CIVIL PRACTICAL KNOWLEDGE
Calculate cutting length, stirrup quantity and nominal steel weight—with the method shown.
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Enter the dimensions from your drawing.
For identical complete helices.
Lapping is calculated automatically for 12 m stock bars: 1½ pitched turns per splice, following IS 5525:1969 clause 6.11.1. The added lap length is included in cutting length and steel weight.
* Required fields. Cover is measured to the outside of the stirrup.
Complete the details, then calculate to see lengths, weights and every step.
Scheduled cutting length / helix including laps
Total scheduled length
Before wastageTotal weight & wastage
Before wastage:SHAPE REFERENCE
Smooth helix measured along the bar centre line. No separate 90°/135° hook allowances or corner deductions. Main bars are illustrative.
Default: 1½ flat anchorage turns at each end. Confirm the approved drawing.
Estimate includes automatic 1½-turn laps using 12 m stock bars. Confirm the lap arrangement and permitted splice locations against the approved drawing/BBS, and check a trial helix before batch cutting. End transitions, separate closure rings, variable pitch and seismic confinement design are excluded. Stock-piece count is a minimum estimate; individual cuts and offcuts need a fabrication plan.
Dimensions. D and H are overall concrete diameter and height. Cover c is measured to the outside of the spiral, including at both ends. Bar diameter d. Helix centre-line diameter Dc = D − 2c − d; available centre-line rise h = H − 2c − d. P is centre-to-centre axial pitch, not clear spacing.
Helical length. Active turns N = h/P; fractional turns remain fractional. One turn length l = √[(πDc)² + P²]. Geometric length before laps L₀ = Nl + 2eπDc, with e additional flat turns at EACH end. This follows the geometric helix equation; it is not an IS fabrication-length equation. University of Luxembourg — helix length derivation.
End anchorage. IS 456:2000 clause 26.5.3.2(d)(1) refers to 1½ extra turns for end anchorage; IS 5525:1969 clause 6.11.1 explicitly describes 1½ turns at both top and bottom. This estimate adopts e = 1.5 at each end and measures these as flat circumferential turns, like the closure shown in the reference. End-turn transitions and actual packing are not developed here; use the approved BBS. The input may be changed to the specified allowance. Zero provides no end anchorage allowance. Separate closure rings are excluded. Automatic splice laps are added separately and do not change with e.
Fixed seismic context. The shared interface retains an 8–25 mm bar range with no ordinary/seismic selector. This does not establish compliance with IS 13920. Confinement, pitch limits, bar size, core dimensions, splices and anchorage must be checked by the designer. Square/rectangular bend deductions and 135° hook tails do not apply to this helix.
Scheduling & quantities. IS 2502:1963 clause 5.1.1 specifies the next greater whole 25 mm of the bending dimensions and allowances, not nearest-25 rounding. Scheduled length = ceil(calculated length ÷ 25) × 25; an exact multiple is unchanged. Table XI cutting tolerance is separate. Quantities and weights use this scheduled length. Wastage does not change the stirrup’s cutting length or count.
Display units. Lengths show mm, inches and feet, with the selected member unit first. Whole-unit display rounds fractions greater than .500 upward and exactly .500 downward. Feet use construction notation such as 5’2″ ft. Display rounding never changes the underlying geometry, cutting schedule or steel weight; calculation substitutions retain precision in mm.
Nominal mass. Standard diameters use IS 1786:2008 Table 1 masses: 6 mm = 0.222, 8 mm = 0.395, 10 mm = 0.617, 12 mm = 0.888, 16 mm = 1.58 kg/m. Other supported standard sizes use the same table. Nonstandard custom diameters use πd²/4 × 0.00785 kg/m, assuming steel density 7,850 kg/m³.
Automatic laps with 12 m stock. IS 5525:1969 clause 6.11.1 specifies a spiral lap of 1½ turns. This estimate assumes the splice follows the active pitched helix: lap a = 1.5 × √[(πDc)² + P²]. This is a spiral-specific overlap, separate from flat end anchorage turns; no generic 40d/50d longitudinal-bar lap is used. For the geometric helix length L₀ scheduled upward to 25 mm, minimum pieces n = max(1, ceil((scheduled L₀ − a)/(12,000 − a))). A helix fitting within 12 m uses one piece and adds no lap. Splices = n − 1; added lap length = (n − 1)a. Cutting length including laps = L₀ + (n − 1)a, then scheduled upward to 25 mm. If a required lap reaches 12 m, this stock-bar method cannot be used. Confirm the splice arrangement and project detailing; the tool does not authorize a seismic lap, choose splice positions, or optimize offcuts. IS 5525:1969 clause 6.11.1 — code book downloads.
Scope. Constant-diameter, constant-pitch helix; uniform side/end cover; identical assemblies. No structural design, variable confinement zones, bend-radius check, individual piece cutting schedule, or separate closure-ring length. Pitch must exceed bar diameter and fit within the available rise. Verify actual end geometry and a trial helix against the approved drawing/BBS.