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Concrete Slab Curb Stair and Column Budget

Estimate concrete volume, mass, bag equivalents and cost for slabs, curbs, solid stairs or columns.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A 4 m by 2 m slab at 10 cm thickness contains 0.8 m³. At 2000 kg/m³ and 10% waste, that is 70.4 mass-equivalent 25 kg bags. The unrounded equivalent budget at 5 per bag is 352.

Concrete mass = volume×density; equivalent bags = mass×(1+waste fraction)/bag mass; slab volume = length×width×thickness×count.

Worked example

Enter these known values and leave the other values blank.

Length
4 m
Width
2 m
Height/depth
10 cm
Quantity
1 pieces
Density
2000 kg/m³
Bag size
25 kg
Waste
10 %
Cost per bag
5 USD /bag
Total area
8 m²
Volume
0.8 m³
Weight
1600 kg
Equivalent concrete bags
70
Cost per slab
352 USD /piece
Cost per unit area
44 USD / m²
Cost per unit volume
440 USD / m³
Equivalent bag material budget
352 USD

Assumptions and limitations

  • Bag counts are continuous mass equivalents; buy the next whole bag count and verify product yield. Stair volume models solid stacked steps, not an open sloping carriage. Shapes exclude reinforcement displacement, form losses and site-specific foundation or strength requirements. The bag-based budget prorates the unrounded equivalent bag count; whole-bag purchase cost can be higher.
  • Use compatible measurement units. Clear an unknown before solving for it, and lock independent known values when comparing changes. Currency choices label amounts without exchange-rate conversion.

Common questions

Can I solve backward from the result?

Clear the unknown and enter independent known values. A rounded whole count cannot uniquely recover a continuous dimension; keep the original measured dimensions for procurement planning.

How many whole bags should I purchase?

Round the calculated mass-equivalent count upward to a whole bag and check the product yield. The mix-ratio options are volume arithmetic and do not certify concrete performance.

References

Enforce the stated physical geometry and whole-count domains. Integer membership is checked with isInteger, so ordinary, tiny and large fractional counts are rejected even when tolerant floor equality would pass. Bookify replaces the captured rounded US gallon with the exact 3.785411784-liter definition. Bookify uses exact customary mass and volume definitions for density units, replacing rounded factors in the reference.

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