Concrete Calculator
Fast, accurate and free online betonu calculator tool running directly in your browser.
-
1Enter data
Enter content, paste text or load a file from disk. -
2Click the button
The tool will immediately process your data in the browser. -
3Get the result
Copy the finished text or save the file to your device.
return "Result ready in 0.1s";
}
Rate this tool:
Related tools
Other tools you may find usefulHow does the concrete calculator work and why is it worth using?
Concrete calculator is an advanced online tool created for investors, builders and DIY enthusiasts planning construction works. Accurately estimating the amount of concrete mix needed is a key stage of planning any investment - from pouring a small foundation for a fence post, to large foundation, ceiling or terrace slabs. Ordering too little concrete results in costly downtime on the construction site and the need to order refills, which significantly increases transport costs. In turn, excess material is a waste of money and a problem with its disposal.
Our tool allows you to precisely calculate the volume of concrete expressed in cubic meters (m³), its estimated mass (weight) in tons and kilograms, as well as the approximate cost of the entire screed. Additionally, the calculator provides an approximate dry mix recipe based on the selected proportions of ingredients (cement, sand, gravel and water) and indicates how many bags of cement (weighing 25 kg or 50 kg) should be purchased to prepare concrete on the construction site yourself.
How to calculate the amount of concrete for different shapes?
Depending on the project being implemented, concrete elements may take on various geometric shapes. Our calculator supports the two most popular ones:
1. Cuboid (slabs, foundations, walls, terraces)
To calculate the volume of a rectangular slab or wall, three key dimensions are needed:
- Length:total longitudinal dimension of the screed.
- Width:transverse dimension.
- Thickness or height:planned depth of the screed.
The mathematical formula for the volume of a cuboid is:
Volume (V) = Length × Width × Thickness
All these dimensions must be expressed in the same units (e.g. meters) so that the final result corresponds to cubic meters (m³).
2. Cylindrical or column (round columns, footed columns, circles)
For elements with a circular cross-section, such as load-bearing columns or foundation footings, to calculate the volume we need:
- Diameter:width of the circular cross-section of the column.
- Height (depth):vertical length of the column.
The formula for the volume of a cylinder is:
Volume (V) = π × R² × Height
WhereRis the radius of the section (half the diameter), andπ(Pi) is a mathematical constant of approximately 3.14159.
Concrete reserve for losses – why is 10% the standard?
When pouring concrete, in practice there is always some loss of material. They may result from several factors:
- Unevenness of the ground (e.g. the ground is not perfectly level, which makes the screed thicker in some places).
- Deflection of formwork under the weight of liquid concrete.
- Mix residues on the walls of the concrete mixer, in the concrete pump or wheelbarrows.
- Natural shrinkage of concrete during the setting and drying process.
For this reason, professional contractors always add a so-called waste margin. Typically, it isfrom 5% to 10%. In the case of difficult ground or complex formwork, it is recommended to add up to 15% allowance. Our calculator allows you to automatically take this value into account in the final result.
Concrete classes and mixture proportions (recipe for 1 m³)
Depending on the purpose of the structure, different concrete strength classes are used. They differ in the proportions of cement, sand and gravel used. The following classes are standardly used:
| Concrete class (old / new marking) | Proportion (Cement : Sand : Gravel) | Purpose |
|---|---|---|
| B7.5 / B10 (C8/10) - lean concrete | 1 : 3 : 4 | Leveling screeds, foundation pads, terraces on the ground. |
| B20 (C16/20) - standard concrete | 1 : 2 : 3 | Ceilings, foundation strips, stairs, lintels, load-bearing terraces. |
| B25 (C20/25) - strong concrete | 1 : 1.5 : 2.5 | Load-bearing structures exposed to higher loads, columns, ring beams. |
The water/cement ratio (W/C) determines the density and strength of concrete. Typically, the optimal ratio of water weight to cement weight is from 0.45 to 0.55. Too much water weakens the concrete, causing it to crack, while too little makes it difficult to place and compact the mixture.
How to calculate the number of bags of cement and the weight of the ingredients?
The average density of traditional concrete is approximately2400 kg/m³. This means that one cubic meter of ready, wet concrete weighs almost 2.5 tons! If you plan to prepare the mixture yourself at the construction site using a concrete mixer, you must purchase the appropriate amount of dry ingredients. For example, for a standard proportion of 1:2:3, one cubic meter of concrete requires approximately:
- Cement:approx. 350 kg (i.e. 14 bags of 25 kg or 7 bags of 50 kg).
- Sand:approx. 700 kg.
- Gravel (aggregate):approx. 1050 kg.
- Water:approx. 175 liters (at W/C ratio = 0.5).
Our tool automatically calculates these values for the volume you specify, taking into account the selected inventory. This allows you to quickly prepare a shopping list at the construction warehouse and avoid logistical problems.
Frequently asked questions (FAQ)
How to calculate how much concrete is needed for a terrace slab?
To calculate the amount of concrete for a (rectangular) terrace, measure its length and width in meters and thickness in centimeters. Then multiply the length × width × (thickness / 100). For example, a terrace measuring 5 m × 4 m and 10 cm thick requires 5 × 4 × 0.1 = 2 m³ of concrete. We recommend adding a 10% allowance for losses, i.e. ordering 2.2 m³.
How much does 1 m³ (cubic) of concrete weigh?
The average weight of one cubic meter (so-called cube) of traditional ready-mix concrete is approximately 2,400 kg (2.4 tons). The exact mass depends on the type of aggregate used and the degree of mixture compaction. Lightweight concrete may weigh from 1,200 to 1,800 kg/m³, while heavy concrete may exceed 3,000 kg/m³.
How many 25 kg bags of cement are needed for 1 m³ of concrete?
For the most popular class of concrete C16/20 (B20) prepared in proportions 1:2:3, approximately 350 kg of cement is used to make 1 m³ of concrete. This means that exactly 14 bags of cement weighing 25 kg (or 7 bags of 50 kg) are needed. The rest of the volume is filled with sand, gravel and water.
How much concrete should be added when ordering from a concrete plant?
Typically, a safety margin of 5% to 10% of the calculated volume is added. This reserve covers dimensional inaccuracies in the excavation or formwork, deflection of the formwork under the pressure of concrete and the remains of the mixture that will remain in the pump and transport lines.
What proportion of cement to sand is best for foundations?
For pouring footings and foundation footings, the most commonly used concrete is class C16/20 (formerly B20) with the volume proportions of ingredients 1:2:3 (1 part of cement, 2 parts of sand, 3 parts of gravel) or class C20/25 (B25) with proportions of 1:1.5:2.5. Do not use lean concrete (B7.5/B10) for foundations, which only serves as a base.