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How to use the lintel calculator

The beam over an opening in a masonry wall: what each input means, how the load triangle and arching work, and why the anchorage governs short lintels.

All guides Inputs Result Calc sheet Walk-through Mistakes

1. What the calculator does

The lintel calculator designs the beam over a door or window in a masonry wall: a reinforced masonry lintel, a cast-in-situ RC lintel, or a precast prestressed lintel (for which it works out the loads and the bearing). It finds the load on the lintel from the masonry above, using the load triangle and arching where the wall above is tall enough, adds the floor or roof load if it bears within reach, and checks bending, shear, the anchorage of the bars, the end bearing and deflection.

The page badge lists what it uses: the SANS 10400-K Annex B load triangle, SANS 10160-1 combinations, SANS 10164-2 for reinforced masonry, SANS 10100-1 for RC, and SANS 10164-1 5.4.3 for bearing.

Lintel calculator header with the PASS badge — The header: PASS 89 %, governed by the end anchorage on the left.

2. The inputs, group by group

Input	What it means	Typical value
Lintel	The lintel type: reinforced masonry, cast-in-situ RC or precast prestressed.	reinforced masonry
Opening	Clear opening, more openings in the same wall, bearing at each end and the wall thickness.	1800 mm, bearing 350, wall 230
Above	Height of masonry above to the floor or roof, and the wall beside the opening on the shorter side.	2400 mm above, 600 beside
Loads	Characteristic G and Q from the slab or roof, and where it bears. Point loads under the link.	8 / 2 kN/m on the wall above
Section	Width and depth of the lintel.	230 × 340
Bars	Bottom bars (auto = least area), links, cover and the infill concrete.	auto, no links, cover 40, grade 25

Lintel inputs: type, opening, above, loads, section and bars — The inputs. The masonry above and the wall beside the opening decide whether the wall can arch over the lintel.

3. How to read the result

The elevation draws the opening, the lintel and the masonry above, with the 60° load triangle and the zone where the slab load is picked up. When the wall above is tall enough, only the triangle loads the lintel (arching); a short wall or a load inside the zone adds more.

Lintel elevation with the load triangle and arching — Elevation: arching, H_t 1715 mm, the 60° triangle over the 1800 mm opening, 2Y10 in the lintel.

Load on the lintel and the section — Load on the lintel: M 4.89 kNm and V 7.16 kN from the governing combination; the 230 × 340 section.

The design result gives the analysis span and whether the wall arches, the design moment and shear, the end reaction, the bars against the area required, the links, the end bearing and the deflection.

Design result and bending schedule card for the lintel — Design result: span 2150 mm with arching, 4.89 kNm / 7.16 kN, 2Y10 = 157 mm² (45 required), no links needed; the bending schedule card.

The badge names the governing check; here the anchorage of the bars at the left end. Short lintels with small bars are usually governed by the anchorage over the bearing, not by bending. Note the “not checked” on the end bearing row of this example: a NOT CHECKED item is not a pass, so check that bearing yourself or give the input it needs.

Design checks summary for the lintel — Design checks: SANS 10164-2 · 17 pass.

4. Calc sheet and schedule

The result (pass / fail and utilisation) stays free for everyone. Every check with its clause, the calc sheet and the bending schedule are open to signed-in users. Sign in free: 3 designs a month (one calculator, open for 24 hours). Unlimited with a calculator pack.

The bending schedule card reads: “Sign in (free): 3 schedules a month. CSV with a paid plan.”

5. A 2-minute walk-through

Open the calculator: an 1800 mm opening in a 230 mm wall, 2400 mm of masonry above, slab G 8 and Q 2 kN/m on the wall above.
Read the badge: PASS 89 %, end anchorage.
Cut the masonry above to 600 mm and see arching lost and the load jump.
Widen the opening to 2400 mm and see the bars change.
Switch to a precast prestressed lintel and compare.

6. Common mistakes

Counting on arching without the masonry to arch. It needs enough wall above and beside the opening, and no opening in the triangle.
Short bearings. The bars need room to anchor, and the masonry under the end needs area to carry the reaction.
Floor or roof loads ignored. A slab or a truss bearing within the zone above loads the lintel directly.
Ultimate loads in the load boxes. They take characteristic G and Q.

7. Where it fits

The wall itself is checked in the masonry wall calculator; the slab or roof loads come from the load take-down.

8. Learn more

Try it nowThe calculator opens with the walk-through inputs above. The result is free; sign in for the checks, calc sheet and schedule.
Open the lintel calculator

A guide to using the calculator, not a design. Check every value against the current code and your own project, and have the design checked and signed by a registered professional engineer.

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