How to Calculate CFT for Sand and Aggregate in India

What is CFT in Indian Construction?

CFT stands for Cubic Feet, which is a unit of volume defined as the space occupied by a cube measuring one foot on each side. The standard equivalence is:

• 1 CFT = 1 foot × 1 foot × 1 foot
• 1 CFT = 0.0283 cubic metres (CUM)
• 1 Brass = 100 Cubic Feet (CFT)

In Indian construction logistics, large supply trucks are typically categorized by the number of brass they can carry. For instance, a small tipper holds 1 to 1.5 brass (100–150 CFT), while large multi-axle dumper trucks carry 3 to 5 brass (300–500 CFT). Understanding these metrics prevents discrepancies during unloading.

How to Calculate CFT of a Truck or Tipper

To calculate the volume of sand or aggregate delivered to your site in a transport vehicle, you must measure the internal dimensions of the truck's cargo bed. Use a standard steel measuring tape and measure the length, width, and height of the filled material in feet. The formula is:

CFT = Length (ft) × Width (ft) × Height (ft)

If any measurement is in inches, you must convert it to decimal feet by dividing by 12. For example, if a truck bed measures:

• Length: 12 feet 6 inches = 12.5 feet
• Width: 6 feet 0 inches = 6.0 feet
• Height: 3 feet 4 inches = 3.33 feet

Apply the calculation: CFT = 12.5 × 6.0 × 3.33 = 249.75 CFT.

To convert this to brass, divide by 100: 249.75 ÷ 100 = 2.50 brass.

Conversion Guide Table

Here is a reference table for converting construction volume units:

How to Calculate Sand Needed for a Room

To calculate the amount of sand needed for plastering or flooring, you must determine the surface area and the planned thickness of the mortar layer. The standard formula for wet volume is:

Wet Volume = Length × Width × Thickness

However, dry sand shrinks when mixed with cement and water. To compensate, engineers apply a dry volume multiplier of 1.33. For example, to lay a 2-inch screed bed for floor tiles in a room measuring 15 ft × 12 ft:

• Area = 15 × 12 = 180 sq ft
• Thickness = 2 inches = 2 ÷ 12 = 0.166 feet
• Wet Volume = 180 × 0.166 = 30 CFT
• Dry Volume Needed = 30 × 1.33 = 39.9 CFT (approx. 40 CFT of sand).

Density and Weight of Sand & Aggregate

If you need to verify the material weight because your supplier invoices by metric tonnes instead of volume, use the standard material density constants:

• Dry River Sand: Density ≈ 1,600 kg per cubic metre, or 45.3 kg per CFT.
• Wet/Damp Sand: Density ≈ 1,900 kg per CUM, or 53.8 kg per CFT.
• Coarse Aggregate (Grit/Stone): Density ≈ 1,550 kg per CUM, or 43.9 kg per CFT.

Therefore, 1 brass of dry sand (100 CFT) weighs approximately 4,530 kg (4.53 metric tonnes). Knowing this conversion is crucial when checking weight slips at weighbridges.

Common Site Mistakes and Fraud Prevention

• Mistake 1: Not leveling the truck cargo bed: Suppliers often heap the sand in the center, making the load appear larger. Always level the material flat before measuring height.
• Mistake 2: Measuring external truck dimensions: Measure only the internal boundaries of the truck container where the sand sits.
• Mistake 3: Ignoring moisture bulking: Wet sand occupies up to 20-30% more volume than dry sand due to moisture films pushing grains apart. This is called bulking of sand. Always factor in dampness.
• Mistake 4: Accepting empty space at the bottom: Check if there are raised platforms, tires, or wooden planks hidden underneath the sand load.