Inputs
Formula Used
Triangular dispersion above the opening (45° rule).
- Total masonry load per meter length: W = γ · t · (L · h / 2)
- Equivalent UDL: wm = W / L = γ · t · h / 2
- Service UDL: ws = wm + wextra
- Factored UDL: wu = ws · LF
Simply supported lintel under uniform load.
- Maximum moment: M = wu · L² / 8
- Maximum shear: V = wu · L / 2
- Section modulus: Z = M / σ
- Rectangular: Z = b · d² / 6 ⇒ d = √(6Z/b)
- Shear stress: τ = V / (b · d)
- Deflection: δ = 5 ws L⁴ / (384 E I), I = b h³ / 12
The masonry model is a quick sizing approach. For final design, apply local codes, detailing rules, and load combinations.
How to Use This Calculator
- Measure the clear span of the opening in meters.
- Enter the wall thickness and masonry height above the opening.
- Provide unit weight and any extra uniform loads.
- Set bearing length, allowable stresses, and a load factor.
- Press Calculate to view moment, shear, and suggested depth.
- Review shear, deflection, and bearing flags before deciding.
- Export CSV or PDF to keep a project record.
Example Data Table
| Case | Span (m) | Thickness (mm) | Height (m) | Extra UDL (kN/m) | Load Factor | Suggested Depth (mm) |
|---|---|---|---|---|---|---|
| A | 1.20 | 115 | 0.45 | 2.0 | 1.50 | 150 |
| B | 1.80 | 230 | 0.60 | 3.0 | 1.50 | 190 |
| C | 2.40 | 230 | 0.75 | 4.5 | 1.50 | 235 |
| D | 3.00 | 300 | 0.90 | 6.0 | 1.50 | 290 |
The table shows typical ranges; your project values may differ.
Professional Article
1) Why lintel sizing matters
Lintels bridge door and window openings and carry masonry plus any superimposed loads. If a lintel is undersized, the wall can crack above corners, finishes can distort, and doors may bind. This tool supports early sizing by estimating bending, shear, and deflection for a simply supported member.
2) Typical input ranges seen on site
Many residential openings fall between 0.9 and 2.4 m; wider garage spans may reach about 3.0 m. Wall thickness commonly includes 115, 150, 200, 230, and 300 mm. Masonry unit weight is often near 18–22 kN/m³, while bearing lengths frequently range from 100 to 200 mm depending on block strength and workmanship.
3) Load model used in the calculator
A practical sizing method assumes load spreads at roughly 45° above the opening, producing a triangular wedge of masonry. The equivalent masonry line load is wm = γ · t · h / 2. Add extra line load to represent roof or floor reactions that frame into the wall above the opening.
4) How span increases demand
Under a uniform load, maximum moment is M = w · L² / 8, so span has a strong effect. If span doubles and load stays similar, moment rises by about four times. Maximum shear is V = w · L / 2, which often controls near supports when bearing is limited.
5) Translating moment into depth
The tool computes required section modulus using Z = M / σ. For a rectangular member, Z = b · d² / 6, giving d = √(6Z/b). Breadth is commonly aligned with the wall thickness for full bearing and consistent finishes.
6) Shear, bearing, and deflection checks
Shear stress is screened with τ = V / (b · d). Bearing stress is estimated from reaction divided by t · bearing. Deflection is an elastic estimate compared to a service limit such as L/360. If deflection is high, increasing depth is usually the most efficient improvement.
7) Practical detailing notes
Ensure adequate bearing, level seating, and straight alignment. Cover allowance influences overall depth for durability. If masonry is weak or poorly bonded, increase bearing length, use padstones, or select a different lintel system. Temporary propping during construction can reduce early cracking risk.
8) Using results for coordination
Use these outputs for preliminary comparison, then verify with local standards, confirmed material properties, and final load combinations. Exported reports help communicate assumptions, track revisions, and respond quickly to site questions.
FAQs
1) What should I enter as extra uniform load?
Include loads from floors, roofs, or façade framing that bears on the wall above the opening. Convert point loads into an equivalent line load for early sizing, then confirm with final framing drawings.
2) Is it correct to use wall thickness as lintel width?
It is a common assumption for masonry walls because it supports full bearing and consistent finishes. If you use a narrower lintel, confirm bearing, eccentricity, and any required packing or ties.
3) How much bearing length is usually needed?
Many projects use 100–200 mm per end, but required bearing depends on masonry strength and workmanship. If bearing stress is high, increase bearing length, use padstones, or change the lintel type.
4) How do I choose allowable bending and shear stresses?
Use values consistent with your design approach and material. For early checks, choose conservative limits. Final design should follow the applicable standard and verified material test data.
5) Why is the deflection check optional?
Deflection depends strongly on stiffness assumptions and cracking behavior in reinforced members. The calculator provides an elastic estimate for screening. Always verify serviceability using the rules in your local standard.
6) Can the tool be used for steel or precast lintels?
Yes for preliminary sizing because the action effects are general. However, section properties, connection details, and deflection limits differ by system. Use the computed moment and shear as inputs to your detailed member design.
7) What if my opening span is large or heavily loaded?
For large spans, consider engineered beams, composite solutions, or intermediate supports. Increase depth, check bearing carefully, and confirm lateral stability. Engage a qualified structural engineer for final verification and detailing.
Build safer openings by sizing lintels with confidence today.