Free tool
Concrete calculator: cement, sand & aggregate
Estimate the cement, sand and aggregate for a concrete slab, beam or column in Bangalore. Enter the size and mix, get quantities instantly.
How it works
We take the wet concrete volume from your dimensions, apply the standard dry-volume factor of 1.54, then split it by the mix ratio to give cement bags, sand and aggregate. Add 5 to 10 percent for wastage before ordering.
Common concrete mixes
- M20 (1:1.5:3) for slabs and general RCC work
- M15 (1:2:4) for flooring and non-structural work
- M25 (1:1:2) for columns and heavily loaded members
Why the dry volume is 1.54 times the wet volume
Your slab dimensions give the wet volume, meaning the space the finished concrete will occupy. But dry cement, sand and aggregate contain air voids between the particles, and mixing with water fills those voids and compacts everything. So you always have to buy more dry material than the finished volume suggests. The standard allowance is a dry factor of 1.54, and this tool applies it before splitting the total by your chosen mix ratio.
Cement is then converted to 50 kg bags, and sand and aggregate are shown in cubic feet, which is how they are ordered locally. An approximate tonnage is also given, because tipper loads are often discussed by weight.
Which mix goes where
| Grade | Nominal ratio | Commonly used for |
|---|---|---|
| M7.5 | 1:4:8 | Levelling course, mass filling, non-structural work |
| M10 | 1:3:6 | Plain concrete bedding below footings, flooring base |
| M15 | 1:2:4 | Plain concrete, kerbs, light non-structural elements |
| M20 | 1:1.5:3 | The usual grade for residential slabs, beams and columns |
| M25 | 1:1:2 | More heavily loaded columns and elements where specified |
Nominal mix is a rule of thumb, not a design
Worth being straight about this. Ratios like 1:1.5:3 are volumetric conventions that work reasonably on small sites. They are not a substitute for a design mix, where proportions are calculated from the actual materials and tested for strength. For any structural element, the grade to use is your structural engineer’s decision, and on larger pours ready-mixed concrete from a batching plant gives far more consistent results than site mixing by volume.
The other variable that matters as much as the proportions is the water-cement ratio. Adding extra water makes concrete easier to place and measurably weaker, and it is the most common quiet compromise on a site. If a pour looks soupy, that is worth a conversation.
Curing decides the strength you actually get
Concrete gains strength through hydration, not by drying out. Slabs need to be kept continuously damp, commonly for at least seven days and preferably longer. Skipped curing in a Bangalore summer is a leading cause of surface cracking and of concrete never reaching its specified strength, and it costs almost nothing to do properly.
What this estimate excludes
- Reinforcement steel, which is calculated separately with the steel calculator
- Formwork, centring and props
- Wastage, so add 5 percent or so when ordering
- Admixtures, pumping charges and labour
Frequently asked questions
What mix should I use for a roof slab?
M20 is the grade most commonly specified for residential slabs, which is why it is the default here. Treat that as context rather than instruction: your structural engineer specifies the grade for your design, and some elements will call for M25 or higher.
Site mixed or ready mix?
For a small pour, site mixing is practical. For a full slab, ready-mixed concrete is usually better: proportions are batched by weight, the mix arrives consistent, and the pour finishes faster, which matters because a slab should ideally be cast in one continuous operation. Access is the constraint, so check a transit mixer and pump can reach your site.
Can I use less cement to save money?
Not on structural concrete. The saving is small and the consequence is a permanent reduction in the strength of something holding your house up. If cost is the concern, the honest levers are the design itself and the finishes, not the concrete grade.