Reinforcement is bought by weight but designed by area — and the bridge between the two is a handful of standard diameters and one formula every engineer memorises. Here is the practical guide to rebar for Indian residential work.
Grades: what Fe500 and Fe550D mean
TMT bars to IS 1786 are graded by yield strength in N/mm²: Fe415, Fe500, Fe550 and their “D” variants (Fe500D, Fe550D) which guarantee higher ductility (greater elongation) — valuable in seismic zones. Fe500 and Fe500D dominate today’s market; the “D” grade is the better default for earthquake-resistant detailing.
Standard sizes and weight per metre
Weight per metre follows from the diameter: w = d²/162 kg/m (d in mm). This one formula converts every bar bending schedule into tonnage.
| Diameter | Weight (kg/m) | Area (mm²) | Typical use in a house |
|---|---|---|---|
| 8 mm | 0.395 | 50 | Stirrups, ties, slab distribution steel |
| 10 mm | 0.617 | 79 | Slab main bars, stair distribution |
| 12 mm | 0.888 | 113 | Slab/stair main bars, small beams, footing mesh |
| 16 mm | 1.580 | 201 | Beam main bars, column verticals |
| 20 mm | 2.469 | 314 | Column verticals, heavy beams |
| 25 mm | 3.858 | 491 | Heavily loaded columns, transfer members |
Which size goes where (typical residential pattern)
- Slabs: 8–10 mm main @ 125–200 c/c, 8 mm distribution.
- Beams: 12–16 mm top/bottom with 8 mm stirrups @ 100–200 c/c (closer near supports).
- Columns: 12–20 mm verticals with 8 mm ties; minimum four bars, 12 mm.
- Footings: 10–12 mm both ways @ 150–200 c/c.
- These are patterns, not prescriptions — actual sizes come from design for your spans and loads.
Bar bending schedule (BBS) basics
A BBS lists every bar mark: shape, cut length (including bend deductions and hooks), number, diameter, and total weight. It turns drawings into a purchasable steel order and is the estimator’s best defence against wastage — typical cutting wastage allowances run 3–5%.
Quality checks that take five minutes
- ISI mark, grade and manufacturer embossed on the bar; match the test certificate to the heat number.
- Light surface rust is acceptable; flaky, pitted rust is not.
- Bars should bend around the specified mandrel without cracking (ductility).
- Store on timber sleepers, off the ground, covered — not in the mud for six months.
Frequently asked questions
How do I calculate the weight of a steel bar?
Weight per metre in kilograms = d²/162, where d is the diameter in millimetres. A 16 mm bar weighs 16²/162 ≈ 1.58 kg per metre; a standard 12 m length weighs about 19 kg.
Is Fe500D better than Fe500?
They have the same design yield strength (500 N/mm²), but Fe500D guarantees higher ductility (minimum elongation) — a meaningful advantage for earthquake resistance, and generally the preferred choice in seismic zones III–V.
What bar sizes does a typical G+2 house use?
Most commonly 8 mm (stirrups/ties/distribution), 10–12 mm (slabs, footings) and 16–20 mm (beams and columns). The actual design mix of sizes must come from structural calculations for your specific spans and loads.