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Thumb rules Used In Construction
A Thumb rule is an approximate & comparing method to calculate the quantity of different materials required for construction.
Thumb rules play an essential role for site engineers/site supervisors while making quick decisions on site.
Thumb rules help you calculate the quantity using a simple mathematical formula and make intelligent decisions whenever required.
In thumb rules, The measuring units are different when comparing to get the solution. Hence never consider units while using the thumb rule.
Remember, thumb rules never provide exact quantity, but you can use them for approximate quantity.
We apply many thumb rules in construction, and here I am sharing some Thumb rules that are most frequently used on site.
Thumb Rule for Volume of Concrete for the plan area.
The concrete volume required for per square feet plans area = 0.038 m3/square feet plan area.
Example – If the Plan Area = 25 x 40 = 1000 Sq. m. then total volume of concrete needed = 1000 x 0.038m3 = 38 m3.
Thumb Rule For Steel In Building Construction
Following are some essential thumb rules for calculating steel quantity for different buildings.
Steel needed for residential buildings = 4.5 Kgs – 4.75 Kg / sq. Ft.
Steel needed For Commercial buildings = 5.0 Kgs – 5.50 Kg/Sq. Ft.
You can also follow BN Datta’s recommendations for the more exact quantity.
Percentage of Steel For Different Structural Members
Following are some essential thumb rules for calculating steel quantity for Footings, Columns, Beam & Slab
1) Slab – 0.8 to 1% of total concrete volume (Slab steel calculation thumb rule)
2) Beam – 1 to 2% of total concrete volume
3) Column – 2 to 5 % of total concrete volume
4) Footings – 0.6 to 0.8% of total concrete volume
Example
How to calculate the quantity of steel for a slab having dimensions 6m x 5m x 0.15m?
Step 1: Calculation of the Concrete Volume.
Total Concrete volume for Slab above mentioned slab = 6 x 5 x 0.15 = 4.5m3
Step 2: Calculation of Steel Quantity Using above mentioned percentage
As per the BN Dutta reference book, the quantity of steel for the slab is 1% of the total concrete volume.
Thumb rule to estimate the quantity of steel for slab mentioned above = Concrete Volume x Steel density x % of Steel for Member
Steel required for the slab = 4.5 x 7850 x 0.01 = 353.25Kgs
For exact estimation, you can learn from Bar Bending Schedule.
Thumb Rule for shuttering Area Calculation
Shuttering helps to shape the concrete, and its cost is 15 to 18% of the total construction cost.
The Thumb rule to determine the area of shuttering needed is 2.4 times the plinth area or six times the concrete quantity.
Consider, the quantity of concrete is one cubic meter, then the shuttering area needed is 1 x 6 = 6 square meters.
Members of Shuttering
Ply, Battens, Nails are members of Shuttering.
Calculation For Shuttering Ply
The shuttering Ply has dimensions 2.44 x 1.22 x 0.012 length, width, and thickness.
The Numbers of Shuttering Ply sheets needed = 0.22 times of Shuttering Area
Assume the area of shuttering is = 5m
Then the Ply required for shuttering = 0.22 x 5 = 1.1 numbers
The calculation for battens Quantity
Batten usually have a width and thickness of 75mm x 40mm.
Batten Quantity = 19.82 x Numbers of Ply Sheets
If we need 25 Plyboard for construction, the total quantity of Battens is 19.82 x 25 = 495 Battens.
Nails & Binding Wire Quantity Calculation For shuttering
For one square meter of shuttering, nails required are 75 grams.
For every one square meter of shuttering, the binding wire needed is 75 grams.
Thumb rule for oil Quantity required for shuttering:
Oil is applied on the surface of ply or metal plates for easy removal of shuttering.
Quantity of oil needed for shuttering is = 0.065 x Total Shuttering Area
(or)
For a 15 square meters area of shuttering, 1 litre of oil is needed.
Example
If the total area of shuttering is 15 square meter, then oil required is = 0.065 x 15 = 0.975 liters.
Thumb Rule To Calculate the Quantity of Materials Needed For Different Grades of Concrete.
For one cubic meter
| Concrete Grade | Cement in Bags | Sand in Cum | Aggregate in Cum |
|---|---|---|---|
| M5 (1:5:10) | 2.77 | 0.48 | 0.96 |
| M7.5 (1:4:8) | 3.41 | 0.47 | 0.94 |
| M10 (1:3:6) | 4.44 | 0.46 | 0.92 |
| M15 (1:2:4) | 6.34 | 0.44 | 0.88 |
| M20 (1:1.5:3) | 8.06 | 0.42 | 0.84 |
Thumb Rule to Calculate Material Required for Brickwork
| Brickwork | Cement Quantity in bags | Cement Quantity in Kg |
|---|---|---|
| 230 mm Brickwork | 0.876bags/m3 | 43.80 |
| 115 mm Brickwork | 0.218bags/m3 | 10.90 |
Thumb Rule to Calculate Cement for Masonry
| Cement Masonry Type & Mix | Cement Quantity in bags | Cement Quantity in Kg |
|---|---|---|
| 200mm Masonry work of ratio 1:6 | 0.124Bags/m2 | 6.2Kg/m2 |
| 150mm Masonry work of ratio 1:6 | 0.093Bags/m2 | 4.65Kg/m2 |
| 200mm Masonry work of ratio 1:4 | 0.206Bags/m2 | 10.3Kg/m2 |
| 150mm Masonry work of ratio 1:4 | 0.144Bags/m2 | 7.2Kg/m2 |
| 100mm Masonry work of ratio 1:4 | 0.103Bags/m2 | 5.15Kg/m2 |
Thumb Rule For Plastering Material Quantity
| Plaster Type | Cement Quantity in bags | Cement Quantity in Kg |
|---|---|---|
| Rough Plaster | 0.09Bags/m2 | 4.5Kg/m2 |
| Internal Wall Plaster | 0.09Bags/m2 | 4.5Kg/m2 |
| Duct Plastering | 0.09Bags/m2 | 4.5Kg/m2 |
| External Wall Plaster | 0.175Bags/m2 | 8.75Kg/m2 |
| Stucco Plaster | 0.175Bags/m2 | 8.75Kg/m2 |
| Lathen Plastering | 0.55Bags/m2 | 27.5Kg/m2 |
Thumb Rule To Determine Labour Productivity
| Type of Work | Type of Labour | Productivity 8 Hours |
|---|---|---|
| Brickwork | 1 Mason 1Male Mazdoor 1Female Mazdoor | 1.27 Cum |
| Wall Plaster | 1 Mason 1Male Mazdoor 1Female Mazdoor | 12 Sqm |
| Ceiling Plaster | 1 Mason 1Male Mazdoor 1Female Mazdoor | 8 Sqm |
| Block Work 4″ | 1 Mason 1Male Mazdoor 1Female Mazdoor | 8 Sqm |
| Block Work 6″ | 1 Mason 1Men Mazdoor 1Woman Mazdoor | 8 Sqm |
| Block Work 8″ | 1 Mason 1Male Mazdoor 1Female Mazdoor | 10 Sqm |
| Bar Bender | 1 Skilled 1 Unskilled | 200 Kg |
| Carpenter | 1 Skilled 1 Unskilled | 4 Sqm |
| Tile Work | 1 Mason 1Male Mazdoor | 10 Sqm |
Also, Read
House Construction Cost Calculator Excel Sheet
Estimate of Building Work – Long Wall Short Wall Method, Centre Line Method