TryBuildCalcRoof Beam Steel Calculator(Main Bars, Top Bars, Stirrups, Steel Weight & Procurement)
Estimate roof beam reinforcement steel, stirrups, wastage, and approximate 12 m bar procurement. Adjust beam shape, size, bar diameter, stirrup spacing, cover, laps, and wastage for your reinforcement estimate.
Calculate RCC beam reinforcement, stirrups, steel weight, wastage, and 12 m bar procurement.
🕒 Last updated: August 6, 2026
Inputs
Beam Dimensions
ℹ️T-beam and L-beam use web + flange geometry; stirrups wrap the web only, not the full flange width.
ℹ️Clear span of beam. Allowed range after conversion: 1 m to 20 m.
ℹ️Typical residential beam width: 200-300 mm. Allowed range after conversion: 100-1000 mm.
ℹ️Typical residential beam depth: 300-600 mm. Allowed range after conversion: 200-2000 mm.
ℹ️Enter how many identical beams should be included in the estimate.
Main Bars
ℹ️Bottom face bars. Minimum 2 bars for most rectangular beams.
Top Bars
ℹ️Top hanger bars or support reinforcement as shown in structural drawings.
Stirrups
ℹ️Spacing is center-to-center. IS 456 limits depend on effective depth and shear design.
Cover and Extras
ℹ️Typical beam cover: 25 mm for mild exposure, 30 mm for moderate exposure, and 40 mm for severe exposure.
Optional
ℹ️Lap length is added where straight bar cutting length exceeds a 12 m stock bar.
ℹ️Lap length = multiplier x bar diameter.
Net Beam Steel
105.16 kg
Main bars: 12
Top bars: 8
Stirrups: 108
Total length: 189.16 m
Recommended Procurement
110.42 kg
Wastage (5%): 5.26 kg
Concrete volume: 1.104 m³
Steel consumption: 95.3 kg/m³
Steel percentage: 0.492%
Check: Within broad RCC beam reinforcement range
Weight Contribution
Beam Steel Breakdown
| Bar Type | Diameter | Spacing / Count | Total Bars | Cutting Length | Total Length | Weight |
|---|---|---|---|---|---|---|
| Main bars | 12 mm | 3 per beam | 12 | 3.95 m | 47.4 m | 42.13 kg |
| Top bars | 10 mm | 2 per beam | 8 | 3.95 m | 31.6 m | 19.51 kg |
| Stirrups | 8 mm | 150 mm c/c | 108 | 1.02 m | 110.16 m | 43.52 kg |
| TOTAL | - | - | 128 | - | 189.16 m | 105.16 kg |
Steel Percentage Check
Main bar area: 339.29 mm²
Gross beam section: 69,000 mm²
Main steel %: 0.492%
Status: Within broad RCC beam reinforcement range
Procurement Summary
Total steel weight (net): 105.16 kg
Steel per metre: 6.57 kg/m105.16 ÷ 16 = 6.57 kg/m
Steel consumption: 95.3 kg/m³105.16 ÷ 1.104 = 95.3 kg/m³
Wastage (5%): 5.26 kg
Total to procure: 110.42 kg
Stirrup Spacing Check
Maximum recommended spacing: 202 mm
Provided spacing: 150 mm
✓ Within recommended range
Check uses min(0.75d, 300 mm), where d is the approximate effective beam depth.
Equivalent 12 m Bars by Diameter
5 Nos 12 mm5 bars (44.24 kg)
3 Nos 10 mm3 bars (20.49 kg)
10 Nos 8 mm10 bars (45.7 kg)
Need the actual cutting length for these bars and stirrups, including bends and hooks? Bar Bending Schedule Calculator →
Sizing reinforcement for a lintel over a door or window opening rather than a full beam? Lintel Calculator →
Approximate results for planning only. Verify with a professional.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Beam Steel Calculator.
Roof beam steel estimate
This page is useful for estimating steel in multiple smaller roof beams.
This calculator page is pre-filled for the selected beam case. Edit any input and the worked example updates from the active values.
- Default beam depth: 300 mm.
- Number of beams: 4.
- Main bars: 12 mm.
How does the beam steel calculator work?
Beam steel quantity is calculated separately for main bars, top bars, and stirrups. Each component uses the beam dimensions, bar diameter, concrete cover, and spacing to estimate total steel length and weight. All three are then combined for total procurement quantity.
Step 1 — Calculate Effective Beam Length
Effective Length = Beam Length − (2 × Cover)
Concrete cover is deducted from both ends of the beam before calculating bar cutting lengths and stirrup count. This ensures bars do not extend to the outer face of the beam where they would be exposed. This step is identical for every beam shape.
Step 2 — Calculate Main Bar Cutting Length and Weight
Main bars run along the bottom face of the beam for the full effective length, regardless of beam shape. Each bar is cut to the effective length. If the effective length exceeds 12 m (standard stock bar length), a lap splice is added.
Main bar cutting length = Effective Length
If lap required: Main bar cutting length = Effective Length + (Lap Multiplier × Diameter)
Total main bar length = Cutting length × Number of main bars × Number of beams
The total bar length is then converted into weight using the standard unit weight formula for steel bars, where D is the bar diameter in millimetres.
Unit weight = D² ÷ 162 kg/m
Main bar weight = Total main bar length × Unit weight
The D²/162 formula is derived from the density of steel (7850 kg/m³) and the cross-sectional area of a circular bar. It is the standard formula used across Indian construction sites for quick steel weight estimation.
Step 3 — Calculate Top Bar Cutting Length and Weight
Top bars (hanger bars or compression bars) run along the top face of the beam. They use the same effective length as the main bars and are calculated using the same unit weight formula with the top bar diameter.
Top bar cutting length = Effective Length
Total top bar length = Cutting length × Number of top bars × Number of beams
Top bar unit weight = Top bar D² ÷ 162 kg/m
Top bar weight = Total top bar length × Top bar unit weight
Step 4 — Calculate Stirrup Cutting Length
Stirrups are closed rectangular links that wrap around the longitudinal bars. For a Rectangular beam, their inner dimensions come from the full beam width and depth. For a T-beam or L-beam, stirrups confine the web (the stem below the slab) only — not the full flange width — so their inner dimensions come from the web width and web depth (overall depth minus flange thickness) instead. In both cases, cover is deducted from both sides, and the cutting length includes the full perimeter plus a hook allowance for the two closed ends.
Rectangular: Inner width = Beam Width − (2 × Cover); Inner depth = Beam Depth − (2 × Cover)
T-beam / L-beam: Inner width = Web Width − (2 × Cover); Inner depth = (Overall Depth − Flange Thickness) − (2 × Cover)
Stirrup perimeter = 2 × (Inner width + Inner depth)
Hook allowance = 2 × 10d (two hooks, 10d each)
Stirrup cutting length = Stirrup perimeter + Hook allowance
Where d is the stirrup bar diameter in millimetres. The hook allowance accounts for the two bent ends of the closed stirrup. A hook of 10d is standard per IS 2502 and is consistent with IS 13920 requirements for seismic detailing.
Stirrup inner dimensions must be calculated after deducting cover from both sides — not from the outer beam face. Using outer dimensions overestimates the stirrup perimeter and produces an incorrect cutting length. For T-beam/L-beam, using the flange width instead of the web width would substantially overestimate stirrup steel.
Step 5 — Calculate Number of Stirrups
The number of stirrups is calculated by dividing the effective beam length by the stirrup spacing, then adding one stirrup for the starting end.
Number of stirrups per beam = floor(Effective Length ÷ Stirrup Spacing) + 1
Total stirrups = Number of stirrups per beam × Number of beams
The floor function rounds down to the nearest whole number because partial stirrup intervals are not physically possible. Adding 1 accounts for the stirrup at the starting end of the beam which the division alone does not count.
Step 6 — Calculate Stirrup Weight
Stirrup unit weight = Stirrup D² ÷ 162 kg/m
Total stirrup length = Total stirrups × Stirrup cutting length
Stirrup weight = Total stirrup length × Stirrup unit weight
Step 7 — Calculate Total Steel Weight and Procurement Quantity
Net steel weight = Main bar weight + Top bar weight + Stirrup weight
Wastage amount = Net steel weight × Wastage %
Total to procure = Net steel weight + Wastage amount
Wastage accounts for cutting offcuts, bending losses, handling, and site wastage. A typical allowance for beam steel is 5% for straightforward residential beams. The total procurement quantity is then divided by bar type and converted to equivalent 12 m bar counts for ordering.
Step 8 — Check Main Bar Steel Percentage
The main bar steel percentage is checked against IS 456 limits to verify the entered configuration is within acceptable bounds. This is a cross-check, not a structural design verification. For T-beam/L-beam, the gross area used here is the true cross-section (web area plus flange area), not width × depth.
Rectangular: Beam gross area = Beam Width × Beam Depth (mm²)
T-beam / L-beam: Beam gross area = (Web Width × Web Depth) + (Flange Width × Flange Thickness) (mm²)
Main bar area = (π ÷ 4 × D²) × Number of main bars (mm²)
Steel % = (Main bar area ÷ Beam gross area) × 100
| IS 456 Limit | Value | Note |
|---|---|---|
| Minimum tensile reinforcement | ≈ 0.17% for Fe 500 | Based on 0.85 bw d / fy |
| Maximum reinforcement | 4% of gross area | Both tension and compression |
Worked Example
This example uses the active inputs above and follows the same steps as the Formula section.
Input Values Used
| Input | Value |
|---|---|
| Beam Shape | Rectangular Beam |
| Length | 4 m |
| Width | 230 mm |
| Depth | 300 mm |
| Number of Beams | 4 |
| Main Bars | 3 bars of 12 mm |
| Top Bars | 2 bars of 10 mm |
| Stirrups | 8 mm @ 150 mm c/c |
| Concrete Cover | 25 mm |
| Wastage | 5% |
Step 1 — Calculate Effective Beam Length
| Calculation | Substitution | Result |
|---|---|---|
| Effective Length = Beam Length − (2 × Cover) | 4 − (2 × 0.025) | 3.95 m |
Step 2 — Calculate Main Bar Cutting Length and Weight
Main bars run the full effective length of the beam. The cutting length per bar equals the effective length. Total length is then multiplied by the number of bars and number of beams.
| Calculation | Substitution | Result |
|---|---|---|
| Cutting length per bar = Effective Length | From Step 1 | 3.95 m |
| Total main bar length = Cutting length × Bars × Beams | 3.95 × 3 × 4 | 47.4 m |
| Main bar weight = Total length × Unit weight (12² ÷ 162) | 47.4 × 0.889 | 42.13 kg |
Step 3 — Calculate Top Bar Cutting Length and Weight
Top bars use the same effective length as main bars and are calculated separately using the top bar diameter.
| Calculation | Substitution | Result |
|---|---|---|
| Total top bar length = Cutting length × Bars × Beams | 3.95 × 2 × 4 | 31.6 m |
| Top bar weight = Total length × Unit weight (10² ÷ 162) | 31.6 × 0.617 | 19.51 kg |
Step 4 — Calculate Stirrup Cutting Length
The stirrup inner dimensions are calculated after deducting cover from both sides of the beam width and depth. The perimeter of this inner rectangle gives the base cutting length, plus two hooks at 10d each for the closed ends.
| Calculation | Substitution | Result |
|---|---|---|
| Inner width = Beam Width − (2 × Cover) | 230 − (2 × 25) | 180 mm |
| Inner depth = Beam Depth − (2 × Cover) | 300 − (2 × 25) | 250 mm |
| Stirrup perimeter = 2 × (Inner width + Inner depth) | 2 × (180 + 250) | 860 mm |
| Hook allowance = 2 × 10 × Stirrup Diameter | 2 × 10 × 8 | 160 mm |
| Stirrup cutting length = Perimeter + Hook allowance | 860 + 160 | 1.02 m |
Step 5 — Calculate Number of Stirrups
| Calculation | Substitution | Result |
|---|---|---|
| Stirrups per beam = floor(Effective Length ÷ Spacing) + 1 | floor(3.95 ÷ 0.15) + 1 | 27 stirrups |
| Total stirrups = Stirrups per beam × Beams | 27 × 4 | 108 stirrups |
Step 6 — Calculate Stirrup Weight
| Calculation | Substitution | Result |
|---|---|---|
| Total stirrup length = Total stirrups × Cutting length | 108 × 1.02 | 110.16 m |
| Stirrup weight = Total length × Unit weight (8² ÷ 162) | 110.16 × 0.395 | 43.52 kg |
Step 7 — Calculate Total Steel Weight and Procurement Quantity
| Component | Weight |
|---|---|
| Main bars (3 × 12 mm) | 42.13 kg |
| Top bars (2 × 10 mm) | 19.51 kg |
| Stirrups (8 mm @ 150 mm) | 43.52 kg |
| Net steel weight | 105.16 kg |
| Wastage (5%) | 5.26 kg |
| Total to procure | 110.42 kg |
Step 8 — Check Main Bar Steel Percentage
The main bar steel percentage checks whether the entered configuration falls within IS 456 limits for beam reinforcement. This is a quantity cross-check — not a structural strength verification.
| Calculation | Substitution | Result |
|---|---|---|
| Beam gross area = Width × Depth | 230 × 300 | 69,000 mm² |
| Main bar area = (π ÷ 4 × D²) × Number of bars | (π ÷ 4 × 12²) × 3 | 339.3 mm² |
| Steel % = (Main bar area ÷ Gross area) × 100 | (339.3 ÷ 69,000) × 100 | 0.492% |
| Check | Limit | Result | Status |
|---|---|---|---|
| IS 456 Maximum | 4.000% | 0.492% | ✓ Within limit |
Therefore, for the entered rectangular beam configuration across 4 beams, the total steel required is approximately 105.16 kg net and 110.42 kg for procurement including 5% wastage.
Cross-check against the Quick Reference Tables in the complete Beam Steel Calculator.