Unit Weight of Steel Bars: D²/162 Formula, Weight Chart (6–40 mm) & Examples

On every site, someone asks the same question: how many kg is this bar? You need it to check the steel delivered by the supplier, to make the bar bending schedule, and to work out the cost. The answer is one short formula: W = D²/162. This guide explains where the formula comes from, gives a ready steel weight chart for 6 mm to 40 mm bars (per metre, per foot and per 12 m bar), and shows worked examples you can copy on site.

The formula: W = D²/162

Weight of steel bar (kg per metre) = D² ÷ 162, where D is the bar diameter in millimetres.

Example: a 12 mm bar weighs 12 × 12 ÷ 162 = 144 ÷ 162 = 0.888 kg per metre.

If you want the weight of a full length, multiply by the length in metres:

Total weight (kg) = (D² ÷ 162) × L, where L is the length in metres.

Where does D²/162 come from?

It is just volume × density for a 1 metre long round bar.

1. Density of steel = 7,850 kg/m³.
2. Cross-section area of a bar = πD²/4. With D in mm, the area in m² is πD²/4 × 10⁻⁶.
3. Volume of 1 m length = area × 1 m = πD²/4 × 10⁻⁶ m³.
4. Weight of 1 m = 7,850 × π/4 × 10⁻⁶ × D² = 0.006165 × D² kg.
5. 1 ÷ 0.006165 = 162.2, so the weight is D²/162.2. On site we round it to D²/162.

So the formula is not a thumb rule. It is exact for a plain round bar with a density of 7,850 kg/m³. Ribbed TMT bars are sold by nominal diameter, and their nominal mass per metre in IS 1786 matches this formula.

Steel weight chart (6 mm to 40 mm)

Bookmark this table. The 12 m column is useful because TMT bars are normally supplied in 12 m lengths.

Bar dia (mm)	Weight (kg/m)	Weight (kg/ft)	One 12 m bar (kg)	Bars per tonne (12 m)
6	0.222	0.068	2.66	375
8	0.395	0.120	4.74	210
10	0.617	0.188	7.40	135
12	0.888	0.271	10.66	93
16	1.580	0.482	18.96	52
20	2.470	0.753	29.64	33
25	3.850	1.173	46.20	21
28	4.830	1.472	57.96	17
32	6.310	1.923	75.72	13
36	7.990	2.435	95.88	10
40	9.860	3.005	118.32	8

Easy way to remember: the 10 mm bar is about 0.62 kg/m, and every other size is that number × (D/10)². For example, 20 mm is 4 times 10 mm: 0.617 × 4 = 2.47 kg/m.

Weight per foot: D²/533

Many sites in India still measure in feet. Since 1 m = 3.2808 ft, the per-foot formula is D²/533 (D in mm, answer in kg per foot). Example: 16 mm bar = 256 ÷ 533 = 0.48 kg/ft.

Worked examples

Example 1: Main bars of a beam

A beam has 4 bars of 16 mm, each 5.2 m long (including bends and anchorage).

• Total length = 4 × 5.2 = 20.8 m
• Weight per metre = 16² ÷ 162 = 1.58 kg/m
• Total weight = 20.8 × 1.58 = 32.9 kg

Example 2: Stirrups

The same beam has 32 stirrups of 8 mm. Cutting length of one stirrup = 1.10 m.

• Total length = 32 × 1.10 = 35.2 m
• Weight = 35.2 × 0.395 = 13.9 kg

Total steel in the beam = 32.9 + 13.9 = 46.8 kg. This is exactly how a bar bending schedule (BBS) is totalled: length of each bar type × unit weight.

Example 3: Checking a delivery

The supplier delivers a bundle of 12 mm bars and says it is 1 tonne. You count 90 bars of 12 m.

• Theoretical weight = 90 × 10.66 = 959 kg
• The bill says 1,000 kg. The difference is 41 kg, which is 4.1% less steel than billed.

Now weigh a few sample bars. If they really weigh about 11.1 kg each, the bars are heavier than nominal and the bill is fair. If they weigh 10.66 kg, you are being billed for 41 kg you did not receive. See the next section for the allowed tolerance.

Weight tolerance for TMT bars

Real bars are never exactly the nominal weight. IS 1786 allows a small variation in mass per metre. The commonly quoted batch tolerances are:

Nominal size	Allowed variation (batch)
Up to and including 10 mm	± 7%
Over 10 mm up to 16 mm	± 5%
Over 16 mm	± 3%

Site tip: cut a 1 m piece from 2–3 random bars, weigh them on a good scale, and compare with the chart. A bar that is much lighter than the tolerance is thinner than its nominal size, which means less area of steel than the design assumes.

Bars vs bill: buying by weight or by count

• Actual weight (weighbridge): you pay for what the truck really carries. Best for large orders.
• Theoretical weight (count × chart): you pay for bars × nominal weight. Fair if the bars are within tolerance.

Either way, write the number of bars of each size on the delivery challan. It is the easiest record to check later.

Weight of steel plates, sections and pipes

The same idea (volume × 7,850) works for any steel shape:

• Steel plate: 7.85 kg per m² for every 1 mm of thickness. A 10 mm plate of 1.5 m × 1 m = 1.5 × 10 × 7.85 = 117.8 kg.
• Square bar (side a mm): a² × 0.00785 kg/m. A 20 mm square bar = 3.14 kg/m.
• Pipe (outer dia D, thickness t, both in mm): 0.02466 × t × (D − t) kg/m.

How much steel does a building need?

For an early budget, engineers use steel per sq ft of built-up area. A normal residential RCC building uses about 3.5 to 4.5 kg of steel per sq ft, depending on height, spans and seismic zone. For the full material list (cement, sand, aggregate, bricks), use our free building estimate Excel sheet. For the detailed quantity, prepare a BBS from the drawings and use the chart above.

Common mistakes

• Using D in cm or inches. The formula needs D in millimetres.
• Forgetting laps, bends and hooks. Always use the cutting length, not the clear length between supports. Laps alone can add 5–10% to the steel quantity.
• No wastage allowance. Add about 3–5% for cutting waste when you order.
• Mixing up diameter. Measure ribbed bars across the core, or better, check weight per metre. A worn caliper on the ribs will over-read.

Frequently asked questions

What is the weight of a 12 mm steel bar per metre?

0.888 kg per metre (12² ÷ 162). One 12 m length weighs about 10.66 kg.

What is the weight of a 10 mm bar of 12 m length?

0.617 kg/m × 12 m = 7.40 kg.

Why 162?

Because 7,850 × π/4 × 10⁻⁶ = 1/162.2. It comes from the density of steel and the area of a circle.

Does the formula work for Fe 500 and Fe 550D bars?

Yes. The grade changes the strength, not the density. A 16 mm Fe 415, Fe 500 or Fe 550D bar all weigh about 1.58 kg/m. Read more on rebar types and grades.

How many 8 mm bars are in 1 tonne?

About 210 bars of 12 m length (1,000 ÷ 4.74).

Summary

• Weight of steel bar = D²/162 kg per metre (D in mm).
• Per foot, use D²/533.
• Multiply by the total cutting length to get kg, then add 3–5% wastage when ordering.
• Check deliveries by counting bars and weighing a few 1 m samples.