117 rebar cells — a 6 m D13 bar weighs 5.97 kg
Every pairing of 13 bar sizes and 9 lengths, worked out as kilograms. There is no table to memorise — the nominal diameter fixes the cross-section, multiplying that by the density of steel, 7850 kg/m³, gives the weight per metre, and length times count gives the total.
The weight per metre comes out of the density
Rebar is a long bar with a round cross-section, so the volume of one metre is fixed, and its weight is that volume times the density of steel, 7850 kg/m³. The weight per metre is therefore π/4 × diameter² × 7850 ÷ 10⁶, and the 0.006165 × diameter² shortcut used on site is nothing but that formula tidied up. Knowing where the number came from beats memorising it: any diameter can be worked out without a table.
D13 is a name, 12.7 mm is the diameter
The 13 in D13 is a label; the diameter that goes into the formula is 12.7 mm, inherited from a half inch. Feed the label into the formula and you get 1.042 kg/m, 5 % heavier than the standard value of 0.995 kg/m. The same choice is why a ribbed bar can be treated as a smooth cylinder at all: the standard sets the nominal diameter so that it reproduces the real mass.
Length times count is the total
Once the weight per metre is known, the rest is multiplication. A 6 m D13 bar is 0.995 × 6 = 5.97 kg, a hundred of them come to 597 kg, and a tonne holds 167 bars. Run it backwards — delivered weight divided by the weight per metre — and you get total length, so a weighbridge alone can check what arrived.
Ordered tonnage adds splices and waste
Lengths taken off a drawing are net. Every lap splice adds about 40 diameters — 0.508 m for a D13 — and offcuts push the order 3 to 5 % higher. Each cell here also lists the weight with 5 % waste added. Forty diameters is a rule of thumb: the real lap length is set by the drawing, following the concrete strength and the steel grade.
At a glance
Weight per bar
D6⌀ 6.35 mm · 0.249 kg/m
D10⌀ 9.53 mm · 0.56 kg/m
D13⌀ 12.7 mm · 0.995 kg/m
D16⌀ 15.9 mm · 1.56 kg/m
D19⌀ 19.1 mm · 2.25 kg/m
D22⌀ 22.2 mm · 3.04 kg/m
D25⌀ 25.4 mm · 3.98 kg/m
D29⌀ 28.6 mm · 5.04 kg/m
D32⌀ 31.8 mm · 6.23 kg/m
D35⌀ 34.9 mm · 7.51 kg/m
D38⌀ 38.1 mm · 8.95 kg/m
D41⌀ 41.3 mm · 10.5 kg/m
D51⌀ 50.8 mm · 15.9 kg/m
Worth knowing
- Weight per metre (kg/m) is π/4 × nominal diameter² × 7850 ÷ 10⁶ — that is the 0.006165 factor.
- What goes into the formula is the nominal diameter, not the label: D13 means 12.7 mm.
- Total weight is weight per metre × length × count, and doubling the diameter quadruples the weight.
- An order adds lap splices, roughly 40 diameters each, and 3 to 5 % for waste.
Common questions
Q. How do I work out the weight per metre?
π/4 × nominal diameter² × 7850 ÷ 10⁶. Tidied up that is 0.006165 × diameter², which gives 0.995 kg/m for a D13 at 12.7 mm. The factor is just the density of steel, 7850 kg/m³, and π — nothing to memorise.
Q. Is a D13 bar 13 mm across?
No. The 13 is a label; the nominal diameter is 12.7 mm. Putting 13 into the formula returns 1.042 kg/m, about 5 % above the standard value.
Q. Can I order straight off the lengths on the drawing?
Add splices and waste first. Each lap splice runs about 40 diameters — 0.508 m for a D13 — and offcuts add another 3 to 5 %.