Let me show you the simple derivation of the most commonly used formula, D2/162.2, to determine the unit weight of the rod per meter length.

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**It follows as follows:**

**Density of steel**x Bar length

= (3.14 x D^2/4) x 7850 kg/㎥ x 1m

= (D^2 x 6162.25)/(1000 x 1000)

= D^2 x (0.006162)

= D^2 x 1/(0.006162)^-1

= D^2/162.28

**We use the following formula for easy calculation in problem solving or calculations:**

**Steel bar unit weight (in kg/s) = D2/162.**

**Where D is the steel bar's diameter in millimeters.**

**Remember:**

To calculate the **unit weight of steel**, the length “L’ becomes unity.

**Weight of Steel Bar = [ ****D^2**** L / 162.28] **in Kg and Length ‘L’ in m

**Weight of Steel Bar** = **[ ****D^2**** L / 533] **in Kg and Length ‘L’ in foot

Steel has a density of 7850kg/m3 in this case. The diameters of mild steel round bars are specified in millimeters (mm).

Unit Weight of Different Building Materials

## **For MS Flat Bar**

Weight of steel Flat bar = (Length x width x thickness) x 7850

**For example:**

MS Flat bar of width = 50mm

Thickness = 30mm.

As we know,

Weight of steel bar = Volume of steel Bar x Density of steel

Weight of steel bar = (Length x width x thickness) x 7850

Unit Weight of steel bar = (1 x .050 x .030) x 7850

= 11.775 kg/m

**Note: **

If you want to **calculate the weight of a circular steel bar**, use this formula (D2/4) and then multiply by the density of steel, which is 7850 kg/m3.

**For circular Steel Rods**

**The formula for the Unit weight of steel** = D^2/162 kg/m

**For example:**

If we want to calculate the unit weight of a 10-mm steel rod with a 1-meter length, we can use the formula

Weight of steel = 10^2/162

= 0.617 kg/m x 1m

= 0.617 kg

So, 1- meter of 10 mm steel weighs around **0.617 kg.**

The steel is usually brought in the big trolled on-site, and the rod length is about 12 meters.

So, if you want to calculate the length of a 12-meter rod, then

The steel unit weight for a 10 mm steel rod is 0.617 kg.

For 12 m=12 x0.617=7.40 kg

So, a 12 m long rod of 10mm dia weighs around **7.40 kg**

**Hence, the weight of** :

8mm dia bar = (8x8x1)/162 = 0.395 kg

10mm dia bar = (10x10x1)/162= 0.617 kg

12mm dia bar = (12x12x1)/162= 0.89 kg

16mm dia bar = (16x16x1)/162= 1.58 kg

20mm dia bar = (20x20x1)/162= 2.47 kg

25mm dia bar = (25x25x1)/162= 3.86 kg

32mm dia bar = (32x32x1)/162= 6.32 kg

**Steel bar weight can be calculated in two ways:**

## By the density of steel or by formula.

When calculating the weight of steel bars, always use the manufacturer's unit weight chart. Calculating weights in terms of the **cross-sectional** area does not produce accurate results. This is the simplest and most straightforward method for calculating steel weight without interpolation. Calculating each bar's unit weight yields the steel bar's total weight. It is computed following the final estimate of the total steel required for a construction project.

We provide main reinforcement bars in the short span of the slabs and **distribution bars** along the longer span of the slab.

Let's look at an example to help you understand. **EXAMPLE:**

Assume we have a one-way slab with a length of 5 m and a width of 2 m. (clear span). The main bars will be 12 mm long and spread 100 mm apart. The distribution bars will be 8 mm in diameter and spaced at 125 mm c/c. The clear cover will be 25 mm thick (top or bottom), and the slab will be 150 mm thick.

**Calculate the quantity of steel?**

**Calculate the weight of steel.**

**GIVEN DATA:**

Length = 5 m (5000 mm)

Width = 2 m (2000 mm)

Main Bar = 12 mm @ 100 mm c/c

Distribution Bar = 8 mm @ 125 mm c/c

Clear cover = 25 mm from (Top and Bottom) Thickness = 150 mm

**SOLUTION:**

The quantity is done into two steps.

Calculation of the number of bars

Cutting the length of bars

STEP 1: CALCULATION OF BAR NO'S

First, calculate the number of bars required (main and distribution).

FORMULA:

= (Total length — Clear cover)/center to centre spacing + 1

## Main bar:

= (5000 - [25+25])/100 + 1

= 4950 /100+1 = 51 Bars

Distribution bar:

= (2000 - + 1

= 1950/125+1

= 17 Bars

STEP 2. CUTTING LENGTHS:

MAIN BAR:

**FORMULA**

= (L) + (2 ×Ld)+ (1x 0.42D) - (2 x1d)

# Where

= Clear Span of the Slab

Ld = Development Length, which is 40 d (where d is the diameter of the bar)

0.42D = Inclined length (Bend length) 1d = 45° bends (d is diameter of bar)

## First, calculate the length of "D."

= (Thickness) - 2 (Clear cover at Top, BOTTOM)

— Diameter of the bar

= 150 - 2(25) -12

= 88 mm

By putting Values

**Cutting length:**

= 2000+(2x40x12) + (1 x0.42 x 88)

- (2x1 x 12)

= 2000 + 960 + 36.96 - 24

= 2972.96 mm 2973 mm or 2.973 m

DISTRIBUTION BAR:

= Clear Span + (2 x Development Length (Ld))

= 5000 + (2 x 40 x 8)

= 5640 mm or 5.64 m Ans

**CONCLUSION:**

**1: Main bar:**= 51 No's Length:

= 51 x 2.973 m = 151.623 m Weight:

= (D2/162) x length

= 134.776 kg

**2: Distribution Bar:**= 17 No's Length:

= 17 x 5.64m = 95.88 m Weight:

= (D2/162) x length

= 37.87 kg