Concrete Volume Calculator
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By Abdul HadiReviewed by Dr. James Mitchell, PE (Structural Engineering)Published: Updated:
References
- [1]Portland Cement Association, Design and Control of Concrete Mixtures, 16th ed., 2016.
- [2]American Concrete Institute, ACI 318-19: Building Code Requirements for Structural Concrete. https://www.concrete.org/store/productdetail.aspx?ItemID=318U19
- [3]UK Concrete, UK Concrete - Specifying Sustainable Concrete. https://www.ukconcrete.org/specifying-sustainable-concrete
How to Use?
- 1
Select what to calculate
Choose from Concrete Volume, Bags Needed, or Material Quantities. The input fields adjust automatically for your selection.
- 2
Choose the shape
Select Slab for rectangular pours or Column for cylindrical pours like fence posts and round footings.
- 3
Enter dimensions in any unit
Type in the length, width, and thickness (or height and diameter for columns). Use the unit dropdowns to switch between metres, feet, inches, or centimetres.
- 4
Set the waste factor
Enter a waste percentage (5–10% recommended) to account for spillage, compaction, and uneven subgrades. The adjusted volume shows how much concrete you should actually order.
- 5
Select the mix ratio (materials mode)
In Materials mode, pick your mix ratio – 1:2:3 for general construction, 1:1.5:3 for structural elements, or 1:3:6 for lean fill.
- 6
Review the results
The calculator displays volume with and without waste, bag counts for three bag sizes, and (in relevant modes) ready-mix truck loads or cement/sand/aggregate quantities.
- 7
Check alternative units
The primary volume result shows in your chosen unit with alternative cubic foot and cubic yard values listed below for convenience.
Worked Examples
1Patio slab – 5 m × 4 m × 0.1 m
Given Values
Calculate:volume
Shape:slab
Length / Height:5
Width / Diameter:4
Thickness / Depth:0.1
Waste Factor:10
Results
Volume Without Waste:2
60 kg Bags:72
2Column – 4 fence posts, 0.3 m diameter, 0.6 m deep
Given Values
Calculate:volume
Shape:column
Length / Height:0.6
Width / Diameter:0.3
Waste Factor:10
Results
Volume Without Waste:0.17
60 kg Bags:7
3Garage foundation – 6 m × 8 m × 0.15 m with waste
Given Values
Calculate:volume
Shape:slab
Length / Height:6
Width / Diameter:8
Thickness / Depth:0.15
Waste Factor:10
Results
Volume Without Waste:7.2
60 kg Bags:258
4Bags from known volume – 3 m³ target
Given Values
Calculate:bags
Target Volume:3
Waste Factor:10
Results
Volume Without Waste:3
60 kg Bags:108
5Material quantities – 1:2:3 mix for 1 m³
Given Values
Calculate:materials
Shape:slab
Length / Height:5
Width / Diameter:2
Thickness / Depth:0.1
Mix Ratio (Cement : Sand : Aggregate):1:2:3
Waste Factor:10
Results
Volume Without Waste:1
Cement:264
sandKg:528
aggregateKg:792
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Frequently Asked Questions
A 40 kg bag yields approximately 0.018 m³, a 50 kg bag yields 0.022 m³, and a 60 kg bag yields 0.028 m³. You need about 56 bags of 40 kg, 45 bags of 50 kg, or 36 bags of 60 kg per cubic metre. These values are approximate and vary by manufacturer, so always check the coverage printed on the bag you purchase.
Add 5–10% to the calculated volume. For small DIY projects like fence posts, use 10% because mixing and placing conditions are less controlled. For large commercial pours with experienced crews, 5% is usually sufficient. The calculator applies the waste factor automatically when you enter a percentage in the Waste Factor field.
No, this calculator estimates concrete volume only. The space taken by reinforcement bars is negligible for most residential and commercial applications, typically displacing less than 2% of the volume. For heavily reinforced structural elements, a structural engineer should verify whether a volume deduction is needed.
Yes. Fresh concrete contains air voids that must be removed by vibration or rodding. Uncompacted concrete can have 5–20% void content. The waste factor partially accounts for this. On site, ensure proper vibration to achieve full compaction, which improves both strength and durability.
For volumes under 0.5 m³, bagged concrete is usually more economical. For volumes over 3 m³, ready-mix is almost always cheaper. Between 0.5 and 3 m³, price both options because minimum delivery charges may affect the comparison. This calculator provides volume in cubic metres and bag counts for three bag sizes to help you compare.
The standard mix ratio is 1:2:3 (one part cement, two parts sand, three parts aggregate by volume), which produces a C20 concrete with roughly 20 MPa compressive strength at 28 days. This is suitable for most residential applications including driveways, footings, and floor slabs. For structural elements, use 1:1.5:3 (C25) or specify a higher grade through a ready-mix plant.
A nominal mix uses fixed volume ratios (such as 1:2:3) and is suitable for small projects where precise strength is not critical. A design mix is specified by the required strength grade (such as C30) and proportioned by weight in a batching plant to achieve that strength with the exact materials available. Design mixes are required for all structural applications under building codes.
The water-to-cement (w/c) ratio is the weight of water divided by the weight of cement in the mix. A w/c ratio between 0.40 and 0.60 is typical. Lower ratios produce stronger, more durable concrete but are harder to work with. Never add extra water on site to improve workability, as it weakens the concrete. Use a plasticiser admixture instead.
Standard reinforced concrete weighs approximately 2,400 kg per cubic metre (150 lb/ft³). This includes the weight of cement, sand, aggregate, water, and typical reinforcement. Lightweight concrete using expanded clay or shale aggregates weighs around 1,600–2,000 kg/m³. The weight matters for formwork design, transport, and structural loading calculations.
Concrete can be poured in cold weather with precautions. The hydration reaction slows below 10°C and stops below 5°C. If fresh concrete freezes, it can lose 50% or more of its potential strength. Use heated mixing water, accelerators, or insulating blankets for winter pours. Never pour concrete onto frozen ground, as thawing will cause settlement cracking.
Concrete reaches roughly 65% of its 28-day strength at 7 days and about 85% at 14 days. The full design strength is assumed at 28 days. Keep concrete moist for at least 7 days after pouring using wet burlap, plastic sheeting, or a curing compound. In hot weather, start curing as soon as the surface can withstand it.
Calculate each step as a small slab: tread depth × riser height × stair width. Multiply by the number of steps and add the landing volume separately. For 12 steps with 0.28 m treads, 0.18 m risers, and 1.0 m width, the total is about 0.55 m³ plus approximately 0.3 m³ for the landing. Use the slab mode for each element and sum the results.
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