Calculate recommended concrete lintel size (4×8 to 12×8), design load, factored moment, shear capacity, maximum allowable deflection, bearing length, rebar schedule, and lintel weight — aligned with 2026 USA ACI 318, Oberfields lintel design guide, and TMS 402 masonry standards for CMU and brick wall openings.
A concrete lintel is a precast or cast-in-place reinforced concrete beam installed horizontally above a door, window, garage door, or any other opening in a CMU or brick masonry wall. It serves the same structural role as a steel angle lintel or wood header — spanning the opening and transferring the weight of the masonry and any superimposed loads (floors, roofs) on either side down to the jamb masonry below. In the USA, precast concrete lintels are standardized by the nominal wall width: 4", 6", 8", 10", and 12" wide units, all 7.625" (nominally 8") tall, manufactured in standard lengths from 16" to 144" or custom-cast on site. Two configurations are common: solid lintels (rectangular cross-section, fully precast) and U-lintels (channel-shaped, filled with grout and rebar on site — used in bond beam applications).
Per the Oberfields Concrete Lintel Design Guide (ACI 318 basis), when masonry is built continuously above a lintel, the load carried by the lintel is not the full weight of masonry to the next structural level — it is only the triangular "apex" zone formed by 45° lines rising from each end of the opening. This triangle has a height equal to half the effective span (L₂/2) and a base equal to L₂. The equivalent uniform load from this triangular zone is: W_apex = 0.33 × w × L₂ where w = CMU wall weight in psf and L₂ = effective span in feet. If masonry height above the lintel is less than L₂/2, the full masonry height is used instead — the calculator handles both cases automatically.
The calculator follows ACI 318-19 flexural and shear design for rectangular reinforced concrete beams, using the Oberfields apex load methodology for masonry load and the standard LRFD load combination (1.2D + 1.6L) for factored design moment and shear:
All standard USA precast concrete lintels share the same nominal 7.625" (8") height. The width matches the CMU wall. Self-weight per Oberfields and Tidewater Block lintel design guides, grouted solid:
| Lintel Size (W×H) | Actual Width | Eff. Depth d | Self-Weight (plf) | Min f'c | Typical Rebar |
|---|---|---|---|---|---|
| 4×8 (4" CMU) | 3.625" | 5.875" | ~25 lbs/ft | 3,000 psi | 1 × #4 Grade 60 |
| 6×8 (6" CMU) | 5.625" | 5.875" | 33 lbs/ft | 3,000–5,000 psi | 2 × #4 Grade 60 |
| 8×8 (8" CMU) | 7.625" | 5.875" | 50 lbs/ft | 5,000 psi | 2 × #5 Grade 60 |
| 10×8 (10" CMU) | 9.625" | 5.875" | 65 lbs/ft | 5,000 psi | 2 × #5 Grade 60 |
| 12×8 (12" CMU) | 11.625" | 5.875" | 83 lbs/ft | 5,000 psi | 2 × #6 Grade 60 |
| U-Lintel 6×8 | 5.625" | 5.875" (grouted) | ~33 lbs/ft | 5,000 psi | 2 × #5 (field placed) |
| U-Lintel 8×8 | 7.625" | 5.875" (grouted) | ~50 lbs/ft | 5,000 psi | 2 × #5 (field placed) |
Allowable superimposed load (plf) for standard USA precast concrete lintels at common spans — masonry self-weight only (apex zone), no superimposed floor or roof loads. Based on Oberfields and Tidewater Block design capacity tables, 5,000 psi f'c:
| Lintel Size | 3 ft Span | 4 ft Span | 6 ft Span | 8 ft Span | 10 ft Span | Max Span |
|---|---|---|---|---|---|---|
| 4×8 Solid | 900+ plf | 750 plf | 420 plf | 240 plf | — | ~8 ft |
| 6×8 Solid | 1,400+ plf | 1,100 plf | 660 plf | 390 plf | 250 plf | ~10 ft |
| 8×8 Solid | 2,000+ plf | 1,600 plf | 960 plf | 600 plf | 400 plf | ~12 ft |
| 10×8 Solid | 2,500+ plf | 2,000 plf | 1,200 plf | 760 plf | 510 plf | ~14 ft |
| 12×8 Solid | 3,000+ plf | 2,400 plf | 1,450 plf | 920 plf | 620 plf | ~16 ft |
The overall lintel length (what you order or cast) equals the clear opening span plus the bearing length at each end. With a 72" clear opening and 6" bearing each end, you order a 72 + 6 + 6 = 84" (7 ft) lintel. Standard precast lintels are available in 8" increments — always round up to the next standard length. Effective span L₂ used in structural calculations is measured center-to-center of the bearing surfaces — for 6" bearing, L₂ = clear span + 6" (one full bearing width added). Per Oberfields, this is the span used in all moment, shear, and deflection calculations.
Solid precast lintels are the standard choice for most USA residential and light commercial masonry openings — they arrive fully reinforced and ready to install. U-lintels (channel-shaped bond-beam lintels) are used when the opening is part of a continuous bond beam course in the masonry wall — the U-shape allows reinforcing bars to be threaded through the wall and the unit filled with grout on site, integrating the lintel into the structural masonry system. U-lintels are required by some seismic zone masonry codes and are preferred for walls requiring both lintel and bond beam function at the same course height. Both achieve the same structural performance when properly installed.
Standard precast lintels are designed for masonry self-weight loads only (apex zone). If your project involves floor or roof loads bearing onto the lintel, large openings over 10 ft, or high seismic zones, the lintel demand will likely exceed standard precast capacity. In these cases, a custom CIP or precast lintel with increased depth (12", 16", or 24") designed by a licensed PE is required. Per ACI 318, any lintel carrying more than the self-weight of masonry in its apex zone should have a project-specific structural calculation — especially for openings exceeding 8 ft in load-bearing walls.
This tool applies the ACI 318 / Oberfields apex load methodology to generate preliminary lintel size and capacity estimates for planning and budgeting purposes. For load-bearing walls, high seismic zones, openings over 10 ft, lintels supporting floor or roof framing, or any lintel in a building requiring engineered drawings, a licensed Structural Engineer (SE) or PE must provide a stamped design. Always verify lintel bearing conditions with the masonry contractor and confirm that the selected lintel matches the manufacturer's load table for the actual installed span and loading conditions before construction.
Manufacturer design guides, ACI standards, and sizing references for USA concrete lintel selection and installation.
Oberfields' Concrete Lintel Guide provides the authoritative USA design reference for solid and U-lintel load tables, apex load methodology, effective span calculations, bearing requirements, deflection limits, rebar schedules, and ACI 318 design formulas — used by masonry contractors and engineers across the USA for CMU wall lintel selection and verification.
Visit OberfieldsTidewater Block's Concrete Lintel Design Guide provides complete load capacity tables for 4×8 through 12×8 solid and U-lintels at all standard spans — including both standard (3,000 psi) and premium (5,000 psi) concrete series design capacities, useful for quick field verification of lintel adequacy for residential and commercial CMU wall openings.
Visit Tidewater BlockErnest Maier's Essential Concrete Lintel Size Guide covers the key considerations for selecting the correct lintel size in USA masonry construction — including load requirements, span measurements, bearing specifications, building code compliance (IBC / ACI 318), and how to interpret manufacturer load tables for both residential and commercial CMU wall applications.
Visit Ernest Maier