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

A 12 mm reinforcement bar weighs about 0.888 kg per metre, so a standard 12 m bar is roughly 10.65 kg. The figure comes from the formula weight = d²/162.28, where d is the diameter in millimetres: 12² / 162.28 = 0.887 kg/m. The density-based value (7850 kg/m³) is 0.8878 kg/m — the same to three decimals.

How do you calculate the weight of a steel bar?

Multiply the unit weight by the length. Unit weight in kg per metre is d²/162.28 (d in mm), derived from steel density 7850 kg/m³ and a circular cross-section. For example, 300 m of 10 mm bar: unit weight 100/162.28 = 0.616 kg/m, so 0.616 × 300 = 184.9 kg.

How many kg is one 12mm steel bar in Sri Lanka?

A single 12 mm bar in the standard 12 m length weighs about 10.65 kg (0.888 kg/m × 12 m). Sold-per-kg, at Rs 320/kg that one bar costs roughly Rs 3,410. Note that some suppliers stock 40 ft (≈ 12.2 m) bars, which are slightly heavier — set the standard length field to match your supplier.

What are the standard reinforcement bar sizes used in Sri Lanka?

Sri Lankan hardware stores stock eight nominal sizes: 6, 8, 10, 12, 16, 20, 25 and 32 mm, per SLS 375 / BS 4449. Mild round bars are labelled R (e.g. R6, R10) and deformed high-tensile bars are labelled T or Tor (e.g. T12, T16). The weight per metre is the same for a given diameter regardless of the R/T grade.

Why is steel sold by weight but drawings specify length?

Engineers detail bar-bending schedules in lengths and spacing (for example "T12 @ 150 c/c"), because that is what defines the structure. Suppliers price by weight because that reflects the raw steel used. This calculator bridges the two: enter the length or piece count from the drawing and it returns the kilograms and rupees you'll pay at the counter.

Should I add a wastage or lap allowance?

Yes, usually. Bars are cut, lapped and offcut on site, so the steel you buy exceeds the net length on the drawing. A 3–5% allowance is common for slabs and beams; congested columns or heavy lapping can reach 8–10%. Enter your figure in the wastage field and it is applied to both the weight and the bars-to-order count.

How much steel is needed for a concrete slab?

It depends entirely on the engineer's design — bar size, spacing, and slab area. As a rough order of magnitude, house slabs often use 60–90 kg of steel per cubic metre of concrete, but always follow the structural drawing. This tool weighs and costs the exact bars specified; it does not design the reinforcement.

Does the calculator use live steel prices?

No. Steel prices in Sri Lanka move daily and vary by brand (Melwa, Lanwa, Ceylon Steel) and shop, so the tool never guesses. You enter your own price per kilogram from a quotation, and it costs the whole bill at that rate. Leave the price blank to get weights and bar counts only.

When was the weight table last verified?

The unit-weight table was last reconciled against the SLS 375 / BS 4449 nominal-mass values on 2026-07-11. Because it rests on fixed physical constants (steel density and geometry) rather than changing rates, it does not need frequent updates — only the price you enter changes over time.

Sri Lanka · Construction

Sri Lanka Steel Bar Weight & Cost Calculator

Turn metres of reinforcement bar into kilograms, the number of standard bars to order, and rupees — for a single size or a whole slab schedule. Uses the SLS 375 / BS 4449 d²/162.28 formula. No signup, sources cited.

By Induwara Ashinsana— Executive Director, Ryzera TechnologiesUpdated Jul 11, 2026

Steel bar weight & costSLS 375 / BS 4449

d² / 162.28 verified

Bar 112 mm = 0.888 kg/m

Bar size

pcs

Standard bar length (m)

Bars are stocked in 12 m lengths in SL.

Price per kg (Rs)

Enter your hardware-shop rate to cost the bill.

Wastage / lap (%)

Extra for laps and offcuts. Typical 3–5%.

Total weight

266.34 kg

Bars to order

At 12 m per bar

Total length

300 m

Per-size breakdown

Size	kg/m	Length	Weight	Bars
12 mm	0.888	300 m	266.34 kg	25
Total	—	300 m	266.34 kg	25

Weights use steel density 7850 kg/m³ (W = d²/162.28 kg/m), per SLS 375 / BS 4449. Prices are your own input — no live feed.

How it works

Reinforcement steel in Sri Lanka is sold by weight (per kilogram), but engineers' drawings and bar-bending schedules specify lengths and spacing. This calculator bridges the gap using one physical constant and a bit of geometry, so the answer is exact rather than a guess.

The weight of a round bar per metre depends only on its cross-sectional area and the density of steel. For a nominal diameter d in millimetres and steel density 7850 kg/m³ (the BS/ISO value for reinforcement steel):

W = 7850 × (π / 4) × (d / 1000)² → simplifies to W ≈ d² / 162.28 (kg/m)

Both forms agree to within about 0.1%. The tool uses the density-based value internally and exposes the familiar d²/162.28 rule as a cross-check — the badge on the calculator card reflects that the two methods match the SLS 375 / BS 4449 nominal-mass table. From the unit weight, the rest is arithmetic:

Total length per size. If you enter a total length, that is used directly. If you enter pieces × length, they are multiplied together.
Wastage. The length is multiplied by (1 + wastage% / 100) to allow for laps and offcuts, if you set one.
Weight.Effective length × the size's kg/m gives the weight in kilograms.
Bars to order. Effective length ÷ standard bar length (12 m by default), rounded up, because you buy whole bars.
Cost. Weight × your price per kilogram, summed across all sizes for a grand total. Prices are your own input — the tool never scrapes a live feed, because rates change daily and vary by brand and shop.

Every size you add is priced separately in the per-size breakdown and then combined, so you can hand the totals straight to a hardware supplier. The eight nominal sizes (6, 8, 10, 12, 16, 20, 25, 32 mm) are the diameters actually stocked in Sri Lanka.

Worked examples

Single size with cost — 25 × T12 at Rs 320/kg

Unit weight: 12² / 162.28 = 0.888 kg/m
Total length: 25 pieces × 12 m = 300 m
Weight: 0.888 × 300 = 266.3 kg
Bars to order: ceil(300 / 12) = 25 bars
Cost: 266.3 × Rs 320 = Rs 85,230

Mixed slab schedule, no price — 300 m T10 + 150 m T16

T10: 100 / 162.28 = 0.616 kg/m → 0.616 × 300 = 184.9 kg; bars = ceil(300/12) = 25
T16: 256 / 162.28 = 1.578 kg/m → 1.578 × 150 = 236.8 kg; bars = ceil(150/12) = 13
Combined weight: 184.9 + 236.8 = 421.7 kg
Combined bars: 25 + 13 = 38 standard bars

With 10% wastage — 120 m of T16, 12 m bars

Effective length: 120 × 1.10 = 132 m
Weight: 1.578 × 132 = 208.3 kg
Bars to order: ceil(132 / 12) = 11 bars (exactly, no rounding up)
The wastage lifts both the weight and the bar count so nothing runs short on site.

Standard bar sizes reference

The weight per metre and per standard 12 m bar for every nominal size stocked in Sri Lanka, computed from the same formula the calculator uses:

Nominal size	Weight per metre	Weight per 12 m bar
6 mm	0.222 kg/m	2.66 kg
8 mm	0.395 kg/m	4.74 kg
10 mm	0.617 kg/m	7.40 kg
12 mm	0.888 kg/m	10.65 kg
16 mm	1.578 kg/m	18.94 kg
20 mm	2.466 kg/m	29.59 kg
25 mm	3.853 kg/m	46.24 kg
32 mm	6.313 kg/m	75.76 kg

Frequently asked questions

Sources & references

The unit-weight table rests on steel density 7850 kg/m³ and the circular cross-section formula, cross-checked against the SLS 375 / BS 4449 nominal-mass values on 2026-07-11. Prices are entered by you and are not part of this table.

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