Concrete Slab & Bag Quantity

When to use it

For planning bags of pre-mixed concrete for identical rectangular slabs. Enter dimensions from an existing design and the actual finished yield stated for the product. Save your bag size, allowance and quoted price with the project.

Inputs

USD

Calculation method

Multiply length, width, thickness and slab count. Apply your allowance once, divide by finished yield per bag, and round upward. Multiply whole bags by yield for purchased volume and by bag price for cost. The example 10 × 6 ft at 4 in gives 20 ft³; a chosen 5% allowance gives 21 ft³. At an entered yield of 0.60 ft³ per bag, buy 35 bags. A simulated USD 8 per bag totals USD 280.

10 [Internal slab length ft] × 6 [Internal slab width ft] × 4 [Thickness from your project design in] × 1 [Number of identical rectangular slabs] → Geometric volume of all slabs ft³

Geometric volume of all slabs ft³ × (1 + 5 [Additional purchase allowance]%) → Volume including your allowance ft³

ceil(Volume including your allowance ft³/0.6 [Finished concrete volume yielded by one bag ft³]) → Whole bags required, rounded upward

Whole bags required, rounded upward × Finished concrete volume yielded by one bag ft³ → Finished volume those bags would yield ft³

Finished volume those bags would yield ft³-Volume including your allowance ft³ → Purchased yield above the planned volume ft³

Whole bags required, rounded upward × 8 [Price of one bag USD] → Budget for concrete bags USD

Change one input

Change only thickness from 4 to 5 in. Planned volume becomes 26.25 ft³ and bags rise from 35 to 44. Yield purchased is 26.4 ft³, leaving 0.15 ft³ above plan; the material budget becomes USD 352.

Results are displayed to at most two decimal places; later formulas use unrounded values.

Scope and limits

• Bag yield is finished volume, not dry weight.
• Thickness comes from your project design.
• Prices and allowance are example inputs.

All dimensions and bag yield must be positive; slab count is a positive integer; allowance and price are nonnegative. Use the unrounded volume for whole-bag rounding. Product yields are approximate, so verify the current product sheet and your site conditions. The 0.60 ft³ input is based on one QUIKRETE 80 lb product example, not every concrete bag; the price is simulated. No aggregate mix recipe, reinforcement, structural design, labour, delivery or tax is included.

Product yield and whole-bag estimation: QUIKRETE.

Download and import into Calvance to edit the numbers. The canvas does not reject every invalid input; check the stated ranges.

Common questions

Can I enter the bag weight as its yield?

No. Use the finished volume stated by the manufacturer; pounds or kilograms do not by themselves determine that volume.

Is the extra yield another waste allowance?

No. It is the difference caused by buying whole bags after the chosen allowance has already been applied.

How to import your template

We recommend using the latest version of Calvance.

1. Save the file. Choose Download template and save the .calvx file to Files on your iPhone or iPad. From a computer, you can send it to your device with AirDrop.
2. Open Import. In All Canvases in Calvance, tap the add button to open the template screen, then choose Import.
3. Choose the file. Select the saved .calvx file to create your own canvas. Importing uses one canvas from your allowance.
4. Edit and check. Check the results against the worked example, then add your numbers. Duplicate the canvas to keep different versions.

Download .calvx file