Concrete Mix Calculator

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. It is designed for UK homeowners, DIY users, self-builders, renovators and tradespeople planning small to medium concrete jobs.

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

Start by entering the required finished concrete volume. In metric mode, enter cubic metres (m³). In imperial mode, enter cubic feet (ft³). The calculator automatically converts cubic feet to cubic metres internally. Enter the compacted, finished concrete volume rather than adding together the loose volumes of the dry materials.

Next, choose the mix ratio. The available presets are 1:2:4, 1:1.5:3, 1:2.5:4 and 1:3:6, expressed as cement: sand: coarse aggregate by volume. A custom option lets you enter your own positive proportions for all three components.

Choose the material method that matches how you intend to buy the aggregate. Select Cement, sand and aggregate for separate quantities, or Cement and ballast when using a combined sand-and-stone ballast product. In ballast mode, the calculator combines the calculated sand and aggregate weights into one ballast figure.

Select a cement bag size of 20 kg, 25 kg, 30 kg or 40 kg, or enter a custom bag size. The default is 25 kg. Set the waste allowance between 0% and 50%; the calculator starts at 5% to cover spills, handling losses and small measuring differences.

In Advanced mode, choose a water-to-cement ratio of 0.45, 0.50 or 0.55, or enter a custom value between 0.20 and 1.00. The standard mode uses 0.50. Water should still be added gradually because the moisture already present in sand and aggregate affects the amount needed on site.

You can also choose a mixer working capacity of 80, 90, 120, 140 or 160 litres, or enter a custom working capacity. Use the practical batch capacity, not the total drum volume. When a capacity is supplied, the calculator rounds the number of batches up to a whole number and divides all materials evenly between those batches.

For an optional cost estimate, enter any known price per cement bag and price per tonne for sand, aggregate or ballast. Blank price fields are ignored. The estimate covers only the entered supplier prices and does not include delivery charges or minimum order rules.

Results Explanation

The Materials Required section shows whole cement bags, sand and aggregate or ballast, plus estimated water. Cement is always rounded up to the next whole bag so the displayed shopping quantity is sufficient for the calculated requirement.

The Mix Details section confirms the adjusted finished volume, selected ratio, purchasing method, waste allowance, dry material volume, cement weight and total material weight. Material quantities are displayed in standard UK purchasing units such as bags, kilograms, tonnes and litres, even when the input volume was entered in cubic feet.

Where prices have been entered, the cost breakdown shows the estimated cost of each applicable material and an estimated total. In ballast mode, sand and aggregate costs are replaced by the ballast cost.

Where a mixer capacity has been selected in Advanced mode, the batch plan shows the number of batches, finished concrete per batch and the cement, sand, aggregate or ballast, and water required for each batch.

For adjusted concrete volumes of 1 m³ or more, the calculator also displays a ready-mix notice. This is a planning prompt rather than a price comparison: larger pours may be more practical to order as ready-mixed concrete than to mix in small batches.

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 fixed densities in the supplied calculator logic: 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

related calculators

Concrete Footing Calculator – Estimate concrete volume, bags required and material cost for strip, pad and round post footings.
Concrete Driveway Calculator – Estimate concrete volume, sub-base material and material cost for driveway projects.
Screed Calculator – Estimate screed volume, material quantities and coverage for floor levelling and renovation projects.
Concrete Stairs Calculator – Estimate concrete volume, bag quantities, ready-mix concrete and material cost for steps, staircases and landing pads.
Concrete Ramp Calculator – Calculate concrete volume, slope ratios, MOT Type 1 requirements and material costs for concrete ramps.
Concrete Block Fill Calculator – Estimate concrete or grout volume, block count and bags required for concrete block walls.
Concrete Weight Calculator – Estimate concrete weight from dimensions or known volume, including reinforcement, material cost and load limit checks.
Postcrete Calculator – Estimate the Postcrete volume, whole bags and total weight required to set fence posts.
Concrete Column Calculator – Estimate concrete volume, ready-mix, concrete bags, weight and material costs for circular, square, rectangular and tapered concrete columns.
Self-Levelling Compound Calculator – Estimate self-levelling compound volume, bags required, mixing water and material cost for floor levelling projects.
Low Carbon Concrete Calculator – Estimate the embodied carbon of concrete projects, compare different concrete mixes and calculate potential carbon savings.
Kerb & Edging Concrete Calculator – Estimate concrete volume, concrete bags required and material cost for kerb and edging installations.
Concrete Drying & Curing Calculator – Estimate concrete curing milestones, drying times and project dates based on slab thickness and site conditions.
Rebar Calculator – Estimate the quantity, total length, weight and stock bars required for a rectangular reinforcement grid.
Concrete Bags Calculator – Calculate how many bags of concrete you need, including wastage, total weight, supplied volume, leftover concrete and estimated material cost.
Concrete Calculator – Estimate concrete volume, bags required and material cost for slabs, pads, piers and post holes.

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.