Calculator Inputs
Example Data Table
| Wet Volume | Unit | Mix Ratio | Bag Size | Wastage | Recommended Bags | Sand (dry) | Aggregate (dry) |
|---|---|---|---|---|---|---|---|
| 1.000 | m³ | 1:2:4 | 50 kg | 5% | 7 bags | 0.514 m³ | 1.028 m³ |
| 3.000 | yd³ | 1:1.5:3 | 40 kg | 8% | 66 bags | 4.052 yd³ | 8.104 yd³ |
| 750.000 | L | 1:3:6 | 50 kg | 3% | 3 bags | 0.531 m³ | 1.061 m³ |
Formula Used
- Dry volume: Dry = Wet × Dry Factor
- Component volume: Component = Dry × (Part ÷ Total Parts)
- Cement weight: Cement kg = Cement volume × Cement density
- Raw bags: Bags = Cement kg ÷ Bag size
- With wastage: Bagsw = Bags × (1 + Wastage/100)
- Final bags: Apply rounding (Up / Nearest / Down)
- Water estimate (optional): Water L = (w/c) × Cement kg
How to Use This Calculator
- Enter your concrete volume from plans or site measurements.
- Select the unit used on your drawings for consistency.
- Choose a mix ratio based on the required strength class.
- Set bag size and wastage to match procurement reality.
- Press calculate to view bags, sand, and aggregate totals.
- Export CSV or PDF to share with purchasing or crews.
Volume to Materials Conversion
The calculator starts with wet concrete volume from drawings, takeoffs, or measured forms. It converts the chosen unit to cubic meters, then applies a dry volume factor to reflect batching losses, voids, and bulking in loose ingredients. Typical planning factors range from 1.52 to 1.57, but you can adjust for local practice or project specifications. This step prevents under-ordering when materials are measured by bags and stockpiles.
Mix Ratio Allocation
After dry volume is calculated, the mix ratio (cement:sand:aggregate) splits total parts into fractions. Cement, sand, and aggregate volumes are computed as Dry × (Part ÷ Total Parts). Common ratios include 1:2:4 for general work and 1:1.5:3 for higher strength mixes. Sand and aggregate are returned in your selected unit to align with loader buckets, delivery tickets, and storage bins.
Cement Weight and Bag Count
Cement volume is converted to kilograms using a configurable density value, with 1440 kg/m³ as a used default. The result is divided by bag size (50, 40, 25, or 20 kg) to produce raw bag demand. A wastage percentage is applied to the bag count to cover spillage, torn packaging, partial mixing, and site handling. Choose rounding up for most pours to reduce the risk of stoppage from material shortfall.
Water Planning Output
An optional water estimate uses the water-cement ratio multiplied by cement weight. This supports planning for water tanks and batching, but it is not a final mix design. Moisture in sand, admixtures, target slump, and temperature can change actual water needs significantly. Always follow supplier guidance and site tests.
Practical Use in Construction
Use the recommended bags as your minimum cement order and validate against project specifications and strength requirements. Stage sand and aggregate volumes on site, then export CSV for costing and reconciliation, and PDF for field packets and approvals. Recheck inputs when geometry changes, waste risk increases, or a different bag size is supplied. For large pours, consider splitting calculations by pour segment to control deliveries.
FAQs
1) Why is a dry volume factor needed?
Wet concrete volume differs from loose ingredient volume. The factor covers bulking and voids so the bag count and aggregates are not underestimated during procurement.
2) Which rounding option is best?
Round up for most pours to avoid stoppage. Use nearest rounding for small work with fast resupply. Avoid rounding down unless you have verified surplus cement on site.
3) Do sand and aggregate include wastage?
The wastage setting is applied to cement bags only. If you want the same buffer for sand and aggregate, add a percentage buffer in ordering or slightly increase the input volume.
4) What density should I use?
1440 kg/m³ is a common planning value for cement. If your supplier provides a different bulk density or you have lab data, update the density to better match local materials.
5) Is the water output a final mix design?
No. It uses a simple water-cement ratio estimate. Real water demand depends on sand moisture, admixtures, temperature, and required slump, so follow specification and field testing.
6) Can I use other units like liters or cubic yards?
Yes. Select the unit that matches your documentation. The calculator converts internally and returns sand and aggregate in the same unit you selected for consistent site handling.