Steel Bar Sizes for a House: Which TMT Diameter Goes in Footings, Columns, Beams and Slabs

TL;DR: Steel bar sizes for house construction in India mostly run from 8 mm to 16 mm TMT, with thicker bars in columns and beam bottoms and thinner bars in slabs and stirrups. For a G+1 house, Indian thumb-rule guides such as the Interior Company column guide list 6 bars of 12 mm with 8 mm stirrups at 6-inch spacing in a 9"x12" column. According to Amba Shakti Steels, common practice in Indian house slabs is 10 mm main bars with 8 mm distribution bars. Footings do not automatically need thicker bars than beams, because footing steel is set by design rather than by ranking members. Any thumb-rule size is only a starting point: the structural engineer's drawing and bar schedule override every table, including the one below.

Most house members take 8 mm to 16 mm TMT bars, and the drawing decides which

A TMT bar is ribbed reinforcing steel that has been thermo-mechanically treated. The hot bar is water-quenched and then self-tempers, which gives it a hard outer layer and a ductile core. Builders in Bangalore still call it Tor steel or saria. Every part of a house that bends depends on it, because concrete, as AsktheBuilder's Tim Carter explains, has only about one-tenth as much strength in tension as in compression.

Radha TMT, a competing manufacturer, lists 8 mm, 10 mm and 12 mm as the sizes most commonly used in individual houses, with 16 mm kept for heavier columns and foundations. Its guide adds that an ordinary house rarely needs 20 mm or 25 mm bars, and that over-specifying them mostly adds cost. Amrit Steels, a Bangalore wholesale dealer trading since 1972, stocks every standard diameter from 8 mm to 32 mm in 12-metre lengths.

Use the table below to spot an odd line on a G+1 (ground plus one storey) order list. It is not a design.

Why do the diameters differ between members?

Three things drive the choice: load, span and cover. A column carries every floor above it, while a slab spreads a lighter load across a wide area using thin bars at close spacing. Interior Company's guide lists the factors that change what a column needs: floors, beam load, slab thickness, soil bearing capacity, column height, span and building use. That is why one table cannot fit every house.

Cover is the concrete between the outermost bar and the surface, and it protects the steel from moisture. Putting thicker bars inside a member of fixed size reduces that cover and crowds the concrete, so a thicker bar is not automatically a safer one.

A G+1 column commonly uses six 12 mm bars with 8 mm stirrups

The most repeated Indian thumb rule for a two-storey house column has four parts:

• a 9"x12" (225 mm x 300 mm) column

• six 12 mm bars

• 8 mm stirrups at 6-inch spacing

• M20 concrete

Interior Company carries this rule in a table credited to Civilsite, and a G+1 project plan uploaded to Scribd repeats it with Fe500 steel. Guides differ on the bar count, though. A CIVIL Engineering Tutorials video gives 4 to 6 bars of 12 mm in 9"x9" or 9"x12" columns for one- and two-storey buildings. Interior Company treats four 12 mm bars in a 9"x9" column as the minimum for any house column, not as the G+1 norm.

Bar count matters as much as diameter. Ramkumar Menon, a chartered civil engineer, writes that the steel area of a section matters more than the bar diameter, and that the design criteria of IS 456-2000 govern. The arithmetic shows why. A 12 mm bar has a cross-section of about 113 mm² (π/4 × 12²), so six bars give roughly 679 mm² and four give roughly 452 mm², which is a third less steel in the same column.

From G+2 upward, 16 mm bars start to appear, but the guides disagree on the layout. The same tutorial uses 6 to 8 bars of 16 mm or 20 mm for three- and four-storey buildings. Interior Company's G+3 table mixes four 16 mm bars with two 12 mm bars. Menon prefers 16 mm bars on a G+2 ground floor, stepping down to 12 mm above.

Stirrups and ties use 8 mm in most Indian thumb rules

A stirrup (called a tie in a column) is a closed loop of thin bar wrapped around the main bars to hold them in position and resist shear. The Indian G+1 guides agree on 8 mm stirrups at 6-inch spacing. The tutorial's range runs from 8 to 10 mm, and Tameer Steel's supplier guidance lists 6 mm or 8 mm column ties. Whatever size the drawing shows, the check is that the order matches it.

Beams put the thicker bars at the bottom, where tension develops

A loaded beam sags. Its bottom face stretches and its top is squeezed, so the heavier steel goes underneath. One G+1 plan specification on Scribd gives a 9"x12" beam the following steel:

• four 12 mm Fe500 bars at the bottom

• two 10 mm bars at the top

• 8 mm stirrups at 6-inch centres

• 25 mm of clear cover

The plinth beam in that plan follows the same pattern, with 10 mm recommended for the top bars. The same document details its roof beam differently, with 12 mm bars throughout, which shows how much beams can vary within one house.

None of the thumb rules we could verify cover lintels over doors and windows, so lintel bars should match the drawing line for line. No published guide links a beam's span to its bar size either, which is why a 16-foot beam cannot be sized by eye.

Which mm rod is used for slabs? Usually 10 mm main and 8 mm distribution

Main bars carry a slab's load across its span. Distribution bars run at right angles to spread that load and control cracking. In Indian house slabs, the common pattern Amba Shakti Steels describes is 10 mm main bars with 8 mm distribution bars. Tameer Steel adds that 12 mm comes in for heavier loads, such as car parks or thicker slabs, and that oversized slab bars cause congestion and poor compaction. Thin bars at close spacing control cracking better than thick bars set far apart.

Can 8 mm be the main bar in a slab?

Practitioners disagree on this. Amba Shakti Steels says that 8 mm bars are not typically enough as primary reinforcement in most roof slab designs. Others accept 8 mm main bars in residential slabs with short spans and close spacing. Engineers also disagree on what IS 456 allows here, and none of the sources we reviewed quotes the clause itself. Treat an all-8 mm slab as an exception the engineer has to justify. Be most cautious with cantilevered chajjas and balconies, where undersizing carries the most risk.

Floor area alone tells you nothing about slab bars. A veteran construction practitioner was asked whether 8 mm bars would do for a 1,200 sq ft slab. In the reply on Quora, the practitioner first asked for the spans, the support conditions, whether the slab is one-way or two-way, and the slab thickness.

Footings do not automatically need thicker bars than beams

Soil pushes up on a footing from below. An isolated footing therefore bends like an upside-down cantilever, and its main steel sits at the bottom, as a CIVILERA explainer from Bangalore describes. Robin Thomas, a former structural engineer, argues that footings carry load largely in compression, which concrete handles well. On that view, footings often need a lower steel percentage than beams or slabs. Another answer in the same thread credits ground restraint on shrinkage instead, so the reason is not settled.

On minimum steel, CIVILERA says IS 456 makes footings follow the solid-slab minimum steel rule, which it gives as 0.12%. For footings thicker than 1 m, which houses rarely need, it cites clause 34.5.2: nominal steel of 360 mm² per metre in each direction on each face. Its worked example meets that with 10 mm bars at 250 mm spacing. These figures come from a video transcript, not the code text, so confirm them with your engineer.

Footing bar diameter comes from the footing's own design moment and minimum-steel checks, not from any rule that footings outrank beams. No verified source publishes a footing bar size for a typical house, so the drawing is the only number to order against.

How to read the bar schedule on your engineer's drawing

Bar bending schedule (BBS)

the table on or with a structural drawing that lists every bar in each member by mark, diameter, number, shape, cut length and weight.

1. Match each mark to the plan. Every column, beam, footing and slab carries a mark, such as C1, B2 or F1, that ties its schedule line to a position on the plan. Count how many times each mark appears before multiplying out the steel.

2. Read diameter and count together. An entry such as "6 nos 12 mm" means six bars of 12 mm. "T8@6" c/c" means 8 mm TMT stirrups at 6-inch centre-to-centre spacing. Compare each line with the thumb rules above as a sanity check, not as grounds to change what the engineer drew.

3. Total the weight by diameter. Amrit Steels' weight chart gives 0.395 kg per metre for 8 mm, 0.617 kg for 10 mm, 0.888 kg for 12 mm and 1.58 kg for 16 mm. These figures turn cut lengths into kilograms per diameter. For whole-house totals, see how much steel a house needs.

4. Send queries to the engineer, not the dealer. Tameer Steel lists using smaller bars to save cost, and changing bar sizes without an engineer's approval, among the common mistakes that can cause cracking. The CIVIL Engineering Tutorials video that publishes the column thumb rules also tells homeowners to have the design approved by a structural engineer.

Order the whole diameter list from one supplier, by weight

An assorted diameter list is a single order that covers every diameter on the schedule, with a weight against each. If the schedule is not final yet, the Amrit Steels guide to how much steel a house needs helps estimate the total before the list is drawn up. Amrit Steels quotes from either of two things:

• the full bar bending schedule or structural drawing

• a list of diameters with the quantity of each, any brand the engineer named, and the site location

Rates are quoted for the day, because steel prices move with the market.

There is no minimum order, so the few lengths of an unusual size that a schedule sometimes calls for can go on the same list. Small quantities ship from the City Market warehouse, and large ones go direct from the company or factory to site. Delivery is the same day if the order arrives within working hours, and otherwise the next day. Loading, unloading and delivery are free on project supplies across Bangalore and its suburbs.

Everything Amrit Steels supplies is ISI-marked, and all its TMT comes as Fe 550 or Fe 550D with test reports. Order the grade and brand your engineer specifies.

Sources

1. Column Size In Building Construction: Dimensions, Types And Design Guidelines (Interior Company, 2026-06-12)

2. 8mm vs 10mm TMT Bar: Best Size for Roof Slab Construction in India - Amba Shakti Steels (Amba Shakti Steels (TMT manufacturer; competitor brand))

3. Reinforcing Steel in Footings Boosts Strength 100X - AsktheBuilder.com (AsktheBuilder.com (Tim Carter))

4. Different Steel Bar Sizes Commonly Used in Construction (Radha TMT (blog))

5. Column Size & Steel Reinforcement for 1 to 4 Storey Buildings | Avoid Mistakes & Build Safely - YouTube (CIVIL Engineering Tutorials (YouTube channel), 2024-12-10)

6. Can I use a 12mm bar for a G+2 column? - Quora (Quora answer by Ramkumar Menon)

7. Tameer SteelWhat Size Steel Reinforcement Bars Are Used in Slabs and Columns? - Tameer Steel (Tameer Steel, 2026-02-02)

8. Standard Column and Beam Sizes for G+1 | PDF | Home & Garden | Computers (Scribd user upload)

9. Can I design 8 mm bars for a main bar and distribution bars for an RCC slab of 1200 sq ft? - Quora (Quora AI assistant bot answer)

10. Is Top reinforcement needed for Isolated footings? - YouTube (CIVILERA (Bangalore), 2021-08-26)

11. Why does footing require the lowest percentage of steel among structural members beam, slab, and column? - Quora (Quora answer by Robin Thomas, former structural engineer)

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