How this calculator works
A rectangular pour measuring 5 m × 4 m × 0.15 m has a geometric volume of 3 m³. At the default 5% allowance, plan for 3.15 m³.
- Step 1Measure the pour5 × 4 × 0.15 mUse length, width and thickness for a rectangular pour.
- Step 2Find the volume3 m³Multiply the dimensions after converting them to metres.
- Step 3Add allowance3.15 m³Apply the wastage percentage you selected.
Choose metres, centimetres, feet or inches. The calculator converts every measurement to metres before calculating. For a round column, it uses the circular area formula instead of multiplying three rectangular dimensions.
What the result includes
- Geometric volumeA rectangular slab, footing or wall section, or one cylindrical column.
- Wastage allowanceAn editable percentage added to the net volume for ordering.
- Optional material estimateBag equivalents when you enter the product yield, or approximate ingredients for a selected nominal mix.
Worked example
- Net rectangular volume
length × width × thickness- Order quantity
net volume × (1 + wastage % ÷ 100)- Unit conversion
convert dimensions to metres before multiplying
- lengthlonger side 5 m
- widthsecond side 4 m
- thicknessdepth of the pour 0.15 m
- Net volume5 × 4 × 0.153 m³
- Wastage3 × 5%0.15 m³
- Estimated order volume3 × 1.053.15 m³
The code keeps full precision. Displayed values are rounded to a few decimal places, so very small pours may show as zero in some units. Use the cubic-metre figure and confirm the supplier’s ordering increment.
Optional material quantities
The material estimate is separate from the concrete volume. You can leave the nominal mix set to “No material estimate” if your engineer or supplier has specified a different mix.
For a selected traditional nominal ratio, the calculator multiplies order volume by an approximate 1.54 dry-volume factor.
It then divides that dry volume by the selected cement:sand:aggregate ratio. For a 1 m³ M20 example, this gives an estimated 0.28 m³ of cement, 0.42 m³ of sand and 0.84 m³ of aggregate.
Cement bag equivalents use a 50 kg bag and an assumed cement bulk density of 1,440 kg/m³. The calculator also states an approximate 0.0347 m³ per bag for the volume-based bag estimate.
These are assumptions, not a universal product yield. The other bag count stays blank until you enter a manufacturer’s yield.
- Dry volume estimate
wet order volume × 1.54- Ratio total
1 + 1.5 + 3 = 5.5 parts- Each ingredient
dry volume × its parts ÷ total parts
- Dry ingredient volume1 × 1.541.54 m³
- Cement1.54 × 1 ÷ 5.50.28 m³
- Sand1.54 × 1.5 ÷ 5.50.42 m³
- Aggregate1.54 × 3 ÷ 5.50.84 m³
M20 1:1.5:3 and M15 1:2:4 are shown as traditional nominal mixes commonly cited in estimating examples.
This page could not verify those proportions or the 1.54 factor against accessible standard text, so it does not claim they comply with IS 456 or IS 10262. Nominal proportions are not a project mix design.
Reading your result
The net volume is the measured geometry. The order volume includes your selected allowance. Cubic feet and cubic yards are equivalent unit conversions of that order volume.
Bag equivalents mean order volume divided by the yield you entered. They are not automatically rounded up to whole bags because bag yields vary. Check the product label and supplier’s minimum order increment.
Other building estimates
Concrete is usually one line in a bigger build. Walls, floors and finishes each need their own quantities.
For walls, the brick calculator estimates bricks and wet mortar. Floors and walls take tiles and grout from the tile calculator, and the paint calculator works out litres for a room.
For volumes of other shapes, such as tanks, use the volume calculator.
Common mistakes
Mistake: Entering inches while the unit is set to feet.
Instead: Choose one unit for every dimension, and check it beside each field.
Mistake: Entering the radius of a round column.
Instead: The cylinder field asks for the full diameter across the centre.
Mistake: Treating the wastage allowance as a guarantee of sufficient concrete.
Instead: Ground conditions, leakage and placement can change actual needs; confirm quantities with the supplier.
Mistake: Treating a nominal mix estimate as a structural specification.
Instead: Use the mix approved for the actual materials and project requirements.
Assumptions and limits
The estimate does not account separately for irregular shapes, stairs, reinforcement displacement, voids, sloping subgrades, formwork leakage, concrete pump losses, aggregate moisture or bulking. A single user-editable wastage percentage cannot predict these conditions.
It also does not determine concrete strength, workability, exposure class, water-cement ratio, curing needs, reinforcement or structural safety. Those require project-specific professional judgement.
- Not structural designNo load, strength or reinforcement checks are performed.
- Product-specific bagsEnter the concrete bag yield from the product documentation.
- Confirm before orderingCompare dimensions, allowance and mix with an engineer or supplier.
Sources and methodology
Rectangular volume uses the cuboid side-length product. Cylindrical volume uses circular base area times height, as described by Math Is Fun.
The cuboid volume example and cylinder formula show these equations.
NIST is the reference for the exact inch definition and SI volume units. The 1.54 multiplier, 1,440 kg/m³ cement density and 0.0347 m³ bag volume are stated assumptions, not standard requirements verified for a particular product.
A copy of IS 456:2000 is linked below as background for concrete practice. This tool does not attribute a specific clause, mix table or ratio to that standard. The accessible copy could not be text-extracted during preparation of this draft.
Frequently asked questions
How much concrete do I need for a rectangular slab?
Multiply length by width by thickness after converting each dimension to the same unit. Add the allowance you choose. The calculator also shows the net volume before that allowance.
Does it calculate a round column?
Yes. Enter the full diameter and height. It calculates circular area, π × radius², then multiplies by height.
Can I enter inches or centimetres?
Yes. Choose metres, centimetres, feet or inches, then enter every active dimension in that unit. The calculation converts those values to metres first.
What does the wastage percentage mean?
It is an extra amount added to the measured volume to help estimate an order. The default is 5%, but site conditions differ. Ask your supplier or engineer what allowance fits your job.
How many concrete bags will I need?
Enter the bag’s stated cubic-metre yield. The calculator divides order volume by that yield. It does not assume all bagged concrete products have the same yield.
Are M20 and M15 mix quantities exact?
No. They are rough estimates based on traditional nominal ratios and the stated dry-volume assumption. They do not replace a designed mix or a specification for your project.
Does this check whether a footing, wall or column is safe?
No. It only estimates geometric volume and optional material quantities. It does not check loads, soil, reinforcement, strength or structural design.
Safety note
Estimate only. Confirm dimensions, mix proportions and required concrete quantity with an engineer or concrete supplier before ordering or construction. Do not use this calculator for structural design.
About this tool
By Nitin Raturi. Last reviewed 22 Oct 2026. Read the methodology and source notes. See the change log.
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