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
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
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.
||Percentage of Steel
||1% of total volume of concrete
||2% of of total volume of concrete
||2.5% of total volume of concrete
||0.8% of total volume of concrete
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
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
For every 15m2 of shuttering 1 litre of shuttering oil is consumed.
15m2 is total area of shuttering, then Shuttering oil required = 0.065 x 15 = 0.975 lts
Thumb rule for Cement, Sand, Coarse Aggregate Quantity in Different grades of Concrete :
||Coarse Aggregate Quantity
||Fine Aggregate Quantity
Note: 1 bag of cement = 50Kgs
Thumb rule for Cement quantity in Brickwork, Cement Masonry & Plastering work in construction:
Brickwork Thumb rule:
|Brickwork for 1m3
|230 mm Brickwork
|115 mm Brickwork
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
|150mm in Cement Masonry work of ratio 1:6
|200mm in Cement Masonry work of ratio 1:4
|150mm in Cement Masonry work of ratio 1:4
|100mm in Cement Masonry work of ratio 1:4
Plastering Quantity Thumb Rule:
|Type of Plastering
||Cement Qty in Bags
||Cement Qty in Kgs
|Internal Wall Plastering
|External Wall plastering