For a bearing wall, this includes the roof dead and live loads, any floor loads from stories above, and the weight of the wall framing itself. The tributary width of the roof or floor load is typically half the joist span on each side. For a non-bearing interior wall, the header only carries the weight of the wall framing and any finishes above the opening, which is much lighter.
What is the difference between a lintel and a header?
In wood-frame construction, a header is a horizontal structural member placed above a window or door opening in a wall to transfer loads around the opening to the jack studs. A lintel serves the same purpose but is more commonly used in masonry construction, where it spans across the top of an opening in a brick or block wall. In practice, the terms are often used interchangeably in residential construction. Steel lintels or angle iron are common in masonry, while wood or engineered lumber headers are standard in framed walls.
How do I size an HVAC system for a building?
HVAC sizing uses Manual J calculations considering square footage, insulation, window area, climate zone, and occupancy. A rough estimate is 1 ton of cooling per 400-600 square feet. Oversized systems short-cycle and waste energy; undersized systems cannot maintain comfort.
Why might my result differ from another tool or reference?
Differences typically arise from rounding conventions, the specific version of a formula (for example, simple vs compound interest), or unit inconsistencies between inputs. Check that both tools are using the same formula variant and the same units. The References section links to the authoritative source behind the formula used here.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
References
Reviewed by Abdullah, Technical Content Specialist ยท Editorial policy