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Enter the job shape and dimensions to estimate concrete volume, whole bags, ready-mix volume, waste, and rough cost.

Concrete estimate
Unit system
Shape
Slab

Choose the shape closest to the concrete you are ordering. Structural sizing still needs local code or project drawings.

Dimensions
m
m
mm
Ordering options
Supply mode
Bag size
25 kg
EUR
%
Currency
EUR
Result
Estimate only
Bags to buy
106Bags
Order volume
1.32m3
Estimated cost

Add a price to estimate cost.

Measured volume
42.38 ft3 / 1.20 m3
With waste
1.73 yd3 / 1.32 m3
Total bag weight
2,650 kg
Formula
length x width x thickness x quantity
order volume = measured volume x (1 + waste / 100)
Shape diagram
Result for Slab
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Concrete estimating guide

This tool is for ordering material, not for designing the structure. It is useful for early takeoffs, shopping lists, and quick comparisons between bags and ready-mix.

How to use it

  1. Choose the closest shape: slab, footing, wall, post hole, or tube.
  2. Enter the measured dimensions. Keep long lengths in feet or meters and small thicknesses in inches or millimeters.
  3. Set the quantity when the same shape repeats, such as several post holes.
  4. Add a waste factor. Ten percent is a common starting point for rough estimating, but your job may need more or less.
  5. Choose bags or ready-mix and enter a price if you want a rough cost.

What the estimate includes

The calculator finds geometric concrete volume, adds your waste factor, and then converts the result to bags or ready-mix volume.

Slabs, footings, and walls
Rectangular volume is length times width times thickness or depth.
Post holes
The tool can subtract the volume taken by a round post inside the hole.
Tube forms
A tube or ring is calculated as the outside cylinder minus the inside cylinder.
Bags
Bag counts are rounded up because partial bags cannot be bought.

Practical examples

Patio slab

A 12 ft by 10 ft slab at 4 in thick is 40 ft3 before waste. With 10% waste and 80 lb bags, it needs 74 bags.

Fence post holes

Four 12 in holes, 36 in deep, with 4 in posts use about 8.38 ft3 before waste.

Small footing trench

A 30 ft footing that is 16 in wide and 8 in deep is about 26.67 ft3 before waste.

Common mistakes

Mixing feet and inches

Length and width use feet in imperial mode, while slab thickness, diameters, and trench depth use inches.

Forgetting waste

Uneven ground, form gaps, spillage, and supplier rounding can leave you short if you order the exact measured volume.

Using the wrong bag yield

The preset yields are common estimates. Product labels and data sheets are the better source for the exact bag you buy.

Treating volume as design advice

The calculator does not choose slab thickness, reinforcement, footing size, frost depth, or soil bearing values.

Tips

Check both units

The result shows cubic yards and cubic meters so you can compare your estimate with a supplier's preferred unit.

Use custom yield for local bags

If bags are sold by kilograms or liters in your area, choose custom yield and enter the package coverage.

Save each scenario

Save a bagged estimate and a ready-mix estimate before changing dimensions or waste.