Buying Guides
How to Estimate Steel Quantities for Your Build: The Weight Chart
10 Nov 2026 · Seegaan Hardware Team · 6 min read
Order too little steel and your pour stops halfway. Order too much and you have paid for rusting stock. Estimating reinforcement steel is not guesswork — one small formula and a per-metre chart cover most of a residential build in Sri Lanka.
The only formula you need: d²/162
Every ribbed TMT bar has a standard weight per metre based on its diameter in millimetres:
Weight (kg/m) = d² ÷ 162, where d is the bar diameter in mm.
A 12 mm bar works out to 12 × 12 ÷ 162 = 0.89 kg per metre. Multiply by the total bar length and you have the steel weight for that bar size.
Ready chart: kg per metre by bar size
| Bar size | kg per metre | Common use |
|---|---|---|
| 8 mm | 0.395 | Stirrups, distribution bars |
| 10 mm | 0.617 | Slab mesh, lintels |
| 12 mm | 0.888 | Slab main bars, small columns |
| 16 mm | 1.578 | Columns, beams |
| 20 mm | 2.466 | Main columns, ground beams |
| 25 mm | 3.854 | Heavy columns, pile caps |
Rules of thumb per cubic metre of concrete
For a quick order estimate before the bar bending schedule is finalised, contractors commonly use these ranges for reinforced concrete:
- Slabs: 80–100 kg of steel per m³ of concrete
- Beams: 100–150 kg per m³
- Columns: 150–250 kg per m³
- Footings: 50–100 kg per m³
Worked example: a 5 m × 4 m roof slab at 125 mm thickness holds 2.5 m³ of concrete. At 100 kg/m³, order in the region of 250 kg of steel — typically 12 mm main bars with 8 mm stirrups and distribution bars.
Add the waste margin before you order
Bars come in 12 metre lengths and cutting always leaves offcuts. Add 5–8% for slabs and simple work, up to 10% for beams and columns with many bends. It is far cheaper than an emergency second delivery — and on a site outside Colombo, that second trip eats a half day.
FAQ
How many 12 mm bars make one tonne? One tonne ÷ 0.888 kg/m = roughly 1,127 metres of bar, or about 94 lengths of 12 m bar.
Is the d²/162 formula exact? It is the standard nominal mass used across the industry. Actual rolling tolerance per bar is small; for ordering purposes it is what suppliers quote against.
Seegaan Hardware Centre stocks TMT reinforcement steel in 8–25 mm directly imported in Colombo, delivered island-wide. Send your bar schedule for a quote via the contact page or WhatsApp +94 71 476 8409.
AI-generated (Flux via Writeseed), 2026-11-10
