CostimexFree tool
Rebar Weight & Length Calculator
Calculate the total length and weight of reinforcing steel for a slab or mat — by bar diameter and centre-to-centre spacing.
Add ~5% for laps and offcuts when ordering. Doesn't include bent bars, stirrups or chairs.
Total weight
457.3 kg
= 0.457 t
Total length
515.0 m
Number of bars
77
FAQ
Common questions
How do you calculate rebar weight per metre?+
Weight (kg/m) = (diameter in mm)² × 0.006165. The tool uses the standard table: 8 mm = 0.395, 10 mm = 0.617, 12 mm = 0.888, 16 mm = 1.578, 20 mm = 2.466, 25 mm = 3.853, 32 mm = 6.313 kg/m.
How much rebar do I need for a concrete slab?+
Typical residential slabs use 10–12 mm bars at 200 mm centres both ways. The calculator returns total length and weight — add ~5% for laps and offcuts when ordering.
What's the difference between #4 rebar and 12 mm?+
US #4 bar is ⅛″ (12.7 mm) ≈ metric 13 mm — practically interchangeable with 12 mm. Use the metric size that matches your supplier's stock.
Should I include lap length in my order?+
Yes. Standard lap = 40× bar diameter (≈480 mm for 12 mm bar). Order 5–10% extra on top of the calculated length to cover laps, splices and cut waste.
Does this include stirrups or bent bars?+
No — the tool covers straight bars in a slab/mat layout. For beam stirrups, column ties or bent bars use a detailed bar bending schedule.
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