Find out how many standard-length TMT (Thermo-Mechanically Treated) steel bars you need to order for a given total steel weight requirement.
How to Use the TMT Bar Calculator
Enter the "Total Steel Weight Required (kg)" - use the RCC Calculator to work this out from your structural element.
Enter your chosen "TMT Bar Diameter (mm)".
Enter the "Standard Bar Length (m)" your supplier sells - usually 12m.
Click "Calculate Bars Needed" to see how many bars to order.
How the Bar Count Is Worked Out
The calculator uses the D²/162 rule that site engineers and steel traders in India use to estimate the weight of round bars. It runs four steps:
Weight per metre (kg/m) = D × D ÷ 162, where D is the bar diameter in millimetres.
Weight per bar (kg) = weight per metre × standard bar length.
Number of bars = total steel weight ÷ weight per bar, rounded up to the next whole bar.
Total length = number of bars × standard bar length.
The 162 comes from the density of steel, about 7,850 kg per cubic metre. A bar 1 m long has a volume of π × D² ÷ 4 square millimetres times 1 m; multiplying by 7,850 kg/m³ and converting units gives roughly D² ÷ 162.2, which is rounded to 162.
Worked Example
Suppose your slab needs 500 kg of 12 mm bars and the dealer sells 12 m lengths. Weight per metre = 12 × 12 ÷ 162 = 0.889 kg/m. One 12 m bar weighs 0.889 × 12 = 10.67 kg. 500 ÷ 10.67 = 46.9, which rounds up to 47 bars. Those 47 bars give 564 m of steel and weigh about 501.3 kg, slightly more than the requirement because of the rounding.
Standard TMT Bar Weights (12 m Length)
Theoretical weights from the D²/162 formula for the diameters commonly stocked in India:
Diameter
Weight per metre
Weight per 12 m bar
Approx. bars per tonne
Typical use
8 mm
0.395 kg
4.74 kg
211
Stirrups, ties, lintel and slab distribution bars
10 mm
0.617 kg
7.41 kg
135
Slab main bars, light beams
12 mm
0.889 kg
10.67 kg
94
Beams, columns and footings in houses
16 mm
1.580 kg
18.96 kg
53
Columns and beams with heavier loads
20 mm
2.469 kg
29.63 kg
34
Columns, raft and pile foundations
25 mm
3.858 kg
46.30 kg
22
Large columns, multi-storey and commercial work
32 mm
6.321 kg
75.85 kg
14
Bridges and heavy infrastructure
Bars per tonne is 1,000 kg divided by the weight of one bar. Actual mill weights can differ slightly from these theoretical values within the tolerance allowed by IS 1786, so a bundle on the weighbridge may not match the count exactly.
Ordering Tips and Common Mistakes
Add wastage before you enter the weight. The calculator only rounds up to whole bars; it does not add anything for cut pieces, lap lengths or bends. Many builders add around 3 to 5 percent, but follow your engineer's bar bending schedule if you have one.
Check how the dealer bills. Steel in India is usually priced per kg or per tonne, so the weight decides the cost while the bar count decides how many pieces are delivered and cut.
Enter a different length if your supplier sells shorter bars. Some local yards sell 6 m pieces for easier transport; enter 6 to get the right count.
Match the grade on the drawing. The count does not depend on grade, but Fe 500 and Fe 550 bars are not interchangeable with Fe 415 without the designer's approval.
Frequently Asked Questions
The Steel Weight Calculator works forward - from a known diameter, length, and quantity of bars, it gives you the total weight. This TMT Bar Calculator works backward - from a known total weight requirement, it tells you how many standard bars to order.
Bars are sold as whole units, so the calculator rounds up to ensure you order enough steel to meet your weight requirement, even if the exact requirement falls partway through the last bar.
Yes - most RCC structures use different bar diameters for main reinforcement versus stirrups/distribution bars. Run this calculator separately for each diameter and its corresponding share of the total steel weight.
The D²/162 formula gives a theoretical weight. Real bars have ribs and small variations in diameter, and the Indian standard allows a mass tolerance, so a bundle can weigh a little more or less than calculated. If you pay by weight, check the weighbridge slip against the number of pieces delivered.
No. It converts the weight you enter into whole bars and nothing more. Add an allowance for laps, hooks and offcuts to the weight first, or use the figure from your bar bending schedule, which normally already includes them.