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Important Thumb Rules for Estimation in Civil Engineering

We can’t calculate each and everything in the field.

Sometimes we have to act quickly to move on. Every professional have maintained their own set of thumb rules. 

What is Thumb Rule?

At first, we have to understand the meaning of thumb rule before jumping into the discussion.

• Thumb rules are “ Approximate Value”.  
• Thumb Rules has no unit systems

We use the thumb rules for almost in every calculation 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 according to the individual requirement.

Thumb rule for Manpower Productivity Estimation

Manpower productivity thumb rules will be useful to calculate the total manpower required for your next schedule.

SI	MANPOWER	ACTIVITY	OUTPUT - 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 Soft
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 concrete ingredients will be vary based on the mix ratio.

For Example, 

If the Plinth area is 100 Sq.ft (10 x 10) and the required concrete volume is 100 x 0.04 = 4 Cum with M5 mix ratio means

Now from the below table which is for 1 m3

Required Concrete ingredients for 4 m3 of M5 is

Cement – 2.77 x 4 = 11.08 bags

Sand – 0.48 x 4 = 1.92 cum

Coarse aggregate = 0.96 x 4 =  3.84 cum

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

For plastering, the material quantity will vary based on the different mix ratios 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 excess purchase 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.

The 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:

Steel quantity = Volume of Concrete x Density of Steel x % of Steel.

For example, if a volume of concrete 1 cum for a slab.

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

Read: Bar bending Shape codes

Thumb rule for shuttering work

The shuttering work is called by another name “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.

The Thumb rule for shuttering work is listed below.

TYPE OF CONCRETE ELEMENT	NO OF TIMES SQM PER CUM
Foundation	2 to 3 times of concrete volume
Column	11 to 13 times of concrete volume
Beam	11 to 12 times of concrete volume
Slab	6 to 8 times of concrete volume

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

If we have missed anything please do let us know to update! 

Do you have any kind of thumb rules for yourself? If so share it with us in the comment section we would like to also learn something from you.

thanks to 

CIVIL PLANETS

Er.SP.ASWINPALANIAPPAN., M.E.,(Strut/.,)

Structural Engineer

Madras Terrace Architectural Works

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