In civil engineering, lots of thumb rules are using to find the quick result as we need and those thumb rules give us an approx value not an accurate.

We can’t calculate each and everything at field sometimes we have to act quickly to move on. Every professional have been maintaining some thumb rules to make the result quickly.

At first, we have to understand the meaning of thumb rule before jump into the discussion. Thumb rules mean “ **Approximate**”.

Thumb rules play a vital role in the construction and don’t forget one thing when we use thumb rule no units system has to be followed so ignore the units. (Read below content to understand what I mean it!.)

Mostly we may use the thumb rules like concrete calculation, manpower estimation, the material requirement for plastering, wastage’s calculation, brickwork calculation, etc.,

For example,

What is the requirement of bricks for 1 Cum? As per the calculation 625 nos.

But we Say Approx 600 nos. It is called as a thumb rule. Because we can not estimate every time.

# Thumb rule in construction

We are using many thumb rules in construction and it is indirectly used to find the approximate cost and time to execute the work.

As above said, Thumb rules are not given accurate result it just gives us an approx result. Let’s discuss the thumb rules which is used in various works of construction.

## Thumb rule for Manpower Productivity Estimation

In fact, the manpower productivity has obtained from practical work done of the labours which we used to calculate the output for particular work.

SI | Manpower | Activity | Out Put - 8 Hours |
---|---|---|---|

1 | Mason - 1 Male mazdoor - 0.75 Female Mazdoor - 0.5 | Brick Work | 45 Cft |

2 | Mason - 1 Male mazdoor - 1 Female Mazdoor - 0.5 | Wall plastering | 120 Sft |

3 | Mason - 1 Male mazdoor - 0.75 Female Mazdoor - 0.5 | Ceiling Plastering | 90 Sft |

4 | Carpenter-2.25 Foreman- 0.2 Helper- 2.25 | Shuttering Work | 11 Sqm |

5 | Bar Bender - 1 Nos Helper - 1 Nos | Steel Work | 100 Kg |

6 | Tile Mason - 1 Nos Helper - 1 Nos | Tile Work | 10 Sqm |

7 | Mason - 2 Male mazdoor - 1.75 Female Mazdoor - 1.75 | Block Work | 2 Cum |

8 | Male Coolie - 5 Nos Female Coolie - 4 Nos | Earth Digging | 1000 Cft |

## Thumb rule for concrete work

The quantity ingredient material for concrete will be vary based on the mix ratio and the concrete volume 0.04 cum per sft for the plinth area.

#### Example

If the Plinth area will be 100 Sft (10 x 10) So now the approximate required concrete volume for the building is 100 x 0.04 = 4 Cum.

The concrete has prepared with mixing of Cement, Sand, Coarse aggregate and water. The cement and water are called binding material.

### Thumb Rule of Concrete material requirement

Grade | Ratio | Cement in Bags | Sand in Cum | Coarse Aggregates in Cum |
---|---|---|---|---|

M5 | 1:5:10 | 2.77 | 0.48 | 0.96 |

M7.5 | 1:4:8 | 3.41 | .047 | 0.95 |

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 |

M25 | 1:1:2 | 11.09 | 0.39 | 0.77 |

**Must Read:- What is water cement Ratio**

## Thumb rule for Plastering Work

The material quantity will vary based on the different mix ratio like concrete and the thumb rule for plastering work has listed below.

Type of Plastering | Mix ratio | Thickness in MM | Cement Bags/Sqm | Sand Cum/Sqm |
---|---|---|---|---|

Inner Plastering | 1:3 | 15 | 0.16 | 0.017 |

External Plastering | 1:4 | 20 | 0.17 | 0.024 |

Rough Plastering | 1:5 | 16 | 0.11 | 0.020 |

Ceiling Plastering | 1:2 | 12 | 0.17 | 0.012 |

**To know more How to calculate material for Plastering work**

## Thumb rule for Brick Work

The size of brick 190mm x 90mm x 90mm

Number of bricks per cum = 500 Nos

**Must read: How to calculate the number of bricks **

Mix Ratio and brickwork thickness | Mortar Thickness in MM | Cement in Bags | Sand in Cum |
---|---|---|---|

1:6 200mm Thk | 10 | 1.4 / Cum | 0.30 |

1:5 200mm Thk | 10 | 1.7 / Cum | 0.25 |

1:4 100mm Thk | 10 | 0.15 / Sqm | 0.035 |

1:5 200mm Thk Block | 10 | 0.15 / Cum | 0.020 |

## Thumb rule for Steel in RCC

The steel cost very expensive compared to other construction material and the exceed of steel requirement impact the project budget. A good designer restrains steel utilization.

Type of Structure | Steel Kg/Sft |
---|---|

Residential Building | 2.5 to 4.5 |

Commercial Building | 4.5 to 5.5 |

Mass Project Tall or heavy Structure | 6 to 8 |

The steel percentage against concrete volume will vary based on the structural element and the minimum and maximum percentage of steel utilization have listed below as per IS standard.

Thumb rule for steel in RCC has listed below.

Structural Element | Percentage of Steel in Concrete |
---|---|

Slab | 1% |

Beam | 1% to 2% |

Column | 2.5% |

**Must Read: How to calculate steel weight for Reinforcement**

#### Example calculation:

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

For example, if a volume of concrete 1 cum.

Approx Steel requirement = 1 x 1% x 7850 = 78.5 Kg/Cum.

**Read: Bar bending Shape codes**

## Thumb rule for shuttering work

The shuttering work is called by another is “Form Work” because it gives a uniform shape and smoothness for the concrete. Generally, it takes 10% to 15% of the cost of the total budget.

Thumb rule for shuttering work is listed below.

Type of Concrete Element | No of Times Sqm Per Cum |
---|---|

Foundation | 2 to 3 of concrete volume |

Column | 11 to 13 of concrete volume |

Beam | 11 to 12 of concrete volume |

Slab | 6 to 8 of concrete volume |

For example, if the slab concrete volume 1 cum then the approx shuttering requirement is 1 x 6 = 6 Sqm.

Hope you well know about so many thumb rule in Civil Engineering!.