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

0.8874 kilograms per metre, from 12² ÷ 162.28. A standard 12 metre bar therefore weighs about 10.65 kilograms.

Why is the constant 162 and not 165?

It derives from the density of steel and the geometry of a circular section: 7,850 × π ÷ 4,000,000 gives 1 ÷ 162.28. Values other than this are rounding conventions rather than different physics.

Does this calculator design the reinforcement?

No. Bar diameter, spacing, lap length and layout are structural design outputs that must come from a qualified structural engineer. This calculator converts a schedule you already have into weight.

Where does the d²/162 formula come from?

It is the weight of a steel bar of diameter d in millimetres, derived from the cross-sectional area and a density of about 7,850 kg per cubic metre. It converts diameter and length into weight and nothing else. It carries no information about grade, spacing, laps or whether the reinforcement is adequate.

Steel weight calculator — TMT bar weight per metre and total tonnage

Convert bar diameter, length and count into kilograms and tonnes using the d²/162 unit-weight rule, with a wastage and lap allowance you set.

Bar

Bar diameteryou enter

Take this from your structural drawings and specification. DevPartner does not specify mixes, grades or reinforcement.

Length per baryou enter

Number of barsyou enter

Ordering

Laps, cutting and wastageyou enter

Lap lengths are a design requirement and can add materially to tonnage. Take the allowance from your bar bending schedule.

Result — calculated from your inputs

Total weight532.44 kg

With laps and wastage559.06 kg

In tonnes0.5591 t

Working

Unit weight of 12 mm bar0.8874 kg / m

Total bar length600.00 m

Net weight532.44 kg

Allowance26.62 kg

Order weight559.06 kg

Common bar unit weights

8 mm0.3944 kg / m

10 mm0.6162 kg / m

12 mm0.8874 kg / m

16 mm1.5775 kg / m

20 mm2.4649 kg / m

25 mm3.8514 kg / m

32 mm6.3101 kg / m

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Nothing from this calculator maps into the assessment intake, so you will start from a blank site. No opportunity is created until you save one.

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How this calculator works

unit weight (kg/m) = d² ÷ 162.28      where d is diameter in mm
total weight       = unit weight × length × number of bars
order weight       = total weight × (1 + allowance %)

The constant 162.28 comes from steel density 7850 kg/m³ applied to a circular section.

You enter: A value you supply. Nothing is assumed for you.
Calculated: Arithmetic on your inputs, shown in the working.
Assumption: A factor or allowance you can change — mix ratios, wastage, dry-volume factors.
Approximation: Geometry or method that approximates reality; labelled wherever used.
Verify locally: Planning parameters, statutory rates and structural design must come from the authority or a qualified professional.

Where d squared over 162 comes from

The cross-sectional area of a round bar is πd²/4. In square metres with d in millimetres that is πd²/4,000,000. Multiplying by the density of steel, 7,850 kilograms per cubic metre, gives 7,850πd²/4,000,000, which simplifies to d²/162.28 kilograms per metre. The rule is exact arithmetic, not a rule of thumb.

Many site references round the constant to 162, which overstates weight by about 0.17 percent. This calculator uses 162.28 so that a tonnage figure reconciles against a mill test certificate.

Laps are not wastage

Lap lengths, development lengths, hooks and bends are design requirements that add real steel to the structure, and on a heavily reinforced frame they can add five to ten percent or more to the theoretical bar length. Cutting waste is separate and smaller.

The right source for both is a bar bending schedule prepared from the structural drawings. Where you do not yet have one, use this calculator for order-of-magnitude checking only, and treat the result as indicative.

Worked example

Ten 12 mm bars at 12 m each is 120 m of bar. At d²/162 the unit weight is 0.888 kg per metre, so the lot weighs about 106.6 kg. Add a row of 16 mm bars at 1.578 kg per metre and the tonnage builds up row by row.

At 3% wastage for cutting and laps the order weight rises to about 110 kg for the 12 mm row alone.

Mistakes in steel take-off

Measuring member length instead of bar length, which excludes laps, bends, hooks and development length and understates the order every time.

Rounding the unit weight to two decimals early and multiplying it across a tonnage.

Ordering to the calculated weight with no allowance for cutting waste and standard stock lengths.

This is quantity only, not design

The d²/162 relationship is a density conversion, nothing more. Bar diameter, spacing, grade, laps, cover and curtailment are decided by a qualified structural engineer against the design of the specific building.

Never take a bar size or a quantity from this page into construction. Use the engineer's bar bending schedule.

Frequently asked questions

What is the weight of a 12 mm TMT bar per metre?: 0.8874 kilograms per metre, from 12² ÷ 162.28. A standard 12 metre bar therefore weighs about 10.65 kilograms.
Why is the constant 162 and not 165?: It derives from the density of steel and the geometry of a circular section: 7,850 × π ÷ 4,000,000 gives 1 ÷ 162.28. Values other than this are rounding conventions rather than different physics.
Does this calculator design the reinforcement?: No. Bar diameter, spacing, lap length and layout are structural design outputs that must come from a qualified structural engineer. This calculator converts a schedule you already have into weight.
Where does the d²/162 formula come from?: It is the weight of a steel bar of diameter d in millimetres, derived from the cross-sectional area and a density of about 7,850 kg per cubic metre. It converts diameter and length into weight and nothing else. It carries no information about grade, spacing, laps or whether the reinforcement is adequate.