Calculation formula of section area of round steel bar and its weight scale
Formula for calculating the section area of round steel bar
To find the sectional area of a plane circle from its radius, S=π r^{2} is 3.14×r×r = area^{ 2}
π is PI =3.14, and r is the radius of the circle
Examples:
The diameter of a steel bar is 35MM, seek its area?
A: 3.14 * 17.5 * 17.5
Area = 961.6252mm
Rebar specification theory weight scale
Table of Contents
Dimensions, external weight and allowable deviation of hotrolled bar (Round bar); Theoretical weight scale of specifications (GB/T1498194)
The diameter of mm 
Allowable deviation, mm 
Roundness, mm 
Crosssectional area mm^{2} 
Theoretical weight Kg/m 

A level precision 
Class B precision 
C level precision 
A level precision 
Class B precision 
C level precision 

5.5 
+ / – 0.40

+ / – 0.30  + / – 0.15 
0.50 or less
Online calculator

0.40 or less

0.24 or less

23.8

0.187 
6.0 
28.3

0.222  
6.5 
33.2

0.260  
7.0 
38.5

0.302  
7.5 
44.2

0.347  
8.0 
50.3

0.395  
8.5 
56.7

0.445  
9.0 
63.6

0.499  
9.5 
70.9

0.556  
10.0 
78.5

0.617  
10.5 
+ / – 0.45

+ / – 0.35

+ / – 0.20

0.60 or less 
0.48 or less

0.32 or less  86.6  0.680 
11.0 
95.0

0.746  
11.5 
104

0.815  
12.0 
113

0.888  
12.5 
123

0.963  
13.0 
133

1.04  
13.5 
143

1.12  
14.0 
154

1.21  
14.5 
165

1.30  
15.0 
+ / – 0.50

+ / – 0.40

+ / – 0.25

0.70 or less

0.56 or less

+ / – 0.40  177  1.39 
15.5  189  1.48  
16.0 
201

1.58 
Calculation formula: Radius x radius x 3.14 x per meter x 0.785
For example: the diameter of 6.0 steel bar, (0.03×0.03×3.14)×100×0.785=0.221841
In parentheses is the crosssectional area, 3.14 is PI, 100 is centimeters (per meter), and 0.785 is specific gravity per square centimeter, so all values are converted to uniform units for calculation
Round steel theoretical weight scale
General specific gravity of steel:
 Chromium steel 15CrA 20Cr, 7.74
 Ordinary carbon steel Q195, Q215, Q235, Q255, Q275 7.85
 05F, 08F, 15F 10, 15, 20, 25, 30, 35, 40, 45, 50 7.85
 Carbon tool steels T7, T8, T9, T10, T12, T13, T7A, T8A, T9A, T10A, T11A, T12A, T13A, T8MnA 7.85
 Silicon manganese steel 60Si2nMnA 7.85
Specifications of the diameter  The weight per meterkg/m  The diameter of  The weight per meterkg/m 
5.5  0.186  13  1.04 
6  0.222  14  1.21 
6.5  0.26  15  1.39 
7  0.302  16  1.58 
8  0.395  17  1.78 
9  0.499  18  2.0 
10  0.617  19  2.23 
11  0.746  20  2.47 
12  0.888  21  2.72 
22  2.98  63  24.5 
23  3.26  65  26 
24  3.55  68  28.5 
25  3.85  70  30.2 
26  4.17  75  34.7 
27  4.49  80  39.5 
28  4.83  85  44.5 
29  5.18  90  49.9 
30  5.55  95  55.6 
31  5.92  100  61.7 
32  6.31  105  68 
33  6.71  110  74.6 
34  7.13  115  81.5 
35  7.55  120  88.8 
36  7.99  125  96.3 
38  8.9  130  104 
40  9.86  140  121 
42  10.9  150  139 
45  12.5  160  158 
48  14.2  170  178 
50  15.4  180  200 
53  17.3  190  223 
55  18.6  200  247 
56  19.3  220  298 
58  20.7  250  385 
60  22.2  
Formula: Radius x radius x 3.14 x per meter x 0.785
For example: the diameter of 6.0 steel bar, (0.03×0.03×3.14)×100×0.785=0.221841 In parentheses is the crosssectional area, 3.14 is PI, 100 is centimeters (per meter), 0.785 is the specific gravity per square centimeter, so all values are converted into uniform units for calculation 
Rebar theoretical weight scale
Thermal Gadolinium reinforcement (rebar) specification theory weight scale for reinforced concrete complete/per meter 

Type d0
(millimeter) 
Inside diameter d
(millimeter) 
Outside diameter d1
(millimeter) 
Theoretical weight
(kg/m) 
6  5.75  6.75  0.222 
7  6.75  7.75  0.302 
8  7.5  9.0  0.395 
9  8.5  10.0  0.499 
10  9.3  11.3  0.617 
12  11  13.0  0.888 
14  13  15.5  1.21 
16  15  17.5  1.58 
18  17  20.0  2.00 
20  19  22.0  2.47 
22  21  24.0  2.98 
25  24  27.0  3.85 
28  26.5  30.5  4.83 
32  30.5  34.5  6.31 
36  34.5  39.5  7.99 
40  38.5  43.5  9.87 
Source: Network Arrangement – China Steel Bar Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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