---
title: "Short note: Centre line method"
subject: "Estimating and Costing"
chapter: 2
key: "semester_7/estimating_and_costing:short-note-centre-line-method"
source: https://www.bctengineer.com/q/semester_7/estimating_and_costing/short-note-centre-line-method
site: BCT Engineering
---

# Short note: Centre line method

Estimating and Costing · Chapter 2: Method of Estimating

- Asked in: 2066 Bhadra (old course), 2 marks
- Video: [Estimation of One Room || Centre Line Method || @CivilConceptandPlans](https://www.youtube.com/watch?v=A_EKIinAZeI) — Civil Concept and Plans
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/estimating_and_costing/short-note-centre-line-method
- Whole chapter: https://www.bctengineer.com/md/semester_7/estimating_and_costing/chapter-2

## Question

Write a short note on the centre line method.

## Short answer

Centre line method uses total centre-line length corrected by deducting half the wall width for each T-junction (cross-junction counts as two). Multiply corrected length by width and depth. For a 4 x 3 m room with 0.23 m wall, trench volume is 13.43 m3.

## Answer

The centre line method is a quick way of finding the quantities of earthwork, foundation and walls in a building whose walls have the same section.

#### Procedure
1. Find the **total centre-line length** of all the walls (main and partitions), measured along the middle of the walls.
2. **Deduct** for the junctions where walls meet: each T-junction takes away half of the width of the wall (the part counted twice); a cross-junction deducts the same on each side, i.e. it counts as two T-junctions.
3. Multiply the corrected length by the width and the depth of each section (trench, PCC, footing, plinth masonry, superstructure).

#### Formula
$$
L_{corrected} = L_{total} - n \times \frac{b}{2}
$$
where $n$ is the number of T-junctions (a cross-junction counts as two) and $b$ the width of the wall at that level.

#### Example
For a room 4 m x 3 m (clear) with a 0.23 m wall: $L = 2(4.23 + 3.23) = 14.92$ m. A partition with two T-junctions would deduct $2 \times 0.23/2 = 0.23$ m. The trench volume = $14.92 \times 0.9 \times 1.0 = 13.43$ m³.

#### Merits and limits
It is fast and simple, and suited to uniform rectangular buildings; it is not accurate where the wall sections differ, for which the long wall-short wall method is used.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. In the centre line method, what length is first found?
   A. Total outer perimeter only
   B. Total centre-line length of all walls, measured along the middle of the walls
   C. Total of clear room lengths
   D. Length of the longest wall
   Answer: B. The corrected length is then multiplied by width and depth. (Key point: Procedure)

2. How are junctions handled?
   A. Each junction adds the wall width
   B. No correction is needed
   C. Each T-junction deducts half the wall width from the total length (L = Ltotal - n x b/2)
   D. Each junction deducts the full wall height
   Answer: C. The part at a junction would be counted twice. (Key point: Junction deduction)

3. A partition with two T-junctions on a 0.23 m wall deducts:
   A. 0.115 m
   B. 0.46 m
   C. 2 m
   D. 0.23 m
   Answer: D. 2 x 0.23/2 = 0.23 m. (Key point: Example deduction)

4. When is the centre line method not accurate?
   A. When the wall sections differ; the long wall-short wall method is then used
   B. For uniform rectangular buildings
   C. For single-room buildings
   D. When trench depth is 1 m
   Answer: A. It suits uniform walls only. (Key point: Limitation)

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