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Rebar Weight Calculator

Rebar weight per metre = D² ÷ 162, where D is the bar diameter in mm. A 12 mm bar weighs 12² ÷ 162 = 0.888 kg/m, so a 12 m length weighs about 10.65 kg. Multiply by total length for the full weight; for US bars use the ASTM lb/ft value.

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Total weight
10.65kg
In tonnes0.011 t
Unit weight0.888 kg/m
Total length12.00 m
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Working
  1. Unit weight = D² ÷ 162 = 12² ÷ 162 = 0.889 kg/m (rule of thumb)
  2. Exact: π/4 × D² × 7,850 kg/m³ = 0.888 kg/m
  3. Total length = 12.00 m × 1 = 12.00 m
  4. Weight = 0.888 × 12.00 = 10.65 kg
Results are estimates for planning and material ordering only. They are not a substitute for structural design or approval by a qualified engineer. Read the full disclaimer.
Formula


Unit weight (kg/m) = D² ÷ 162          (D in mm: the site rule)
Exact:               π/4 × D² × 7,850 ÷ 1,000,000
Total weight (kg)  = Unit weight × Bar length × Number of bars


D²/162 is the shortcut every site engineer learns. It is accurate to about 0.1%: the calculator uses the exact formula and shows both.


US bars use the nominal weights in ASTM A615 (lb/ft), so the result matches published charts.


Worked Example


20 bars of 16 mm, each 12 m long:


    

  1. Unit weight = 16² ÷ 162 = 256 ÷ 162 = 1.580 kg/m (exact: 1.578 kg/m)
    2. 

  2. Total length = 20 × 12 = 240 m
    3. 

  3. Weight = 1.578 × 240 = 378.8 kg (0.379 t)
    4. 



US example: 30 bars of #5, each 20 ft: 1.043 lb/ft × 600 ft = 625.8 lb.


Metric Rebar Weight Table






Bar size
kg per metre
kg per 12 m bar
Metres per tonne






6 mm
0.222
2.66
4,505




8 mm
0.395
4.74
2,534




10 mm
0.617
7.40
1,622




12 mm
0.888
10.65
1,126




14 mm
1.208
14.50
828




16 mm
1.578
18.94
634




20 mm
2.466
29.59
405




25 mm
3.853
46.24
260




32 mm
6.313
75.76
158






US Rebar Weight Table (ASTM A615)






Bar
Diameter
lb per ft
lb per 20 ft bar






#3
0.375 in
0.376
7.5




#4
0.500 in
0.668
13.4




#5
0.625 in
1.043
20.9




#6
0.750 in
1.502
30.0




#7
0.875 in
2.044
40.9




#8
1.000 in
2.670
53.4






Assumptions


    

  • Steel density 7,850 kg/m³; nominal (not measured) diameters.
    • 

  • Length is the cut length. Add laps, hooks and bends before entering it, or use the wastage field for a quick allowance.
    • 

  • To count bars in a slab or footing first, use the rebar quantity calculator.
    • 



Frequently Asked Questions
What is the formula for rebar weight?
Weight (kg/m) = D² ÷ 162, with D in mm. It comes from the bar's cross-section area × steel density (7,850 kg/m³). The exact divisor is 162.2, which is why tables show 0.888 kg/m for a 12 mm bar.
How much does a 12 m length of 16 mm rebar weigh?
16² ÷ 162 = 1.58 kg/m, so 12 m weighs about 18.9 kg.
How many metres of 12 mm bar are in one tonne?
About 1,126 m: 1,000 kg ÷ 0.888 kg/m. That is roughly 94 bars of 12 m.
How much does #4 rebar weigh per foot?
0.668 lb/ft. A 20 ft #4 bar weighs about 13.4 lb.
Why is my delivered tonnage different from the calculated weight?
Rolling tolerance allows actual bar mass to vary a few percent from nominal, and deliveries include offcuts, laps and bends. Calculated weight is the nominal figure used for estimating and payment.
References
  • ASTM A615/A615M: nominal dimensions and weights of US deformed bars
  • Steel density 7,850 kg/m³ (as used in BS 4449 and IS 1786 bar weight tables)
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