Calculation
1Volume of one slab or footing pad
V_1 = L \times W \times t
V_1 = 6.000 \times 4.000 \times 0.150 = 3.600
V_1=3.600 m³
2Order volume including waste allowance
V_{order} = V_{net} \, (1 + w)
V_{order} = 3.600 \times (1 + 0.100) = 3.960
V_{order}=3.960 m³
Waste allowance 10%.
3Bags of mix
n_{bags} = \left\lceil \frac{V_{order}}{v_{bag}} \right\rceil
n_{bags} = \lceil 3.960 / 0.0170 \rceil = 234
n_{bags}=234
80 lb bags at a nominal 0.6 ft³ per bag.
Notes
- At 234 bags this pour is past the point where bagged mix is practical; ready-mix is usually cheaper and more consistent above roughly 1 m³.
Assumptions
- Dimensions are neat (out-to-out) with no deduction for reinforcement, embedded items or openings.
- The waste allowance covers spillage, over-excavation and formwork deflection; it is not a substitute for measuring.
What this calculator does not check
- Does not deduct openings, recesses, or embedded items.
- Does not compute reinforcement, formwork area, or mix proportions.
- Bag counts use a nominal yield per bag and will differ between manufacturers — check the bag.
- Ready-mix suppliers round up to the truck; the truck-load figure is an estimate, not an order quantity.
Results are for preliminary sizing and educational use. They are not a design and must be reviewed, verified and sealed by a licensed or registered engineer before being used in construction.
concrete-volume v1.0.0 · n/a · input 152c92d03fa39d4a