This concrete calculator allows you to estimate how much concrete you need for a specific area and how many bags of concrete are required for this space, accounting for concrete density, weight, and spillage. Concrete is often sold in bags. If you know the size of a bag (it should say how much concrete you’ll get out of it on the bag), our calculator will help you find the amount of bags you need to buy. This way, you can also estimate the concrete slab cost.

### Concrete definition

Nowadays, concrete is one of the most common materials used globally in construction. It is composed of fine and coarse aggregate bound together in a fluid cement (cement paste) that hardens over time. Aggregates are usually sand and gravel (or crushed stone), while the paste is water and Portland cement. Portland cement is not a brand name — that is the generic term for the type of cement used in basically all concrete (like how stainless is a type of steel). Through a process called hydration, the cement and water harden and bind the aggregates into a mass similar to a rock. After 28 days, concrete achieves around 99% of maximal compressive strength. However, this hardening process continues for years, resulting in stronger concrete over time.

Are you a contractor embarking on a project? Our sand calculator and this gravel calculator will help you to figure out how much of each material you will need for your building site.

### Why use the concrete calculator?

You may have been in a situation similar to this: you have decided to build your own house, a terrace, or a fence. You go to a shop, buy X bags of concrete, and, pleased with yourself, you get to work right away. Somewhere in the middle, you realize you have only one bag left. Irritated, you go back to the shop, buy another batch of concrete, go back, start working again, and then… it’s not enough. Again. The day’s already over, the shop is closed, work’s not done, and tomorrow you need to go back to the shop again. Only this time, annoyed, you buy much more, and by the end of the project, you’re left with half of all these extra bags of concrete with absolutely no use for them. You wasted time, you wasted money, and it most certainly got on your nerves. All of this could have been easily avoided with assistance from our concrete calculator. You’ll never have to wonder, “how much concrete do I need?” again.

### Construction of a building out of concrete slabs

How much concrete do I need?

First, you need to estimate the volume of concrete that you need. Provide the dimensions (length, width, and height) and quantity of your concrete slabs or an area that you want to pave.

Determine the weight of all of those elements — this is how bagged concrete is sold; they tell you how much the concrete from the bag will weigh (for example, you’ll get 60 pounds of concrete out of one bag). Given the volume we just calculated and the concrete’s density (again, you’ll find this info on the bag; we provided a common value, but it varies), you can calculate the weight of all your elements.

Provide the size of the bag so we can find out how much concrete is produced per bag.

Finally, you can provide the waste ratio — how much you think you will lose via spillages, defective elements, and other unfortunate events. Now you know how many bags you truly need.

All dimensions are given in feet by default. You can change them to any other unit by simply unlocking the field (the padlock button).

### An example calculation

So let’s say we have 4 concrete elements, each 3 feet long, 3 feet wide, and 3 feet high. Now we multiply 4 times (3×3×3). Pre-mixed concrete is usually sold by the cubic yard, and this unit is used by default. As construction elements are usually measured in feet, our concrete calculator converts the volume into cubic yards — in our example, 4 cu yd (108 cubic feet). To learn more about cubic yards, visit our cubic yard calculator.

Sometimes, you’ll know how many slabs you need. Other times, you’ll just know the area that needs to be paved – feel free to provide any of these values. In our example, we are paving 36 square feet.

Once we have the above measurements, we can get to the essence of the matter.

Check if the density of the concrete from a particular producer is the same as the default value in our calculator (150 lb/cu ft). Feel free to change it as needed.

Now, the total weight of concrete you need is shown.

Check if the weight of a single bag of concrete is the same as the default already given (60 lb). If not, again, change it to the appropriate number.

To be safe, account for spillage and waste. Experienced contractors usually assume 5-10%.

In our example, let’s leave the default measures. We need 4 cubic yards of concrete; our producer sells concrete in bags weighing 60 lb with a 150 lb/cu ft density. The total weight of concrete that we need is 16,201.03 lb. Assuming 5% is lost to waste and spillage — voila! We need 284 bags of concrete.

### Concrete slab cost

Our concrete calculator makes working the cost of a concrete slab easy. Once you know how much concrete you need (in bags) and how many slabs you’ll produce out of it, simply provide the price of the bag, and you’ll receive the concrete slab cost, a cost to pave your desired area, cost per unit of volume and the total cost of the material you need.