Calculator inputs
The page stays in a single-column flow, while the calculator fields use a responsive three-column, two-column, and one-column layout.
Plotly graph
This chart compares the slab’s wet volume, adjusted order volume, and dry material estimate in cubic meters.
Example data table
| Length | Width | Thickness | Waste | Wet Volume | Order Volume | Approx. yd³ |
|---|---|---|---|---|---|---|
| 10 ft | 8 ft | 4 in | 5% | 0.755 m³ | 0.793 m³ | 1.037 yd³ |
| 12 ft | 10 ft | 4 in | 5% | 1.133 m³ | 1.190 m³ | 1.557 yd³ |
| 6 m | 4 m | 0.15 m | 8% | 3.600 m³ | 3.888 m³ | 5.086 yd³ |
| 20 ft | 16 ft | 5 in | 7% | 3.776 m³ | 4.040 m³ | 5.284 yd³ |
Formula used
1. Slab area
Area = Length × Width
2. Wet concrete volume
Wet Volume = Length × Width × Thickness
3. Adjusted order volume
Order Volume = Wet Volume × (1 + Waste% / 100)
4. Dry material estimate
Dry Estimate = Order Volume × Dry Factor
5. Concrete weight
Weight = Order Volume × Density
6. Bag estimate
Bags = Concrete Weight ÷ Bag Weight
7. Cost estimate
Cost = Order Volume in Price Unit × Unit Price
The calculator converts all dimensions into meters first. Then it computes geometry, waste allowance, unit conversions, weight, bag count, truck planning, and cost.
How to use this calculator
- Enter slab length and width, then choose the unit for those plan dimensions.
- Enter slab thickness and select its thickness unit separately.
- Set waste percentage, density, bag size, price basis, truck capacity, and dry factor.
- Choose your preferred primary output unit for the headline result.
- Press Calculate slab volume to show the result above the form, then export the result as CSV or PDF.
Frequently asked questions
1. What formula does this slab calculator use?
It multiplies length, width, and thickness to get wet volume. Then it adds waste, converts units, estimates concrete weight, and calculates bag count, truck loads, and cost.
2. Why should I add a waste percentage?
Waste covers spillage, uneven base conditions, over-excavation, and finishing losses. Adding 5% to 10% helps avoid running short during the pour.
3. Should I order the wet volume or adjusted volume?
Use wet volume for geometric checking. Use adjusted order volume when buying concrete because site conditions and handling losses rarely stay perfect.
4. Can I use feet for plan size and inches for thickness?
Yes. Length and width use one unit selector, while thickness has its own selector. That makes common slab entry much easier.
5. How is the bag estimate calculated?
The calculator finds concrete weight from order volume and density, then divides that weight by your bag size. It gives an approximate premix bag count.
6. Does density affect the result?
Yes. Volume stays the same, but total weight and bag count change. Normal concrete often uses about 2,400 kg/m³, while specialty mixes can differ.
7. Why are truck loads rounded up?
Concrete deliveries must be planned as practical loads. Rounding up helps prevent shortages, especially when access, pumping, or finishing delays increase waste.
8. Can I use this for reinforced slabs?
Yes for concrete quantity planning. Reinforcement changes structural design, not slab geometry. Structural checks for steel, joints, thickness, and subbase should still be done separately.