Rebar Sizes Explained (8mm to 32mm): Weight & Spacing Reference Table
Rebar is sold and specified by its diameter in millimetres — 8mm, 10mm, 12mm and up — and each size has a fixed, calculable weight per metre. This reference table covers the common sizes from 8mm to 32mm, with weight, typical uses, and the formula behind the numbers, so you can check a figure or estimate a quantity without digging through a supplier's data sheet.
The weight formula
Rebar weight per metre follows a simple formula, based on the density of steel and the bar's cross-sectional area:
where D is the bar diameter in millimetres. This is the standard approximation used across BS 8666, IS 2502 and most international rebar references, and it's the same formula this calculator uses to compute the "weight" column in your schedule automatically.
Rebar size reference table
| Size | Weight per metre | Weight per 12m length | Typical use |
|---|---|---|---|
| 6mm | 0.222 kg/m | 2.67 kg (12m length) | Fabric/mesh wire, links in light sections |
| 8mm | 0.395 kg/m | 4.74 kg (12m length) | Stirrups, links, distribution bars |
| 10mm | 0.617 kg/m | 7.41 kg (12m length) | Distribution bars, light slabs, links |
| 12mm | 0.889 kg/m | 10.67 kg (12m length) | Slab main bars, light beams, columns |
| 16mm | 1.580 kg/m | 18.96 kg (12m length) | Beam and column main bars, general structural use |
| 20mm | 2.469 kg/m | 29.63 kg (12m length) | Heavier beam and column main bars |
| 25mm | 3.858 kg/m | 46.30 kg (12m length) | Heavily loaded columns, transfer beams |
| 32mm | 6.321 kg/m | 75.85 kg (12m length) | Major structural elements, piling, transfer structures |
Choosing a rebar size
The bar size for any specific member always comes from the structural design — it depends on the load the member carries, the span, and the design code being used, not on a general size guide. That said, some patterns are common across most projects:
- Smaller bars (8–12mm) are typically used for stirrups, links, distribution steel, and lighter slabs, where the reinforcement is more about crack control and tying the structure together than carrying heavy load.
- Mid-range bars (12–20mm) cover most beam, column and structural slab main reinforcement on typical buildings.
- Larger bars (25–32mm and above) appear where loads are heavy and concentrated — transfer structures, piling, and heavily loaded columns.
Mixing bar sizes within a schedule is normal — a single beam might use 20mm main bars with 10mm stirrups, for example. What matters for the schedule is recording each size correctly against its own bar mark.
Spacing: a note of caution
Bar spacing (how far apart bars sit, centre to centre) is even more design-specific than bar size — it depends on the size and number of bars needed to satisfy the structural design, plus minimum and maximum spacing rules from the relevant design code (such as Eurocode 2 in the UK or IS 456 in India). There isn't a reliable general-purpose spacing table that applies across projects, so always take spacing from the structural drawing rather than a rule of thumb.
Turn sizes into a full schedule
Enter your bar sizes and dimensions and the calculator applies the correct weight and cutting-length formulas automatically — then export to PDF or Excel.
Open the BS 8666 calculator →Frequently asked questions
How do you calculate the weight of a rebar?
Rebar weight per metre in kilograms is calculated as the bar diameter in millimetres squared, divided by 162 (D squared over 162). Multiply this by the bar's length in metres to get its total weight.
What does 12mm rebar weigh?
A 12mm rebar weighs approximately 0.889 kg per metre, or about 10.67 kg for a standard 12-metre length.
What is the most common rebar size?
12mm and 16mm are among the most commonly used rebar sizes for general structural work such as slabs, beams and columns, though the correct size for any specific member always comes from the structural design, not a general rule of thumb.
This table is a general reference. Always follow the structural design drawing and the relevant national standard for the specific bar size, spacing and weight requirements of your project.