Steel Calculator for Construction
Bar weight by diameter with the D x D / 162 rule, plus a thumb-rule reinforcement estimate from concrete volume.
1. Bar weight by diameter
| Bar dia (mm) | kg per metre | Number of bars | Length per bar (m) | Weight (kg) |
|---|
2. Thumb-rule estimate from concrete volume
How the steel calculation is done
The weight of a round bar per metre is its diameter squared divided by 162, with the diameter in millimetres and the answer in kilograms. The 162 comes from the density of steel (7,850 kg per cu m) and the area of a circle. So an 8 mm bar weighs 0.395 kg per metre, 12 mm weighs 0.888, 16 mm weighs 1.58 and 25 mm weighs 3.86. Multiply by the number of bars and the length of each to get the total, and divide by 1,000 for tonnes.
The second part uses thumb rules that site engineers use before the bar bending schedule is ready: roughly 80 kg of steel per cu m of concrete in footings and slabs, 150 kg in beams and 200 kg in columns. These are typical for residential RCC frames in India and can be edited for the job.
Worked example (default inputs)
Ten bars of 12 mm, 12 m long: 0.888 x 10 x 12 = 106.6 kg. Thumb rule: footing 10 cu m x 80 = 800 kg, column 8 x 200 = 1,600 kg, beam 12 x 150 = 1,800 kg, slab 30 x 80 = 2,400 kg; total 6,600 kg, and 6,798 kg (6.8 t) with 3% for wastage and laps.
How many 12 mm bars are in one tonne?
A 12 m bar of 12 mm weighs 10.66 kg, so a tonne holds about 94 bars. For 8 mm it is about 211 bars, for 16 mm about 53 and for 20 mm about 34.
Is the thumb rule enough to order steel?
It is enough to budget and to place the first indent so work does not stop. Order the balance from the bar bending schedule, which also tells you the cutting lengths and the number of pieces per diameter.
How much steel wastage should I allow?
Two to three percent for cutting and laps on a well-planned site; up to five percent where bar lengths are not planned against the standard 12 m bar.
Once the steel is ordered, the delivery, the diameter-wise stock and the consumption per pour can be recorded on the phone so the thumb-rule estimate is checked against what was actually used: track material and labour in Trackovo. Trackovo is a construction site management app with material, labour attendance, DPR and payments, with a 14-day free trial.