Important Thumb Rules used in Construction by Civil Engineers

Thumb rules play a most crucial role while taking quick decisions on site. Thumb rules enable you to calculate the solution using a simple mathematical formula and make smart decisions whenever needed. Remember, thumb rules never give the accurate results, but you can use them for approximate results. There are many thumb rules which we apply in construction. Here I am discussing the most frequently used Thumb rules on site.

Thumb rule is an approximate & comparing method. In thumb rules, The units are not the same when we compare to get the results. So never consider units while performing thumb rule.

Thumb rule to calculate the Concrete Volume with respect to area:

The Concrete Volume of 0.038m3 of concrete is used for each Square Feet of Plan area

Example:-

From below fig: Plan Area = 40 x 20 = 80SFT

The plan area is 80SFT then the total volume of concrete required = 800 x 0.038m3 =30.4m3

You can learn more about Concrete Volume calculation 

Thumb rule to calculate the Steel quantity required for Slab, Beams, Footings & Columns:

For Residential buildings 4.5Kgs-4.75Kgs /SFT

For Commercial buildings 5.0Kgs-5.50Kgs/SFT

For more accurate results you can also use BN Datta recommendations:

As per B N Datta, the Steel quantity used in different members of the building can be calculated easily using the following recommendations.

Structural Member	Percentage of Steel
Slab	1% of total volume of concrete
Beam	2% of of total volume of concrete
Column	2.5% of total volume of concrete
Footings	0.8% of total volume of concrete

Example:

How to calculate the steel quantity of slab having the Length, width, and depth of the slab is 5m x 4m x 0.15m

Step 1: Calculate the Volume of Concrete

Total Volume of Concrete for above given Slab is 5 x 4 x 0.15 = 3m3

Step 2: Calculate the steel quantity using formula

As per the above table, the steel quantity of slab is 1% of the total volume of concrete utilized.

Thumb rule to calculate Steel quantity of above slab = Volume of Concrete  x Density of Steel x % of Steel of Member

Steel quantity required for above slab = 3 x 7850 x 0.01 = 235Kgs

For accurate calculation, you can refer to Bar Bending Schedule

Thumb rule to calculate the Shuttering area:

Shuttering costs 15-18% of the total construction of the building. Shuttering is framed to bring the concrete in Shape. Thumb rule to calculate the shuttering required is 6 times the quantity of concrete or 2.4 times of Plinth area.

Suppose, the concrete quantity is 0.5m3 then the shuttering area required is  0.5 x 6 = 3m2

Components of Shuttering:-

Shuttering Ply, Battens, Nails are components of Shuttering.

Shuttering Ply Quantity calculation:

The shuttering Ply has a length, width & depth of 2.44 x 1.22 x 0.012

The No. of Shuttering Ply sheets = 0.22 times of Shuttering

Suppose, the area of shuttering required = 3m

Then the Shuttering Ply required = 0.22 x 3 = 0.66m2

Battens Quantity Calculation:

Shuttering batten usually have a length & width of 75mm x 40mm.

Batten Quantity = 19.82 x No. of Ply Sheets

if the construction requires 25 Ply sheets, the total quantity of Battens are 19.82 x 25 = 495 Battens

Nails & Binding Wire Quantity in Shuttering:

75gms of Nails are used for 1m2 of Shuttering

75gms of Binding wire is consumed for every 1m2 of Shuttering.

Thumb rule for Shuttering oil Quantity:

Shuttering oil is used to de-frame or de-assemble from the concrete easily.

Total required Shuttering oil is = 0.065 x Total Area of Shuttering

(or)

For every 15m2 of shuttering 1 litre of shuttering oil is consumed.

Example :

15m2 is total area of shuttering,  then Shuttering oil required = 0.065 x 15 = 0.975 lts

For Accurate Shuttering Area Calculation, You can check here Shuttering area required for slabs, columns, Beams, Footings

Thumb rule for Cement, Sand, Coarse Aggregate Quantity in Different grades of Concrete :

Concrete Mix	Cement Quantity	Coarse Aggregate Quantity	Fine Aggregate Quantity
M5 (1:5:10)	2.82 Bags	0.98m3	0.49m3
M7.5(1:4:8)	3.48 Bags	0.97m3	0.48m3
M10(1:3:6)	4.50 Bags	0.90m3	0.45m3
M15(1:2:4)	6.60 Bags	0.88m3	0.44m3
M20(1:1.5:3)	8.40 Bags	0.84m3	0.42m3

Note: 1 bag of cement = 50Kgs

For Accurate calculation refer to Concrete Mix design for Different grades of concrete

Thumb rule for Cement quantity in Brickwork, Cement Masonry & Plastering work in construction:

Brickwork Thumb rule:

Brickwork for 1m3	Cement Qty in m3	Cement Qty in Bags
230 mm Brickwork	0.876m3	25.4 Bags
115 mm Brickwork	0.218m3	6.32 Bags

Cement Masonry Quantity Thumb Rule:

Cement Masonry Type & Mix	Cement Qty in Bags	Cement Qty in Kgs
200mm in Cement Masonry work of ratio 1:6	0.124Bags/m2	6.2Kgs/m2
150mm in Cement Masonry work of ratio 1:6	0.093Bags/m2	4.65Kgs/m2
200mm in Cement Masonry work of ratio 1:4	0.206Bags/m2	10.3Kgs/m2
150mm in Cement Masonry work of ratio 1:4	0.144Bags/m2	7.2Kgs/m2
100mm in Cement Masonry work of ratio 1:4	0.103Bags/m2	5.15Kgs/m2

Plastering Quantity Thumb Rule:

Type of Plastering	Cement Qty in Bags	Cement Qty in Kgs
Rough Plastering	0.09Bags/m2	4.5Kgs/m2
Internal Wall Plastering	0.09Bags/m2	4.5Kgs/m2
Duct Plastering	0.09Bags/m2	4.5Kgs/m2
External Wall plastering	0.175Bags/m2	8.75Kgs/m2
Stucco Plastering	0.175Bags/m2	8.75Kgs/m2
Lathen Plastering	0.55Bags/m2	27.5Kgs/m2