TryBuildCalcWindow Lintel CalculatorLintel estimator for window openings
Calculate concrete, steel, and shuttering quantity for an RCC lintel over a door or window opening.
🕒 Last updated: August 10, 2026
Basic Dimensions
ℹ️Clear width of the door/window opening, not the lintel's own length.
ℹ️Commonly 150 mm minimum on each side for typical openings — confirm against your project's structural drawing.
ℹ️A lintel normally spans the full wall thickness.
ℹ️Rule of thumb: span ÷ 10 to span ÷ 12, with a practical minimum of ~150 mm.
ℹ️Set to more than 1 if several openings share the same lintel size.
Material Details
Reinforcement
ℹ️Commonly 100-150 mm centre-to-centre for residential lintels.
Cost
For 1 lintel of 1.50 m (4.92 ft) each (span + bearing), you need approximately 0.054 m³ of concrete and 4.9 kg of reinforcement steel.
Concrete
Concrete volume: 0.054 m³ (1.92 cft)
Cement: 0.4 bags
Sand: 0.023 m³ (0.81 cft)
Aggregate: 0.046 m³ (1.61 cft)
Steel Reinforcement
Main (Bottom) Bars: 2 × 10 mm
Stirrups: 11 × 8 mm
Total steel weight: 4.9 kg
Shuttering
Soffit area: 0.35 m²
Side faces: 0.45 m²
Total contact area: 0.79 m² (8.6 sqft)
| Bar Type | Diameter | Count / Spacing | Cutting Length | Total Length | Weight |
|---|---|---|---|---|---|
| Main (Bottom) Bars | 10 mm | 2 | 1.450 m | 2.90 m | 1.79 kg |
| Stirrups | 8 mm | 150 mm c/c (11/lintel) | 0.720 m | 7.92 m | 3.13 kg |
Assumptions Used
Lintel length = clear span + bearing on both sides | Steel weight: d² ÷ 162 (kg/m) | Stirrup hook allowance: 10 × diameter per end | Concrete dry volume factor: 1.54
Unsure about bearing length or depth for your opening span? Lintel Design Guide →
Diagram simplified for clarity (not to scale). Illustrative only.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Lintel Calculator.
Lintel sizing for a window opening
This page is pre-filled with a typical 1.2 m window opening and a 230 mm × 150 mm lintel — a common residential window size for a 230 mm wall.
Window openings often carry more of the wall's height above them than a door (since there's masonry both above and, on an external wall, below the window too), so bearing length and depth deserve a careful check against your structural drawing rather than the rule-of-thumb minimum alone.
- 1.2 m spans commonly use 150 mm bearing each side and a 150 mm minimum practical depth.
- Wider windows (bay windows, sliding windows) need a deeper lintel — check the Reference Tables on the complete calculator page.
- Edit the span, wall thickness, or reinforcement above to match your actual window opening.
How Is the Lintel Quantity Calculated?
The calculation happens in four parts — lintel length, concrete quantity, steel reinforcement, and shuttering area — then an optional cost estimate on top.
Step 1 — Lintel Length
Lintel Length = Opening Span + (2 × Bearing Length)
The lintel must rest on solid wall beyond the opening on both sides — its true length is always longer than the opening it spans.
Step 2 — Concrete Volume
Wet Volume = Length × Width × Depth (per lintel, × count for multiple openings)
Dry Volume = Wet Volume × 1.54
Cement Bags = Cement Volume ÷ 0.0347 m³/bag (50 kg bags)
Dry volume accounts for the voids between aggregate particles that disappear once the concrete is mixed and compacted. The dry volume is then split into cement, sand, and aggregate using the selected mix ratio, and the wastage percentage is applied once to the final quantities.
Step 3 — Steel Reinforcement
Bar Length (each bar) = Lintel Length − (2 × Concrete Cover)
Stirrups per Lintel = ⌊(Lintel Length ÷ Spacing)⌋ + 1
Stirrup Cutting Length = 2 × (Width − 2×Cover + Depth − 2×Cover) + Hook Allowance (2 × 10 × diameter)
Unit Weight (kg/m) = Diameter² ÷ 162
Main and top bars run the length of the lintel minus end cover; stirrups are closed loops sized to the concrete section minus cover on each side, with a hook allowance added at both ends to close the loop.
Step 4 — Shuttering Area
Soffit Area = Width × Length
Side Area = 2 × Depth × Length
Total Contact Area = (Soffit + Side Area) × Count
Shuttering supports the underside (soffit) and both vertical faces of the lintel until the concrete gains enough strength to be self-supporting — the wall itself typically forms the end shuttering, so no separate end panels are counted.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Opening span | 1.2 m | Fixes the clear opening width the lintel must bridge |
| Bearing length (each side) | 150 mm | Adds the extra length resting on solid wall on both sides, setting the true lintel length |
| Lintel width × depth | 230mm × 150mm | Sets the concrete cross-section and the shuttering side area |
| Mix ratio / wastage | 1:1.5:3, 5% wastage | Converts wet volume to cement bags and adds a buffer for site losses |
| Cover / bar diameter / spacing | 25 mm cover, 10 mm main × 2, 8 mm stirrups @ 150 mm | Sets bar cutting length (span minus cover) and stirrup count/size |
| Number of openings | 1 | Multiplies every final quantity for identical repeated lintels |
Step 1 — Lintel Length
| Calculation | Substitution | Result |
|---|---|---|
| Opening span | 1.2 m | 1.200 m |
| Bearing (each side) | 150 mm | 0.150 m |
| Lintel length | 1.200 + 2 × 0.150 | 1.500 m (4.92 ft) |
Step 2 — Concrete
| Calculation | Substitution | Result |
|---|---|---|
| Wet volume | 1.50 × 230mm × 150mm × 1 | 0.052 m³ |
| With 5% wastage | 0.052 × 1.05 | 0.054 m³ (0.4 bags) |
Step 3 — Steel
| Bar Type | Substitution | Weight |
|---|---|---|
| Main (Bottom) Bars | 2 × 1.450 m × 10²÷162 | 1.79 kg |
| Stirrups | 11 × 0.720 m × 8²÷162 | 3.13 kg |
| Total steel | Sum of all rows | 4.92 kg |
Therefore, 1 lintel of 1.50 m each needs 0.054 m³ of concrete, 4.9 kg of steel, and 0.79 m² of shuttering.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.