Concrete calculator
Enter the pour dimensions and a nominal mix to get cement bags, sand, aggregate and water — with the dry-volume factor stated, not buried.
| Breakdown | Value |
|---|
Estimate. The method and sources are on this page — check them against your own case before you act.
How it is calculated
Concrete is ordered by wet volume but batched from dry materials. The dry-volume factor bridges the two, and the mix ratio splits that dry volume into cement, sand and aggregate.
Wet volume = L × W × D × (1 + extra) · Dry volume = wet × 1.54 · Cement bags = dry × cement part ÷ sum of parts ÷ 0.0347
Measure the pour
Length × width × depth in metres gives the wet volume. Add 3–5% for spillage, an uneven base or a slab that is thicker at one end.
Convert wet to dry
Dry materials bulk up: the standard factor is 1.54, so 1 m³ of wet concrete needs 1.54 m³ of dry cement, sand and aggregate combined.
Split by the mix ratio
In 1:1.5:3 the parts total 5.5, so cement is 1 ÷ 5.5 of the dry volume. Dividing by 0.0347 converts cement volume to 50 kg bags, and the water is 0.50 × cement weight.
Nominal mixes and standard factors
| Nominal mix | Grade | Typical use | Cement per m³ (approx.) |
|---|---|---|---|
| 1 : 3 : 6 | M10 | Mass concrete, levelling course | 4.4 bags |
| 1 : 2 : 4 | M15 | Lightly loaded footings, boundary walls | 6.4 bags |
| 1 : 1.5 : 3 | M20 | RCC slabs, beams and columns in homes | 8.1 bags |
| 1 : 1 : 2 | M25 | Higher-grade RCC, water-retaining work | 11.1 bags |
| Dry-volume factor | 1.54 | Converts wet volume to dry material volume | — |
| One cement bag | 50 kg = 0.0347 m³ | Cement at 1,440 kg/m³ | — |
| Water-cement ratio | 0.45–0.55 | IS 456 limit for normal exposure | — |
What most pages get wrong
1 m³ of concrete is not 1 m³ of materials
Sand and aggregate bulk up when dry, so 1 m³ of wet concrete needs about 1.54 m³ of dry material. Skipping the factor underprices every order by a third.
About 8 bags fill a cubic metre of M20
The 1:1.5:3 mix uses roughly 8.1 bags of 50 kg cement per cubic metre. Stronger mixes use more cement, not more sand.
More water is weaker concrete
The water-cement ratio is capped at 0.50 for M20 in normal exposure under IS 456. Extra water makes placing easier and strength lower — never add water to loosen a mix that has started to set.
The table is a site estimate, not a design
Nominal mixes are not permitted for structural work above the grades they cover. For slabs, columns and footings, use the design mix and cube test results from your engineer.
Frequently asked questions
How many cement bags are needed for 1 m³ of M20 concrete?+
What is the dry-volume factor 1.54?+
How much sand and aggregate for a 150 mm slab of 5 × 4 m?+
Can I use this calculator for a design mix?+
Why is the water shown in litres?+
How much extra should I order for a slab?+
Sources, dates and a changelog.
Every number this calculator uses is either an input you control or a value from the sources below. The formula is compiled and tested at build time, so the page cannot ship with a broken calculation.
Sources
This page
- Last verified: 29 October 2026
- Next review: 29 April 2027
- Vertical: Construction & Real Estate
- Build tests: 4 passed
- Changelog: 1 entry
How we handle errors
- Spotted a mistake? Report it — we correct and log it.
- Corrections appear in the changelog below.
- Read the methodology and the disclaimer.