Dimensions. D is the overall circular concrete member diameter; c is uniform clear cover to the stirrup’s outside face; d is stirrup bar diameter. Outside diameter Do = D − 2c, bar-centreline diameter Dc = Do − d, and internal diameter Di = Do − 2d.

Approximate circular length. IS 2502:1963 does not tabulate a circular closed-link cutting-length shape. This calculator adopts the practical site/BBS method: circular body = πDc, add two hook extensions, then deduct 3d for each of the two 135° bends. It does not reuse the rectangular Table VIII-A allowance or its 24d term.

Straight tail requirements. IS 2502:1963, clause 3.3, requires at least 8d straight extension beyond the end curve. IS 13920:2016, Amendment No. 1 (September 2017), clause 6.3.1(a) and Figure 4, specifies 8d with a 75 mm minimum for the referenced seismic link detail. The saved preset adopts the greater value. Both refer to the straight extension, not the complete curved hook length. IS 2502 / IS 13920 — code book downloads

Adopted site convention. Each hook length T = max(8d, 75 mm). Add two hook lengths and deduct 3d for each 135° hook bend: L = π(D − 2c − d) + 2T − 6d. This is a practical estimating convention, not an exact circular-stirrup equation prescribed by IS 2502 or IS 13920. It does not calculate the complete developed hook arcs. The circular body has no discrete 90° corner bends.

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.

Scope. This tool estimates one circular closed-link shape with uniform cover. It does not design reinforcement, choose required cover, determine lap or weld details, check hook/bend radius or fit around longitudinal bars, or include spirals/helices. Seismic diameter must be at least 8 mm; some column details require 10 mm or more. Verify the approved drawing, BBS and fabricator’s required developed hook geometry before cutting.

IS code books used in civil engineering — PDF downloads