Ready Mixed Cement 'vs' Concrete - What's the difference?

How much concrete do I need?

Concrete is a composite material composed of aggregates (fine and coarse materials) bonded together by cement.

Are you working on a new DIY project? Knowing the right quantity of materials for your project construction can be quite difficult. Regardless of the scale of your projects, using the wrong quantity of materials could mess up the quality of your work. This article will provide tips to ensure you use the right quantity of concrete by answering the age-old question “how much concrete do I need for my project?”

Why should I calculate the quantity of concrete needed for my project?

  1. Prevents wastage: It is important to have an idea of the right quantity of concrete to use or at least a range before construction begins. This will ensure that you only buy what you need and wastages after construction will be minimal.
  2. Money-saving: A proper plan made to prevent wastage will reduce costs to the barest minimum and save money that would have otherwise been used to purchase materials that would end up wasted.
  3. Assists in the preparation of budgets: Before construction begins on the site, there must be adequate planning and organization of all schedules, materials, equipment, and manpower. The financial and material budgets need an estimated figure of the estimated quantity and price of concrete to be used for construction. This can only be done when an estimate has been calculated.
  4. Avoidance of unnecessary time delays and stress: Having an estimate of concrete to use will ease the process of ordering concrete on the site. There would be fewer problems associated with over-ordering and under ordering of concrete, and a reorder period can easily be set.

Factors that would influence this …

  • The size of the site: The size of the site plays the biggest role during construction. It is usually the basic determinant for how much material will be used or how long the construction process would take.
  • Type of concrete you want to use: Concrete is usually sold in bags or by the yard. Bagged concrete is sold in small bags and is suitable for small-scale projects. However, if you’re involved in a larger construction, it is better to buy by the yard.

Steps to calculate how much concrete you need …

  1. Determine how thick you would like your finished project.
  2. Take an accurate measurement of your site area.
  3. Determine the square foot by multiplying the length and width of your measurement.
  4. Convert your desired thickness from inches to feet.
  5. Multiply the thickness in feet by the square footage to get your cubic feet.
  6. Multiply this value by 0. 037 to convert to cubic yards


It is important to put all these figures and conversion rates into relatable context.

Assuming you want to build a 12 by 12 feet concrete slab, let’s follow the steps for calculating the amount of concrete you need.

  1. Assume the thickness to be 4inches.
  2. The area is measured as 12 by 12 feet
  3. The square footage is 144 (12 multiplied by 12)
  4. 4 inches converted to feet is 0.33 ( 4 divided by 12)
  5. The cubic feet is 47.52 ( 144 multiplied by 0.33)
  6. The cubic yard is 1.76 ( 47.52 multiplied by 0.037)

Alternatively, you could make use of concrete calculators. Online concrete calculators can be used to value the amount of concrete you need. They can help save you from arithmetic and conversion problems.

Number of concrete bags to purchase …

Now that you know how much you need, there’s a need to convert that value to the quantity of bags. There are two methods to do this:

Method 1

Divide the total cubic yards by the yield (volume of fresh batch-produced concrete expressed in cubic meters).  The yield is calculated by dividing the total mass of the material by the measured density of freshly mixed concrete.

Method 2

Make use of this laid-down conversion rate.

  • A forty-pound bag yields 0.011 cubic yards.
  • A sixty-pound bag yields 0.017 cubic yards.
  • An eighty-pound bag yields 0.022 cubic yards.


Although it is easy to forget to calculate the volume of concrete you need before you begin your project, it is an indication of a lack of planning and organisation. It is strongly advised to take that step before the construction begins.