Concrete Calculator
Enter your measurements to find out how much concrete to order or how many bags to buy.
Your measurements
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Check your order
Your concrete order
- Use the project’s specified dimensions and concrete product; this estimate does not design a slab or specify its strength.
- Check the actual mixed yield per bag, or the supplier’s ready-mix order unit. Add your allowance only once.
- Confirm any reinforcement, formwork and delivery requirements from the project specification; follow the product’s mixing instructions.
Tools for this job
Verify the form dimensions before ordering. For finishing, match the tool and timing to the mix and intended surface, including any slip-resistant texture.
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- Spread and smooth compatible materials
Finishing trowel
MARSHALLTOWN MXS64D finishing trowel
A steel finishing trowel to consider for spreading and smoothing work. Follow the material instructions for tool choice and timing; some finishes need a different float or surface texture.
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Short tape measure
STANLEY 25-foot tape measure
For checking lengths, widths and short runs before ordering. This is a 25-foot tape; use matching units in the calculator and check the scale on the selected model.
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Already have suitable tools? Reuse them. These are optional product suggestions, not a complete equipment list or a hands-on comparison. Amazon may redirect Amazon.com links to local products or search results. Amazon.nl links search for alternatives, which may differ in brand, size and specification. Check suitability, seller, delivery and any import costs on your chosen store before ordering.
How to calculate concrete volume
Concrete is bought by volume, so every calculation comes down to length × width × depth, in consistent units. The mistakes happen in the conversion: a 100 mm slab is 0.1 m, not 100, and a 4 inch slab is 0.333 ft.
Switch the calculator to imperial and it converts to cubic yards automatically, which is how ready-mix is ordered in the US. One cubic yard is 0.7646 cubic metres, or 27 cubic feet.
The formulas
Worked example
For a quantity example, take a patio 5 m × 3 m with a specified 100 mm thickness. V = 5 × 3 × 0.1 = 1.5 m³. A selected 10% allowance gives 1.65 m³. These dimensions illustrate the arithmetic; they do not specify a suitable patio design.
In generic estimate mode, a 25 kg bag yields 0.0117 m³ (11.7 litres), so 1.65 ÷ 0.0117 rounds up to 142 bags, weighing 3,550 kg in total. If your product label instead states 12 litres per 25 kg bag, select product yield and enter 25 kg and 12 litres: the same job needs 138 bags. Compare actual bag and delivery quotes, access and handling before choosing how to supply the pour.
Bags versus ready-mix
The table uses the calculator's generic yield estimate, using 0.764554858 m³ per cubic yard. Counts use the unrounded yield, so rounding a displayed value before dividing can change a whole-bag order. These figures are not manufacturer pack specifications: use the actual label yield for your selected bag.
For ready-mix, ask the supplier about minimum loads, order increments, part-load charges, access and unloading. The calculator shows a quarter-unit rounding option; it does not establish the supplier's sales terms.
| Bag size | Yield | Bags per m³ | Bags per cubic yard |
|---|---|---|---|
| 20 kg | 9.36 L | 107 | 82 |
| 25 kg | 11.7 L | 86 | 66 |
| 27.2 kg (about 60 lb) | 12.7296 L | 79 | 61 |
| 36.3 kg (about 80 lb) | 16.9884 L | 59 | 46 |
| 40 kg | 18.72 L | 54 | 41 |
Separate-material quantity estimates
These figures use the same approximate dry-volume factor and bulk densities as the calculator. For example, 1:2:3 has six total parts: 1 × 1.54 ÷ 6 × 1,440 = 369.6 kg of cement before allowance.
Select a ratio only when it matches an appropriate project mix specification. The table estimates quantities; it does not assign a strength class, specify structural suitability or replace a supplier's mix design.
| Ratio | Estimated cement | 25 kg cement bags, rounded up |
|---|---|---|
| 1 : 1.5 : 3 | 403.2 kg | 17 |
| 1 : 2 : 3 | 369.6 kg | 15 |
| 1 : 2 : 4 | 316.8 kg | 13 |
| 1 : 2.5 : 5 | 260.9 kg | 11 |
| 1 : 3 : 6 | 221.8 kg | 9 |
Which thickness should I enter?
Enter the slab, footing or hole dimensions specified for your project. The shape and depth fields calculate volume only: the default depth is an example, not a recommendation for every patio, driveway or foundation.
Ground conditions, loads and the chosen construction system belong in the project design. Confirm thickness, sub-base, reinforcement and concrete specification before using that design to estimate an order.
Use the product instructions for water
Read the water requirement and mixing sequence on the chosen bag or its current data sheet. The linked QUIKRETE 1101 sheet gives its own water quantities by bag size; that guidance applies to that product, not every concrete mix.
This calculator does not estimate mixing water from total bag weight or cement weight. For separate materials, use the specified mix design and its water requirements, together with its placement and curing instructions.
Sources and assumptions
Concrete volume follows the selected shape dimensions. Bag counts divide that volume, including the allowance, by the entered product yield or a clearly labelled generic estimate of 0.468 L/kg. The reference tables use the same calculation. Separate-material quantities use an approximate 1.54 dry-volume conversion and stated bulk densities.
- QUIKRETE Concrete Mix 1101: technical data sheet: The manufacturer gives approximate yields of 8.5 L for 40 lb, 12.7 L for 60 lb and 17 L for 80 lb of this concrete mix, with water instructions for each bag size. These are product-specific figures, not a universal yield or water recipe.
Before using this estimate
- In product mode, enter the yield and weight for the same bag; both fields stay in litres and kilograms in either measurement system. The generic conversion and separate-material estimates are not verified recipes for every brand, and the calculator does not prescribe mixing water.
- This calculator estimates quantities; it does not design slab thickness, reinforcement, foundations or strength. A cement-to-sand-to-aggregate ratio does not establish a strength class. Use the project specification for load-bearing work.
Source notes reviewed . See how we check calculations and handle corrections.
Planning your order
Check the inputs before buying: measure the surfaces you need, then apply an allowance and round to whole packs. The guides include worked examples you can follow alongside this calculator.
Published by OrderEnough. This is a planning estimate: check the product specification and the assumptions above before ordering. Last updated . Read how we source our figures on the methodology page.