Methods of Taking Out Quantities in Construction

 Introduction

One of the most important pre-execution activities in any construction project is measurement and quantity estimation of various inputs like materials, labor, and equipment. This process is generally known as taking out quantities or quantity takeoff. It is the basis of cost estimation, tendering, budgeting, and procurement of materials.

Quantity measurements ensure that projects meet their budget criterion, are timely, and minimize waste. Understanding the methods of taking out quantities is important for the financial and technical success of construction projects by civil engineers, contractors, and quantity surveyors.

The definition, importance, methods, and procedures concerning quantity take out for different types of construction works are discussed in this article.

What is Quantity Takeoff in Construction?

Quantity takeoff, also called "Taking out Quantities", is the process of measuring and listing all materials and work items required for a construction project.

It involves determining the length, area, volume, and number of items directly from drawings and design specifications.

For example:

• Quantities of bricks needed for walls.

• The volume of concrete for foundations or slabs.

• Quantity of steel reinforcement in beams or columns.

All these quantities are listed in a systematic manner in a Bill of Quantities, or Measurement Sheet.

Purpose of Taking Out Quantities:

1. To prepare cost estimates before construction.
2. To plan procurement of materials and resources.
3. To invite tenders and bids based on accurate data.
4. To prepare project budgets and financial forecasts.
5. To control wastage and ensure efficient material usage.
6. To compare actual vs. estimated quantities during project execution

Importance of Quantity Take off in Construction:

1. Budget Accuracy
It provides the general quantities required for an accurate cost estimation of materials, labor, and equipment.

2. Resource Management
It ensures the correct amount of material is bought and delivered at the right time, avoiding delays.

3. Tender Preparation
These quantities are used by contractors when preparing competitive tenders to avoid under- and overbidding.

4. Cost Control
By comparing actual consumption with estimated quantities, waste can be promptly spotted and cost performance tracked by engineers.

5. Project Scheduling
Quantitative data assists in the planning of the sequence of construction and the estimation of project duration.

Units of Measurement:

Before discussing methods, it’s important to understand units of measurement, since quantities are expressed differently for various construction items:

Work Item	Unit of Measurement
Earthwork	Cubic meter (m³)
Brickwork	Cubic meter (m³)
Concrete	Cubic meter (m³)
Plastering	Square meter (m²)
Flooring	Square meter (m²)
Steel reinforcement	Kilogram (kg) or tone
Painting	Square meter (m²)
Doors and windows	Number (No.) or Square meter (m²)

Accurate measurement using these standard units ensures uniformity and reliability.

Methods of Taking Out Quantities:

There are several methods used by civil engineers and quantity surveyors in calculating quantities, depending on the nature of the structure, complexity, or drawings available. The major methods of taking out quantities in construction are: 

1. Centre Line Method 

2. Crossing Method 

3. Out-to-Out and In-to-In Method 

4. Bay Method 

5. Partly Centre Line and Partly Cross Method 

6. Separate Wall Method 

Now, let's understand each one in detail.

1. Centre Line Method

Definition
In this method, the total centre line length of all the walls (internal and external) is calculated and quantities are worked out by multiplying this length with the respective breadth and depth.

Procedure
1. From the plan, determine the centre line length of walls.

2. Multiply it by the breadth and depth for each item, such as excavation, foundation, and brickwork.

3. Make corrections for openings, junctions, and offsets.

Example
If a wall has a centre line length of 40 m, width 0.3 m and height 3 m:
Volume=40×0.3×3=36m3Volume = 40 × 0.3 × 3 = 36 m³Volume=40×0.3×3=36m3

Advantages
• Fast and simple for symmetrical buildings.

• Reduces repetitive measurement work.

• Ideal for long, continuous walls.

Disadvantages

• Not suitable for buildings that have irregular shapes or unsymmetrical layouts.

• Junction corrections need special care in order to avoid errors.

2. Crossing Method

Definition
Internal dimensions are measured and all intersecting (crossing) points are adjusted in the crossing method. This is useful for calculating junctions and overlaps in construction elements like walls and beams

Procedure
1. Measure the length and width for each wall segment.

2. Calculate the volume of every part such as excavation, foundation, wall.

3. Add all components together to obtain the overall amount.

Advantages

• Appropriate for unsymmetrical buildings or buildings with different wall thicknesses.

• Provides accurate results for complex layouts.

Disadvantages

• More time-consuming; requires more detail in calculation.

• Prone to manual error, if not recorded carefully.

3. Out-to-Out and In-to-In Method

Definition

In this method, the walls are taken separately for the external (Out-to-Out) and internal (In-to-In) dimensions to find out the quantity.

Procedure

• Measure out-to-out for outer dimensions of exterior walls

• Measure inner dimensions (In-to-In) for internal walls.

• Quantities are worked out for different sections like foundation, plinth, and superstructure.

Advantages

• Useful for thick-walled structures.

• Appropriate for complex shapes and multi-room buildings.

Disadvantages

• Time-consuming since each wall has to be measured separately.

• Chance of 'cascading failures' at interchanges.

4. Bay Method

Definition

The bay method applies to those buildings that are divided into bays, meaning the spaces between regularly spaced columns, beams, or rooms. The quantities for one bay are calculated and then multiplied by the total number of bays.

Procedure

1. Measure one typical bay completely.

2. Calculate the quantity for one bay.

3. Multiply by the total number of similar bays.

Example

If one bay has 15 m³ of concrete and there are 10 identical bays:

TotalConcrete=15×10=150m3Total Concrete = 15 × 10 = 150 m³TotalConcrete=15×10=150m3

Advantages

• Saves time for repetitive structures like factories, hostels, and schools.

• Ensures uniformity and accuracy.

Disadvantages

• Not applicable for bays that differ in size or shape.

• Requires uniform design for accuracy.

5. Partly Centre Line and Partly Cross Method

Definition

This mixed method is used when a building has both symmetrical and unsymmetrical portions.

• The centre line method is used for symmetrical parts.

• Crossings apply to sections that are irregular.

Advantages

• Provides flexibility and higher accuracy.

• Ideal for complex buildings, such as hospitals or large offices.

Disadvantages

• It requires experience and careful coordination between both methods.

6. Separate Wall Method

Definition

In this process, each wall is measured separately along its full length, breadth, and height. Individual quantities are worked out and added together.

Procedure

1. Measure each wall separately.

2. Subtract openings like doors and windows.

3. Add all wall quantities to get the total.

Advantages

• Highly accurate for irregular layouts and buildings with variable thicknesses of walls.

• Easy to verify and audit later.

Disadvantages

• Time-consuming and labor-intensive.

• Not suitable for large-scale projects.

Precautions During Quantity Takeoff

1. Use latest approved drawings only.
2. Follow the standard measurement rules (IS 1200).
3. Deduct openings like doors, windows, and niches accurately.
4. Avoid double counting of junctions.
5. Maintain neat and organized measurement sheets.
6. Verify all dimensions before calculation.
7. Round off figures properly to avoid confusion.

Role of Software in Quantity Takeoff

Modern construction practices use digital tools to improve accuracy and speed. Some popular quantity takeoff software includes:

• AutoCAD + Excel: Manual quantity extraction and calculation.
• PlanSwift: For electronic measurement directly from PDF drawings.
• Revit (BIM): 3D model-based estimation.
• Bluebeam Revu: Digital markups and takeoffs.
• CostX: Integrated cost estimating and takeoff solution.

These tools help minimize human errors, increase transparency, and generate automatic Bills of Quantities (BOQ).

Applications of Quantity Takeoff

1. Estimation and Costing: Determines cost of a project before construction begins.
2. Tendering and Contracting: Used for preparing and analyzing tenders.
3. Procurement Planning: Helps in planning and scheduling the purchase of materials.
4. Project Monitoring: Involves comparing the actual quantities used to the planned quantities.
5. Billing and Payments: Ensures that work done is paid for accurately.
6. Quality Control: Assists in verifying that the work done conforms to the design.

Conclusion

The process of taking out quantities in construction is vital for the success of any building project. It forms the base for cost estimation, tendering, budgeting, and resource planning.

The Centre Line Method, Crossing Method, Bay Method, and Separate Wall Method are employed in different ways according to the type of structure and layout.

Precise measurement and calculation are the basis for financial stability, material efficiency, and timely completion of a project. Modern software, along with standard codes, has made quantity takeoff more accurate, transparent, and speedier.

In other words, learning the methods for taking out quantities is important for every civil engineer, quantity surveyor, and construction professional who wants to meet the goals of quality, economy, and sustainability in construction.