Concrete Mix Calculator
Work out cement, sand and aggregate quantities for a given mix ratio and concrete volume.
Concrete Mix Calculator
Work out cement, sand and aggregate quantities for a given mix ratio.
Calculating A Concrete Mix By Ratio
Concrete mix ratios describe the proportion of cement to sand to aggregate by volume — for example, a 1:2:4 ratio is a common general-purpose mix, 1:1.5:3 is used for structural elements needing higher strength, and 1:2:3 suits pavement applications. This calculator converts your target concrete volume and chosen ratio into the actual quantities of each dry material needed.
The first step accounts for shrinkage: dry, loose materials take up more space than the finished wet concrete, so dry volume = wet volume × 1.54 is used to size the total dry material required. That dry volume is then split across the ratio — for a 1:2:4 mix, the total parts are 1+2+4=7, so cement gets 1/7 of the dry volume, sand gets 2/7, and aggregate gets 4/7. Cement volume is then converted to weight using a bulk density of 1,440 kg per cubic metre, and divided by 20 to estimate standard 20 kg bags.
What Information You Need To Enter
Enter the concrete volume you need in cubic metres, and select a mix ratio — general purpose (1:2:4), structural (1:1.5:3), or pavement (1:2:3).
Understanding Your Results
You will see the dry volume required after the shrinkage factor, along with the cement, sand and aggregate volumes, cement weight, and an estimated bag count. This is most useful for smaller hand-mixed or site-batched pours; larger pours are typically ordered as ready-mixed concrete from a batching plant to a specified strength grade.
Why Accurate Estimating Matters
Getting your mix quantities right avoids running short of cement or aggregate mid-batch, and helps you compare the cost of site-mixing materials yourself against ordering ready-mixed concrete for larger pours.
Frequently Asked Questions
What mix ratio should I use?
General purpose (1:2:4) suits most non-structural residential applications like paths and slabs. Structural elements such as footings or reinforced slabs typically need a stronger 1:1.5:3 mix, and pavement or driveway applications often use 1:2:3. Always confirm the specified strength grade with your engineer for structural work.
Why is dry volume higher than wet volume?
Dry cement, sand and aggregate contain air gaps between particles that close up once mixed with water and compacted, so more dry material is needed by volume than the finished wet concrete volume. The 1.54 factor accounts for this.
Is this calculator suitable for large pours?
It is most useful for smaller, hand-mixed or site-batched jobs. For larger pours, ready-mixed concrete delivered to a specified MPa strength grade is generally more practical and consistent -- see our Concrete Volume and Concrete Cost calculators for that approach.
How many 20 kg cement bags come in a standard delivery?
This varies by supplier. This calculator estimates the number of 20 kg bags based on the cement weight required for your mix, which you can compare against your supplier's packaging options.
Does this account for water content?
No -- water content depends on the workability required and is typically added according to supplier or manufacturer guidance for your specific mix and application.
Related Calculators & Services
Need An Exact Price, Not Just An Estimate?
The Concrete Mix Calculator gives you a fast, useful planning figure. For a fixed, accurate price backed by a site assessment, request a free professional quotation from HPL Construction.
