Concrete Mix Calculator
Calculate the cement, sand, aggregate, ballast and water needed to produce a chosen volume of concrete.
- Mix ratios are treated as volumetric proportions of cement, sand and coarse aggregate.
- The calculation applies a dry-volume conversion because loose ingredients occupy more space than finished concrete.
- Material weights use estimated bulk densities and may vary with moisture, grading and supplier.
- Cement bags are rounded up to the next whole bag for the materials list.
- Ballast combines the estimated sand and aggregate quantity. Actual ballast composition varies between suppliers.
- Water is a starting estimate and should be added gradually.
- Structural concrete should follow the specified professional mix design rather than a general volumetric ratio.
Use this concrete mix calculator to estimate how much cement, sand, coarse aggregate, ballast and water you need for a chosen finished volume of concrete.
Enter the finished concrete volume in cubic metres or cubic feet, choose a standard or custom mix ratio, select your cement bag size and add a waste allowance. The calculator then converts the required finished volume into dry material quantities, rounds cement up to whole bags and presents sand, aggregate or ballast in practical purchasing units.
Advanced mode can also estimate water using a chosen water-to-cement ratio, divide the mix into practical mixer batches and calculate an indicative material cost from the supplier prices you enter.
PRO TIP: Measure the pour area carefully and keep a small contingency, but avoid relying on an excessive waste percentage to compensate for uncertain dimensions. For slabs, paths and bases, calculate volume from consistent finished dimensions and check for variations in excavation depth before ordering materials. For a continuous pour, organise all materials, tools and labour before mixing so each batch can be placed without avoidable delays.
How to Use this concrete mix calculator
Work from the finished volume of concrete required for the pour rather than the loose volume of the individual ingredients. If you only have the project dimensions, calculate the concrete volume first. If you don’t already know the finished concrete volume, use our concrete calculator to calculate it from your project dimensions first.
Select the cement:sand:aggregate ratio specified for the job and choose whether you’re buying sand and coarse aggregate separately or using ballast. Cement bag size and a small allowance for site losses can then be included in the estimate.
Where the amount of mixing water is required, Advanced Mode uses the selected water-to-cement ratio to estimate it from the cement quantity. Treat this as a starting quantity because moisture already present in the aggregates affects how much additional water is needed.
For concrete mixed on site, you can also enter the mixer’s working capacity to divide the materials into batches. Supplier prices can be added separately to estimate the material cost.
Results Explanation
The results show the required cement bags, sand and aggregate or ballast, estimated water and total material weight. Cement is rounded up to whole bags.
If supplier prices are entered, the calculator also shows the estimated material cost. Advanced Mode can produce a batch plan based on the mixer’s working capacity, including the quantity of each material required per batch.
For adjusted volumes of 1 m³ or more, a ready-mix notice is shown as a prompt to consider whether mixing the concrete on site remains practical.
How the Maths Works
The calculator first increases the entered finished volume by the selected waste allowance:
Adjusted finished volume = entered volume × (1 + waste percentage ÷ 100)
It then multiplies that adjusted volume by 1.54. This dry-volume factor allows for the reduction in volume that occurs when loose dry ingredients are mixed and compacted.
Dry material volume = adjusted finished volume × 1.54
The dry volume is split according to the chosen cement: sand: aggregate ratio. For a 1:2:4 mix, for example, there are seven total parts. Cement receives 1/7 of the dry volume, sand 2/7 and aggregate 4/7.
Each component volume is converted to weight using the calculator’s assumed densities: cement 1,440 kg/m³, sand 1,600 kg/m³ and aggregate 1,500 kg/m³. Ballast is calculated as the combined sand and aggregate weight.
Water is estimated from the cement weight and the selected water-to-cement ratio:
Water in litres = cement weight in kg × water-to-cement ratio
Because one litre of water is treated as one kilogram, the same numeric value is used for water litres and water weight. Cement bags are calculated by dividing the cement weight by the selected bag size, then rounding up to the next whole bag.
If mixer capacity is used, the adjusted finished volume is converted to litres and divided by the chosen working capacity. The batch count is rounded up, then each material quantity is divided by that number of batches.
Cost estimates multiply whole cement bags by the entered bag price. Sand, aggregate and ballast weights are divided by 1,000 to convert kilograms to tonnes, then multiplied by the entered price per tonne.
Common Mistakes to Avoid
- Entering loose material volume instead of the required finished concrete volume.
- Confusing a ratio such as 1:2:4 with percentages rather than parts by volume.
- Using the mixer drum’s total volume instead of its safe working capacity.
- Assuming the water estimate is exact without allowing for moisture in the aggregates.
- Forgetting to round cement up to whole bags when buying materials.
- Mixing ballast and separate sand-and-aggregate prices in the same estimate.
- Ignoring delivery fees, bulk-bag sizes, minimum order quantities or supplier rounding.
- Using a general mix estimate for structural work without a suitable specification or professional advice.
faqs
What concrete mix ratio should I use?
The correct ratio depends on the job and the required concrete performance. The calculator provides several common volumetric ratios, but it does not determine whether a mix is suitable for a particular structural or exposure requirement. Follow the project specification, product guidance or advice from a competent professional. If you also want to compare the embodied carbon of different concrete mixes, use our low-carbon concrete calculator.
How much extra concrete should I allow for waste?
The calculator defaults to 5%. A modest allowance can cover spills, handling losses and small measurement differences. Irregular excavations or uncertain depths may justify a larger allowance, but accurate measuring is better than adding a large arbitrary margin.
How much water should I add to concrete?
The calculator estimates water from the cement weight using a water-to-cement ratio. Standard mode uses 0.50, while Advanced mode offers 0.45, 0.50, 0.55 or a custom value. Add water gradually because damp sand and aggregate already contain moisture.
Does the calculator work in cubic feet?
Yes. Select Imperial and enter the finished volume in cubic feet. The calculator converts it to cubic metres internally using 35.3146667 cubic feet per cubic metre, while material outputs remain in UK purchasing units.
Does the cost estimate include delivery?
No. It includes only the cement bag and per-tonne material prices you enter. Delivery charges, minimum order quantities, bulk-bag rounding and supplier-specific fees are excluded.
Is hand mixing practical for one cubic metre of concrete?
The calculator displays a ready-mix prompt at an adjusted volume of 1 m³ or more. Whether site mixing is practical depends on access, labour, mixer capacity, placement time and supplier availability. Larger continuous pours are often easier to manage with ready-mixed concrete. If you’re considering premixed concrete bags instead of mixing cement, sand and aggregate separately, use our concrete bags calculator to estimate the number of bags required.
Can I use this calculator for structural concrete?
It can estimate quantities from the selected assumptions, but it does not design a structural mix or confirm strength, durability or compliance. Structural concrete should follow the engineer’s specification and any applicable project and Building Regulations requirements.
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disclaimer
This calculator provides planning estimates based on the dimensions, ratios, densities, wastage and prices entered. Actual material requirements can vary because of measurement accuracy, aggregate grading, moisture content, compaction, site losses, supplier packaging and mixing practice.
The water result is an estimate, not an instruction to add the full amount immediately. Add water gradually and avoid making the mix wetter than required, as excess water can reduce concrete quality.
The calculator does not specify concrete strength, exposure class, reinforcement, slab thickness, foundations or structural suitability. For structural, load-bearing, retaining, foundation or regulated work, use the project specification and obtain advice or sign-off from an appropriately qualified professional where required.
Wear suitable personal protective equipment when handling cement and concrete. Wet cement is alkaline and can cause serious skin and eye injury. Follow the manufacturer’s safety information, control dust and keep cement products away from children.
Prices are indicative only. Confirm current product sizes, stock, delivery charges, minimum orders and final quantities with the supplier before purchasing.