Steel Bar Weight Chart (6mm–40mm) with Formula d²/162.2
On every reinforcement estimate — a bar bending schedule, a material order, a site reconciliation — the same number is used over and over: the weight of one metre of steel bar of a given diameter. Every site engineer eventually memorises the common ones (10 mm = 0.617 kg/m, 12 mm = 0.888 kg/m), but the formula behind them is worth understanding, because it lets you compute any diameter in seconds and catch errors in a schedule.
This article derives the formula step by step, gives the complete chart from 6 mm to 40 mm, and works through practical site examples.
Deriving the Formula
Weight is volume multiplied by density. For a round steel bar:
W = cross-sectional area × length × density of steel
where:
- A = cross-sectional area = π/4 × d²
- d = bar diameter
- L = bar length
- ρ = density of steel = 7850 kg/m³
So:
W = (π/4) × d² × L × 7850
The units need care. Bar diameter is measured in millimetres, while density is in kg per cubic metre. To keep the units consistent, convert the diameter from millimetres to metres:
1 mm = 1/1000 m, so d² in mm² becomes d²/1000² in m².
Substituting with π = 3.1416:
W = [3.1416 × d² / (4 × 1000 × 1000)] × L × 7850
W = d² × L × (3.1416 × 7850 / 4,000,000)
W = d² × L × 0.006165
W = d²L / 162.2 kg
where d is in millimetres and L is in metres.
Set L = 1 metre and you get the unit weight — weight per metre run:
Unit weight (kg/m) = d² / 162.2
Some references round the denominator to 162. The difference is tiny (about 0.1%), and both are acceptable for site work. The values in the chart below use 162.2.
Steel Bar Weight Chart (kg/m)
| Bar diameter (mm) | Calculation | Unit weight (kg/m) |
|---|---|---|
| 6 | 6² / 162.2 | 0.222 |
| 8 | 8² / 162.2 | 0.395 |
| 10 | 10² / 162.2 | 0.617 |
| 12 | 12² / 162.2 | 0.888 |
| 16 | 16² / 162.2 | 1.578 |
| 20 | 20² / 162.2 | 2.466 |
| 25 | 25² / 162.2 | 3.853 |
| 28 | 28² / 162.2 | 4.834 |
| 32 | 32² / 162.2 | 6.313 |
| 36 | 36² / 162.2 | 7.990 |
| 40 | 40² / 162.2 | 9.865 |
A few observations worth remembering:
- 8, 10, 12, 16, 20, 25 mm are the everyday diameters on building sites — these six are worth memorising.
- Doubling the diameter quadruples the weight (weight grows with d²). A 20 mm bar is four times heavier per metre than a 10 mm bar, not twice.
- Bars are normally supplied in 12 m lengths (about 40 ft) in Pakistan, so the weight of a full standard bar is simply 12 times the unit weight — e.g. one 16 mm bar ≈ 18.9 kg.
Worked Examples
Example 1 — Weight of 12 m of 16 mm bar
A beam needs a single 16 mm bar, 12 m long (a standard bar length).
Unit weight of 16 mm bar = 16² / 162.2 = 1.578 kg/m
Weight = 12 × 1.578 = 18.94 kg ≈ 19 kg
Example 2 — Total weight of 85 bars of 12 mm × 12 m
A footing requires 85 bars of 12 mm diameter, each 12 m long.
Total length = 85 × 12 = 1020 m
Unit weight of 12 mm bar = 12² / 162.2 = 0.888 kg/m
Total weight = 1020 × 0.888 = 905.76 kg ≈ 906 kg (0.91 tonnes)
Example 3 — Converting a bar bending schedule to tonnage
Suppose the BBS gives the following total cut lengths:
| Bar dia (mm) | Total length (m) | Unit weight (kg/m) | Weight (kg) |
|---|---|---|---|
| 10 | 1,240 | 0.617 | 765.1 |
| 12 | 3,860 | 0.888 | 3,427.7 |
| 16 | 2,150 | 1.578 | 3,392.7 |
| 20 | 940 | 2.466 | 2,318.0 |
| Total | 9,903.5 kg ≈ 9.90 t |
Add the usual cutting waste allowance (2–5% depending on the project) on top of the tonnage before ordering.
Example 4 — Quick mental check on site
The storekeeper reports receiving 50 bars of 25 mm steel. Each bar is 12 m.
Weight per bar = 12 × 3.853 = 46.2 kg
Total = 50 × 46.2 = 2,310 kg ≈ 2.31 t
Compare this against the delivery challan before unloading. A mismatch often points to a wrong diameter being delivered — a serious problem that is cheap to catch at the gate.
Practical Notes for Site Work
- Check the diameter, not just the weight. Weighing a bundle is a rough check, but measuring the bar diameter with a caliper is the reliable one — an undersized bar changes the steel area, which is a structural issue, not just a weight issue.
- Tolerances exist. Mill-rolled bars have small rolling tolerances on diameter and weight (typically ±4–8% on weight per national standards). A small deviation from the chart is normal; a large one is not.
- Don’t mix units. The most common error is entering the diameter in centimetres or the length in feet into d²L/162.2. Millimetres and metres only. If you work in feet, the equivalent constant is d²L/533 (d in mm, L in feet).
- Lap lengths add steel. A BBS that ignores lap lengths under-reports tonnage. Make sure laps, hooks, and bends are in the schedule before converting to weight.
Steel Weight Calculator
Calculate weight of steel bars
Weight of a Full 12 m Standard Bar
On site you rarely handle one metre of steel — you handle full 12 m bars. This table gives the weight of one standard bar per diameter, the number you actually lift, load, and count:
| Bar diameter (mm) | kg/m | Weight of 12 m bar (kg) |
|---|---|---|
| 6 | 0.222 | 2.66 |
| 8 | 0.395 | 4.74 |
| 10 | 0.617 | 7.40 |
| 12 | 0.888 | 10.66 |
| 16 | 1.578 | 18.94 |
| 20 | 2.466 | 29.59 |
| 25 | 3.853 | 46.24 |
| 28 | 4.834 | 58.01 |
| 32 | 6.313 | 75.76 |
| 36 | 7.990 | 95.88 |
| 40 | 9.865 | 118.38 |
Practical note: A bundle of twenty 12 mm bars weighs over 210 kg — that is why bundles are crane-lifted, and why a missing bundle on the challan is real money.
How Many Bars Make One Tonne?
The reverse question comes up at every material order. Number of 12 m bars per 1000 kg:
| Bar diameter (mm) | Bars per tonne (12 m each) |
|---|---|
| 8 | ~211 |
| 10 | ~135 |
| 12 | ~94 |
| 16 | ~53 |
| 20 | ~34 |
| 25 | ~22 |
| 32 | ~13 |
So “2 tonnes of 12 mm steel” means roughly 188 bars — count them at the gate. I have seen deliveries short by 8–10 bars hidden inside a plausible-looking total weight; counting bars per diameter is the check that catches it.
Worked Example 5 — Gate Reconciliation Dispute
The delivery challan says 2.50 tonnes of 16 mm bars. You count 130 bars at the gate, each 12 m.
Expected weight = 130 × 18.94 = 2,462 kg = 2.46 t
Shortfall = 2.50 − 2.46 = 0.04 t (40 kg) — about 1.6%, inside normal rolling tolerance. Accept the delivery, but note the count on the challan.
Now suppose you had counted only 118 bars: 118 × 18.94 = 2,235 kg — a 265 kg shortfall (over 10%). That is not tolerance; that is a short delivery or a wrong diameter mixed in. Hold the truck, measure bar diameters with a caliper, and call the supplier before unloading. This ten-minute check at the gate has saved more project money than any laboratory test I know.
More Questions Site Engineers Ask
What is the weight of 8 mm bar per metre? 0.395 kg/m (8²/162.2). A 12 m bar weighs about 4.74 kg.
How many 12 mm bars are in 1 ton? About 94 bars of 12 m length (1000 ÷ 10.66). For ordering, say 94–95 bars per tonne.
Is there a weight difference between TMT and TOR steel? No, for practical purposes. Both use the same steel density (7850 kg/m³), so the d²/162.2 formula applies identically. The strength grades differ (Fe415, Fe500, Fe550/600), not the weight.
Why do some charts use 162 and others 162.2? 162.2 is the exact value from (π/4) × 7850 with unit conversion; 162 is the rounded shortcut. The difference is about 0.1% — roughly 1 kg per tonne. Either is fine for site work; just be consistent within one estimate.
What weight tolerance is acceptable on delivered steel? National standards typically allow ±4–8% on the weight of a bar lot (rolling tolerance). Within that band, accept. Beyond it — especially combined with a low bar count — measure diameters and dispute the delivery.
Frequently Asked Questions
What is the unit weight of a 12 mm steel bar? 0.888 kg/m. A standard 12 m bar therefore weighs about 10.66 kg.
Why is the formula d²/162? It comes from (π/4) × 7850 kg/m³ converted to work with diameter in millimetres and length in metres. The exact denominator is 162.2; 162 is the common rounded value.
What is the weight of 1 m of 20 mm bar? 20² / 162.2 = 2.466 kg/m.
Does the formula apply to all steel, including TMT bars? Yes, for weight purposes. TMT, tor, and plain mild steel bars all use the same density (7850 kg/m³), so the formula applies to all of them. The rib pattern on deformed bars is accounted for in the nominal diameter.
Final Thoughts
The steel bar weight formula is one of those small tools that separates engineers who estimate confidently from those who guess. Memorise the six common values, keep the d²/162.2 derivation in mind for everything else, and always reconcile delivered steel against the challan at the gate — it is the cheapest quality check on the whole site.
Written by Mohsin Raza Adil — BSc Civil Engineering Technologist (NTC-registered), Pakistan.
Mohsin Raza Adil
BSc Civil Engineering Technologist (NTC-registered), Pakistan. I write practical, field-tested guides on construction materials, soil testing and site engineering — the way it is actually done on site.
