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Quick answer
At the reference density 7850 kg/m³, nominal estimates are about 0.617 kg/m for 10 mm, 0.888 for 12 mm, 1.578 for 16 mm and 2.466 for 20 mm. Use the applicable supplier or standard rate where required. Mass does not establish how much load a bar can hold.
How it works
Use the Rebar Weight Calculator South Africa to total a specified bar schedule in kilograms and metric tonnes. Add lines for different diameters, cut lengths or supplier mass rates, then keep scheduled mass, extra allowance and quoted costs separate.
Formula
Nominal kg/m = π/4 × (diameter in mm ÷ 1000)² × density in kg/m³. Scheduled kg = kg/m × cut length in metres × quantity. Add line masses, then apply any explicitly entered extra allowance.
Assumptions and common mistakes
Check units, input values and the method before relying on an estimate. Review the existing tool notes and official sources below.
Formula
Nominal kg/m = π/4 × (diameter in mm ÷ 1000)² × density in kg/m³. Scheduled kg = kg/m × cut length in metres × quantity. Add line masses, then apply any explicitly entered extra allowance.
| Step | Calculation |
|---|---|
| Nominal kg/m | π/4 × (diameter mm/1000)² × density |
| Schedule line kg | kg/m × cut length m × whole-piece count |
| Adjusted estimate | Scheduled kg × (1 + extra allowance/100) |
| Metric tonnes | Adjusted kg ÷ 1000 |
Nominal diameter reference
| Nominal diameter | Estimated kg/m | Estimated kg per 6 m piece |
|---|---|---|
| 8 mm | 0.395 | 2.368 |
| 10 mm | 0.617 | 3.699 |
| 12 mm | 0.888 | 5.327 |
| 16 mm | 1.578 | 9.470 |
| 20 mm | 2.466 | 14.797 |
| 25 mm | 3.853 | 23.120 |
| 32 mm | 6.313 | 37.880 |
Calculated at 7850 kg/m³, with rounded display values. Nominal model only, not a certified product table.
How to calculate the weight of rebar
Enter each line’s actual scheduled cut length and number of identical pieces. Choose nominal diameter with the entered reference density, or a confirmed kg/m rate. The tool converts the selected length unit to metres before multiplying. Different diameters, rates or cut lengths belong on separate lines. It totals material mass without deciding reinforcement arrangement.
Rebar weight per metre formula
For the nominal circular-area model, area is πd²/4 after converting diameter to metres. Multiply by density for kg/m. The reference 7850 kg/m³ is editable. The familiar d²/162 shortcut, with d in mm, is a rounded approximation rather than the exact coefficient used by this model. Published nominal tables, manufacturing tolerances and certified bundle mass can differ from a geometric estimate.
Y10, Y12, Y16 and Y20 references
Use the actual nominal diameter in millimetres from the specified product. The reference table below uses the stated density and rounds display values; it is not a certificate of grade or a product acceptance table. Y and T labels should be checked against the project specification and supplier identification rather than used to infer strength or interchangeable products.
Length is not diameter
A 10 m length of rebar does not specify its mass without diameter or kg/m. Conversely, 10 mm diameter does not specify the bar length. For example, a hypothetical 12 mm bar 6 m long is about 5.327 kg in the nominal model before allowance. Twenty such pieces total about 106.538 kg. Use actual scheduled cut lengths, not an assumed national stock length.
Bends, laps and cutting allowance
Cut lengths must already include the specified bends, hooks and laps from the bar schedule. The extra percentage only adds equivalent estimating length and mass; it does not generate those details or round purchases to whole stock bars. Do not add an allowance for a feature already included in the schedule. Cutting optimisation, stock lengths, bundles and supplier purchasing rules need a separate take-off.
Rebar weight calculator for slab schedules
Enter the engineer’s specified lines for each direction, layer, edge, top bar, chair or other included item with its actual cut length and count. This tool does not select diameter, spacing, cover, layers, lap length or support steel from slab dimensions. It does not calculate mesh sheets, prestressing or structural capacity from mass alone. Keep distinct schedules and omitted components visible when comparing a total.
US #4 bars and product identification
A US #4 designation does not mean 4 mm or a South African 12 mm bar. Its nominal diameter is 0.500 inch, equal to 12.7 mm. At 7850 kg/m³ this calculator’s diameter model gives about 0.994 kg/m. Check the applicable standard and unit mass before estimating or substituting. The calculator’s diameter result is a nominal model; supplier-rate mode can use the confirmed kg/m for the actual product.
Quoted costs, tonnes and Excel export
One metric tonne is 1000 kg. Optional material quotes can be per kg or per metric tonne and use the allowance-adjusted mass, with separate fabrication and delivery totals. Use one VAT basis; no extra VAT is added. Zero prices remain unpriced. Download CSV for Excel after calculating to save schedule lines and totals. The CSV is a snapshot, not a live formula workbook or certified bar-bending schedule.
How much weight can rebar hold?
Mass per metre does not determine safe load capacity. Grade, anchorage, support, member geometry, concrete, detailing and the type of loading affect structural behaviour. Obtain the required design rather than treating a heavier bar or equal total mass as proof of an acceptable substitution.
Reviewed by the 99tools team. Editorial and corrections policy.
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Frequently asked questions
How do I calculate rebar weight per metre?
Use nominal circular area × reference density, with diameter converted to metres, or enter a confirmed supplier kg/m rate.
What is Y12 rebar weight per metre?
The nominal 12 mm estimate at 7850 kg/m³ is about 0.888 kg/m. Confirm the specified product rate for procurement or certification.
What are Y16 and Y20 weights per metre?
The nominal model at 7850 kg/m³ gives about 1.578 kg/m for 16 mm and 2.466 kg/m for 20 mm.
Does 10 m rebar mean 10 mm diameter?
No. Metres describe length; millimetres here describe nominal diameter. Both length and unit mass are needed.
How much does US #4 rebar weigh?
The nominal diameter model at 7850 kg/m³ gives about 0.994 kg/m for 12.7 mm. Use the applicable product mass rate; #4 is not a 4 mm bar or an automatic 12 mm substitute.
Can this calculate slab reinforcement requirements?
It totals a specified slab bar schedule. It does not design bar spacing, diameter, layers, laps or cover.
Can I download the schedule for Excel?
Yes. CSV export includes schedule lines, kg/m, scheduled lengths and masses, allowance-adjusted masses and totals. It does not contain live workbook formulas.
Does rebar mass show safe load capacity?
No. Capacity needs a structural assessment of the complete member, material specification and detailing.
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Helpful guides
Rebar Weight per Metre: Formula and Diameters
Use nominal diameter and density or a confirmed kg/m rate to estimate reinforcing-bar mass without confusing length, bar labels and strength.
Rebar Weight Schedules for Slabs and Excel
Add specified bar lines, separate allowances from scheduled mass and export a checkable CSV quantity snapshot.