A wet concrete volume and a pile of loose ingredients are different quantities. The Whatson Cement & Concrete Mix Calculator keeps that difference visible by applying an editable dry volume factor before dividing material proportions.
The ratios are entered by volume. The default 1:2:4 proportion and 1.54 dry factor are estimating assumptions, not a recommendation for a structural element. Use the specified mix or supplier information for the work you intend to do.
What the calculation actually does
The tool adds the ordering allowance to the entered wet concrete volume. It then multiplies by the dry factor. Cement, sand and aggregate receive their shares of that dry volume according to the parts you enter.
Cement volume is multiplied by the entered loose cement density to estimate kilograms. Bag count is then rounded up. Sand and crush remain loose volumes and are shown in cft.
Follow this batch example
Enter 100 cft of wet concrete, a 5% allowance, parts of 1 cement, 2 sand and 4 aggregate, a dry factor of 1.54, 50 kg bags and a loose cement density of 1,440 kg/m³.
| Material | Checked requirement |
|---|---|
| Cement mass | 941.93 kg |
| Whole cement bags | 19 |
| Loose sand | 46.20 cft |
| Loose crush | 92.40 cft |
Nineteen 50 kg bags contain 950 kg. That purchase quantity is slightly above the calculated mass because you cannot order a fraction of a sealed bag. The sand and crush figures have not been rounded to truck loads.
Three quotes, three units
Enter cement price per bag, sand price per cft and crush price per cft. The quote total uses whole cement bags but the calculated loose volumes for the other materials.
If only one quote is entered, the total includes only that priced component. Check all three rate fields before treating the result as a complete material budget. Water, additives, labour and delivery are outside it.
When this estimate is the wrong starting point
For ready mixed concrete, obtain the supplier’s price and specified performance for the required wet volume. Converting that order into a nominal site mix does not make it equivalent.
For site batching, moisture, aggregate grading and the required concrete performance need more information than these volume proportions provide. Keep the calculator as a quantity worksheet and leave mix approval to the relevant specification or qualified designer.
Save the CSV with the assumptions visible, especially if you change the bag size, density or dry factor. Otherwise a later reader may see the same volume and expect the default quantities.