1. Your construction

Choose what you are building, then enter its planned dimensions.

2. Shape and dimensions

Start with a template or draw your area. Points and lengths remain editable on the plan.

Thickness (cm)

Use the thickness specified for your construction. Soil, use, loads and reinforcement matter: this tool does not design the structure.

Editable example, not a recommended thickness.

3. Concrete quantity

Enter the required information to see the concrete quantity.

Allowance (%)

Allow for waste, uneven ground and measurement uncertainty. The suggested 5% is an editable example, not a requirement.

4. How will you source the concrete?

Copy the weight and yield from your bag. Concrete yield in litres is not the bag weight in kg.

Your concrete bags

Bag weight (kg)

Manufacturer yield (L)

5. Shopping / order list

Enter the required information to see the concrete quantity.

6. Estimated cost

Enter my prices — optional

Price per concrete bag (€)

Subtotal of provided prices: Not provided

Enter my prices — optional

Estimate labour

Tick to add your rate or quotation. No labour rate is assumed.

Only provided prices are counted. A blank field does not mean a product is free. Check delivery charges too.

9. View calculation details

Area × thickness in metres = volume. 100 cm = 1 m; 1 m³ = 1,000 L. The allowance is added to theoretical volume. Bag counts are rounded up.

Mix and water quantities are indicative. Aggregate moisture and required strength need a suitable mix design. This tool does not certify structural concrete.

Preparing a screed?

A screed prepares a surface for flooring; it does not replace a load-bearing slab. The existing screed mode is retained for projects, with an editable mortar example without aggregate.

How is volume converted to bags?

Raw volume is area multiplied by thickness converted to metres.

The selected allowance is added and the volume is converted to litres.

Bag count is rounded up using the product’s actual yield.

Formula

Bags = ceiling((volume in m³ × 1,000) ÷ bag yield in litres).

Worked example

For 0.24 m³, or 240 L, with a yield of 12 L per bag: 240 ÷ 12 = 20 bags.

Check before purchasing

The exact yield printed on the bag.
That premixed concrete already includes binder and aggregates.
Actual mixing capacity and working time for larger volumes.

Frequently asked questions

Is a cement bag the same as a concrete bag?

No. Premixed concrete is a complete dry mix; cement is only one constituent.

Why are so many bags needed?

A bag yield is only a few litres compared with a slab volume measured in cubic metres.

What you get

Calculate concrete volume and allowance for a slab, patio or footing for free. Plan a delivery, premixed bags or cement, sand and aggregate for site mixing.

How to use it

Enter only the requested values and check the unit shown beside each field. The main result gives the figure to use first. Details explain conversions, secondary quantities and rounding. Change any value to compare another situation without starting again.

Before using the result

Measure the finished area and use the coverage or pack size stated on the product you will buy. An allowance helps cover cuts and waste, but does not replace the manufacturer’s instructions.

How many concrete bags for a slab?