Measurement & Materials
Concrete slab volume and bags
Calculate concrete for rectangular slabs from dimensions or known area, depth, an allowance and the actual mix bag yield.
Your inputs
Complete the fields for your selected method. Zero means intentionally zero, not unknown. Currency selection labels amounts; it does not convert exchange rates.
How this calculation works
net cubic feet = net square feet × thickness in inches / 12; cubic yards = cubic feet / 27; bags = ceil(order cubic feet / yield per bag)
A quantity estimate from your measurements, not a drawing takeoff, layout optimization, engineering design or code approval. Keep overlapping sections out of the total. Material allowances are your assumptions; supplier package sizes, product coverage and prices must come from the actual product or quote. Optional prices entered as zero are omitted; cost subtotals include only entered prices. Thickness must be supplied from your project requirements; this tool does not select slab thickness, strength or reinforcement. Uniform thickness is assumed. Allow separately for uneven substrate and supplier ordering increments.
What information do I need?
Use records for the same job, equipment or accounting period. Only the fields for your selected entry method are required. An unknown amount is not zero.
Input definitions and where to find them
- Which area information do you have?: Use matching records or an explicitly identified assumption for which area information do you have?. Unknown is not the same as zero.
- Rectangular sections — add each nonoverlapping section once: Use matching records or an explicitly identified assumption for rectangular sections — add each nonoverlapping section once. Unknown is not the same as zero. Used with: Measure rectangular sections.
- Section name: Use matching records or an explicitly identified assumption for section name. Unknown is not the same as zero.
- Section length (ft): Measure this distance. Choose feet, inches or meters beside the field; decimal feet and decimal inches are accepted. Use the feet-and-inches tool to convert fractions if needed.
- Section width (ft): Measure this distance. Choose feet, inches or meters beside the field; decimal feet and decimal inches are accepted. Use the feet-and-inches tool to convert fractions if needed.
- Already measured area (ft²): Enter the measured surface area in the selected unit, not a length. Use net area after deductions only if those deductions will not be entered again. Used with: I already know the area.
- Openings or uncovered area to subtract (ft²): Enter the measured surface area in the selected unit, not a length. Use net area after deductions only if those deductions will not be entered again.
- Slab thickness (in): Measure this distance. Choose feet, inches or meters beside the field; decimal feet and decimal inches are accepted. Use the feet-and-inches tool to convert fractions if needed.
- Extra volume allowance (%): Use matching records or an explicitly identified assumption for extra volume allowance. Unknown is not the same as zero.
- Concrete yield per bag from the product label (ft³/bag): Use matching records or an explicitly identified assumption for concrete yield per bag from the product label. Unknown is not the same as zero.
- Optional price per bag (0 to omit) (selected currency): Use matching records or an explicitly identified assumption for optional price per bag (0 to omit). Unknown is not the same as zero.
- Optional delivered concrete price per cubic yard (0 to omit) (selected currency): Use matching records or an explicitly identified assumption for optional delivered concrete price per cubic yard (0 to omit). Unknown is not the same as zero.
Use the Where to find this value controls beside the inputs for available work-it-out helpers. Estimates remain your assumptions; a helper does not verify the source figures.
Worked example
Example amounts use US dollars (USD).
Example answer: Net concrete volume is 1.4815 yd³ for the illustrative inputs below.
Example inputs
- Which area information do you have?: Measure rectangular sections
- Rectangular sections — add each nonoverlapping section once
- Section name: Section 1
- Section length: 12.00 ft
- Section width: 10.00 ft
- Openings or uncovered area to subtract: 0.00 ft²
- Slab thickness: 4.00 in
- Extra volume allowance: 5.00 %
- Concrete yield per bag from the product label: 0.60 ft³/bag
- Optional price per bag (0 to omit): $0.00
- Optional delivered concrete price per cubic yard (0 to omit): $0.00
- Net concrete volume
- 1.4815 yd³
- Order volume including allowance
- 1.5556 yd³
- Order volume in cubic feet
- 42.0000 ft³
- Whole bags at supplied yield
- 70 bags
- Bagged concrete material cost
- No price entered
- Bulk concrete volume cost
- No price entered
- Bag and bulk costs are alternative purchasing comparisons, not costs to add together. Bulk minimums, delivery, short-load charges, reinforcement, labor and tax are excluded.
These illustrative values are not recommended rates or industry averages. Replace every example input with your own figures.
Use the result well
Use the net measured quantity to check a material order or quote. Keep installed area, extra material and purchased quantities separate.
Keep inputs on the same scope and time basis. Calculations retain precision internally; displayed values generally round to two decimal places, with extra precision for very small values and whole-unit rounding where required. Economic comparisons describe your supplied assumptions and do not guarantee future results.
This tool provides business arithmetic. It does not approve engineering designs, establish legal or tax treatment, select equipment or certify safe operating conditions.