Estimate cement, sand and aggregate for slabs, footings, PCC and other concrete work.
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Cement Concrete Calculator: Free Online Tool
The Cement Concrete Calculator estimates how much cement, sand and coarse aggregate you need for a concrete job such as a slab, footing, plinth or floor base. You enter the length, width and thickness, the number of identical items and the mix ratio, and it returns the wet volume, the dry volume and the quantity of each material.
Site engineers, contractors, estimators and students use this type of calculation before ordering material. Ordering too little stops the pour halfway and creates a cold joint, while ordering too much wastes money and storage space. A quick, consistent estimate also makes it easier to compare quotations and to plan labour and mixer capacity for the day of casting. The tool works in feet and inches or in metres and millimetres, so it suits both older site practice and metric drawings, and every result can be rechecked by hand. The result is only as good as the dimensions you enter, so measure carefully.
When to use this calculator
Use this calculator when you are preparing a material order for a roof slab, a lintel, a footing, a plinth beam base or a floor screed. It is also useful at the tender stage, when you need a quick cost estimate from drawing dimensions. Students can use it to check hand calculations in estimating assignments. On site, it helps you decide how many bags of cement to stock before a pour and how much sand and stone to ask the supplier to deliver. You can repeat the calculation for different mixes, such as M15 and M20, to compare cement consumption.
How to use the Cement Concrete Calculator
- Open the calculator above on your phone, tablet or computer. Nothing needs to be installed and no sign-up is required.
- Choose the unit system first (feet / inches or metres / mm). The input labels change to match your choice.
- Pick the option you need from the drop-down list (M5 (1:5:10); M7.5 (1:4:8); M10 (1:3:6); M15 (1:2:4); M20 (1:1.5:3); M25 (1:1:2); ...).
- Enter your values in the input boxes: Length (ft), Width (ft), Thickness (inches), Number of items, Concrete mix, Cement, Sand, Aggregate, Dry volume factor, Wastage (%). The boxes already hold sample values, so overwrite them with your own.
- Press Calculate. The result appears straight away under the button.
- Change any value and press Calculate again to compare options. Press Reset to go back to the sample values.
- Check the result against your drawings, project specification and local code before you order material or approve work.
How the calculation works
The calculator first finds the wet volume: length x width x thickness x number of items, increased by the wastage percentage (default 0%). Dry volume is the wet volume multiplied by the dry volume factor, which is 1.54 by default, because loose dry materials shrink when they are mixed with water. The dry volume is then divided in the ratio of the mix. For 1:1.5:3, cement is 1/5.5 of the dry volume. Cement is converted to 50 kg bags using 1440 kg/m³, and sand and aggregate are shown in m³ and cft. Dry factor, wastage and the ratio can be edited. Results are estimates only.
Worked example
When you open the page the calculator is filled with sample values. Pressing Calculate with those values gives the result below, which you can use to check that you are reading the output correctly.
| Concrete volume | |
|---|---|
| Wet volume | 1.416 m³ (50.00 cft) |
| Dry volume (wet x 1.54) | 2.180 m³ (77.00 cft) |
| Materials | |
| Cement | 11.4 bags (50 kg) = 571 kg |
| Sand | 0.595 m³ (21.00 cft) |
| Coarse aggregate | 1.189 m³ (42.00 cft) |
Tips and common mistakes
- Check that all dimensions use the unit system selected at the top, because mixing feet, inches and metres is the most common input error.
- Keep the dry volume factor at 1.54 unless your engineer or local specification gives another value; changing it directly changes every material quantity.
- Add a realistic wastage percentage for spillage, uneven excavation and over-break. The default is 0%, so the result is the theoretical quantity only.
- Remember that sand and aggregate are bulk materials. Confirm the supplier's unit, whether cft, m³ or truck load, before converting the estimate into an order.
- Choose the mix from the structural drawing. Do not select M20 or M25 for structural work simply because it gives a comfortable cement quantity.
Frequently asked questions
What is the dry volume factor and why is it 1.54?
Dry materials occupy more space than the compacted wet concrete they produce. The calculator multiplies wet volume by 1.54 to get the dry volume of cement, sand and aggregate. You can edit this factor if your specification says otherwise. Edit it only when your engineer gives another value.
How many bags of cement are in one cubic metre of concrete?
It depends on the mix. For 1:2:4, the calculator takes wet volume x 1.54 x (1/7) and divides by 0.0347 m³ per 50 kg bag, which gives about 6.3 bags per m³ of wet concrete. Check the figure against your own mix design before ordering cement.
Which mixes can I select?
You can choose M5 (1:5:10), M7.5 (1:4:8), M10 (1:3:6), M15 (1:2:4), M20 (1:1.5:3) or M25 (1:1:2). A custom ratio option lets you type your own cement, sand and aggregate parts. Pick the mix that your drawing or specification asks for, not the cheapest one.
Does this calculator include steel reinforcement or formwork?
No. It only calculates concrete volume and the cement, sand and aggregate quantities. For reinforcement steel quantity, use the RCC calculator, which adds steel based on kilograms per cubic metre of concrete. Steel, formwork and curing must be estimated separately.
Is the result accurate enough for ordering?
It is a good estimate, but not a final quantity. Real jobs have wastage, uneven surfaces and variation in material bulking. Add a wastage percentage and confirm final orders with your engineer. Always keep some margin when placing the final order.
Important note
This tool gives estimates for planning, study and quick checks. It does not replace design by a qualified engineer, site-specific testing, or the requirements of your project specification and local building code. Always confirm final quantities, test results and acceptance limits with the responsible engineer before using them for construction or payment.
