Quantity Estimation of Brickwork and Concrete with Worked Examples
Estimating is one of the first jobs given to a fresh civil engineer. A client or contractor wants to know how many bricks to order, how many bags of cement, and how many cubic metres of sand and aggregate. Errors cost money directly. This article shows the standard method of estimating material quantities for brick masonry and for concrete, with worked examples you can repeat for any wall or slab.
Units and Basic Rules
Indian Standard IS 1200 lays down the method of measurement for building works. Brickwork and concrete are measured in cubic metres, plastering and flooring in square metres, and steel in kilograms or tonnes. Dimensions are usually taken to the nearest 0.01 m. Openings such as doors and windows are deducted from masonry, subject to the rules in the standard.
| Constant | Value used | Reason |
|---|---|---|
| Volume of one cement bag | 0.0347 m³ | 50 kg / 1440 kg/m³ |
| Dry volume factor, mortar | 1.33 (sites use 1.27 to 1.33) | Voids in sand and bulking |
| Dry volume factor, concrete | 1.54 (sites use 1.52 to 1.57) | Voids between aggregate particles |
| Modular brick with joint | 200 x 100 x 100 mm | 190 x 90 x 90 mm brick + 10 mm mortar |
| Wastage of bricks | About 5 % | Breakage and cutting |
The dry volume factors exist because wet concrete or mortar occupies less volume than the loose dry materials that go into it. Water fills voids, and fine particles fill the gaps between coarse particles. For example, to make 1 m³ of wet concrete you need about 1.54 m³ of loose dry ingredients.
Brickwork Estimation
Volume of one brick with mortar = 0.20 x 0.10 x 0.10 = 0.002 m³ Number of bricks per m³ = 1 / 0.002 = 500 Volume of bricks alone in 1 m³ = 500 x 0.19 x 0.09 x 0.09 = 0.7695 m³ Wet mortar per m³ of brickwork = 1 - 0.7695 = 0.2305 m³
In practice, frog filling and uneven joints raise the mortar requirement a little, so some estimators round wet mortar up to about 0.25 to 0.30 m³ per m³. The worked example below uses the calculated value to keep the steps clear.
Worked example: brick wall in 1:6 mortar
A wall is 5.0 m long, 3.0 m high and 200 mm thick, built with modular bricks in cement mortar 1:6. It has one door of 1.0 m x 2.1 m.
Step 1: Net volume Gross volume = 5.0 x 3.0 x 0.20 = 3.00 m³ Door = 1.0 x 2.1 x 0.20 = 0.42 m³ Net volume = 3.00 - 0.42 = 2.58 m³ Step 2: Bricks Bricks = 2.58 x 500 = 1290 Add 5 % wastage = 1290 x 1.05 = 1355 bricks Step 3: Mortar Wet mortar = 2.58 x 0.2305 = 0.595 m³ Dry mortar = 0.595 x 1.33 = 0.791 m³ Step 4: Cement and sand for 1:6 Sum of ratio = 1 + 6 = 7 Cement = 0.791 / 7 = 0.113 m³ = 0.113 / 0.0347 = 3.26 bags -> say 3.5 bags Sand = 0.791 x 6 / 7 = 0.678 m³
Concrete Estimation
For a nominal mix C : FA : CA, the dry volume is divided in proportion to the ratio. Cement volume is converted to bags using 0.0347 m³ per bag.
Dry volume = wet volume x 1.54 Cement (m³) = dry volume x C / (C + FA + CA) Sand (m³) = dry volume x FA / (C + FA + CA) Aggregate = dry volume x CA / (C + FA + CA)
Worked example: RCC slab in M20 (1:1.5:3)
A roof slab is 4.0 m x 5.0 m and 125 mm thick, cast in nominal mix 1:1.5:3.
Wet volume = 4.0 x 5.0 x 0.125 = 2.50 m³ Dry volume = 2.50 x 1.54 = 3.85 m³ Sum of ratio = 1 + 1.5 + 3 = 5.5 Cement = 3.85 / 5.5 = 0.700 m³ = 0.700 / 0.0347 = 20.2 bags Sand = 3.85 x 1.5 / 5.5 = 1.050 m³ Aggregate = 3.85 x 3 / 5.5 = 2.100 m³
Round cement up to 21 bags. Steel for the slab is estimated separately from the bar bending schedule. Water is usually not estimated as a material but is roughly 0.5 times the mass of cement for a nominal mix.
Quick reference per cubic metre
| Mix | Cement (bags/m³) | Sand (m³/m³) | Aggregate (m³/m³) |
|---|---|---|---|
| 1 : 1.5 : 3 (M20) | 8.07 | 0.42 | 0.84 |
| 1 : 2 : 4 (M15) | 6.34 | 0.44 | 0.88 |
| 1 : 3 : 6 (M10) | 4.44 | 0.46 | 0.92 |
| 1 : 4 : 8 (M7.5) | 3.41 | 0.47 | 0.95 |
These values follow directly from the 1.54 dry volume factor. For example, for 1:2:4 the sum is 7, so cement is 1.54 / 7 = 0.22 m³, which is 0.22 / 0.0347 = 6.34 bags.
Preparing the Abstract
After the detailed measurement sheet, an abstract of materials collects totals from all items. For the wall and slab above:
| Material | Brick wall | RCC slab | Total | Order |
|---|---|---|---|---|
| Bricks (nos.) | 1355 | - | 1355 | 1400 |
| Cement (bags) | 3.26 | 20.2 | 23.5 | 24 |
| Sand (m³) | 0.678 | 1.050 | 1.728 | 1.8 |
| 20 mm aggregate (m³) | - | 2.100 | 2.100 | 2.2 |
Common Mistakes
- Forgetting the dry volume factor, which underestimates material by about a third.
- Using modular brick numbers when the site uses traditional bricks of a different size; recompute bricks per m³ from the actual size.
- Not deducting openings, lintels and RCC bands from brickwork volume.
- Ignoring bulking of damp sand when sand is ordered by volume.
Summary
Brickwork with modular bricks needs 500 bricks and about 0.23 m³ of wet mortar per cubic metre. Convert wet mortar and wet concrete to dry volume using factors of about 1.33 and 1.54, divide by the sum of the mix ratio, and convert cement volume to bags at 0.0347 m³ each. A clear measurement sheet followed by an abstract keeps estimates accurate and easy to check.