Concrete
Concrete Slab Calculator
Estimate concrete volume, bags, material weight, mixer batches, and an optional bagged-versus-ready-mix cost check using only the prices and fees you enter.
Calculator inputs
Concrete Slab Calculator Results
Results update in your browser as you edit inputs. Use the shopping-list button for a printable project summary.
Enter project dimensions to calculate material quantity.
Assumptions
- The slab is treated as a simple rectangle with even thickness.
- Base material, forms, reinforcement, vapor barrier, and finishing materials are not included.
- Bag yield must come from the bag label or your supplier.
- Packaged weight uses the selected preset bag size or the custom bag weight you enter; it is not the cured slab weight.
- Mixer batches and time use only the capacity and minutes per batch you enter. Loading, cleanup, breaks, placement, and finishing time are not included.
- The ready-mix cost check uses only values you enter. It is not a supplier quote and does not include taxes or unentered charges.
- Check local building codes, permit requirements, product labels, and qualified professionals for structural or safety-critical work.
- Cost outputs use only the unit prices you enter.
Formula
- Volume in cubic feet = length x width x thickness in feet.
- Cubic yards = cubic feet divided by 27.
- Waste-adjusted volume = volume x (1 + waste factor).
- Bags = waste-adjusted cubic feet divided by selected bag yield, rounded up.
- Mixer batches = estimated bags divided by your entered bags per batch, rounded up.
- Ready-mix cost = the larger of required cubic yards or your entered minimum order, multiplied by your entered price per cubic yard, plus entered delivery and short-load fees.
How to Use the Concrete Slab Calculator
- Enter the slab length and width in feet.
- Enter thickness in inches, using the design or product requirement for your project.
- Choose the concrete bag yield from the product label.
- Add waste for uneven excavation, form variation, overdig, or small losses.
- Optionally enter your mixer capacity and pace to estimate batches and active mixing time.
- For a cost check, enter only bag or ready-mix prices, minimums, and fees you already have.
Concrete Slab Calculator Examples
10 ft x 10 ft slab at 4 in thick
A 10 ft by 10 ft slab at 4 in thick is about 33.33 cu ft, or 1.23 cu yd, before waste. With 5% waste, it is about 35.00 cu ft, or about 59 bags at 0.60 cu ft per bag.
- Area: 100 sq ft
- Thickness: 4 in
- With 5% waste: about 35.00 cu ft
- Bag count: about 59 at 0.60 cu ft/bag
12 ft x 12 ft shed slab at 4 in thick
A 12 ft by 12 ft slab at 4 in thick is about 48.00 cu ft before waste. With 5% waste, the estimate is about 50.40 cu ft, or 1.87 cu yd.
- Area: 144 sq ft
- Thickness: 4 in
- With 5% waste: about 50.40 cu ft
- Cubic yards: about 1.87
10 ft x 10 ft slab mixing plan
The 59-bag example becomes 30 mixer batches when you enter 2 bags per batch. At 5 minutes per batch, the active mixing-time estimate is 150 minutes before loading, placement, breaks, cleanup, and finishing.
- Estimated bags: 59
- Entered capacity: 2 bags per batch
- Mixer batches: 30
- Entered pace: 5 minutes per batch
Units and Parameters Quick Reference
Concrete slab inputs
Concrete volume is very sensitive to thickness. A one-inch thickness change can add several bags on small slabs.
| Input | Unit | Planning note |
|---|---|---|
| Slab length and width | ft | Use finished form dimensions. |
| Slab thickness | in | Confirm the required thickness before estimating bags. |
| Bag yield | cu ft/bag | Use the yield printed on the bag. |
| Waste factor | % | Adds extra concrete after base volume is calculated. |
| Bags per batch | bags | Use the capacity you actually run in your mixer. |
| Ready-mix values | your currency | Enter a supplier price, minimum, and fees only when you have them. |
This calculator does not include forms, rebar, mesh, gravel base, finishing tools, labor, or any supplier charge you do not enter.
Planning reference
10 x 10 slab thickness reference
This quick reference uses a 10 ft by 10 ft slab, 5% waste, and an 80 lb bag yield of 0.60 cubic feet.
| Thickness | Concrete with waste | 80 lb bags |
|---|---|---|
| 3 in | 26.25 cu ft / 0.97 cu yd | 44 bags |
| 4 in | 35.00 cu ft / 1.30 cu yd | 59 bags |
| 5 in | 43.75 cu ft / 1.62 cu yd | 73 bags |
| 6 in | 52.50 cu ft / 1.94 cu yd | 88 bags |
Do not use this table for structural design. Confirm slab thickness, base preparation, reinforcement, and permits separately.
What the concrete results mean
Cubic feet and cubic yards describe the waste-adjusted concrete volume. Estimated bags divide that volume by the selected bag yield and round up to a whole bag.
Total packaged weight helps with pickup and handling plans; it is not the cured slab weight. Mixer batches and active mixing time appear only when you enter your own batch capacity and pace.
Bagged concrete or ready mix?
The calculator presents both paths without choosing one for you. Bagged concrete uses the rounded bag count and your entered bag price. Ready mix uses the waste-adjusted cubic yards, your entered minimum order, and the supplier charges you enter.
Cost is only one part of the decision. Also check access, placement time, mixer capacity, crew size, supplier terms, and whether the pour can be completed without creating unwanted cold joints.
Example calculation
Example: 10 x 10 slab
A 10 ft by 10 ft slab at 4 in thick is about 33.33 cubic feet, or 1.23 cubic yards, before waste.
Common mistakes
- Entering slab thickness in feet instead of inches.
- Ignoring uneven excavation or overdig.
- Comparing bagged and ready-mix cost without adding the supplier minimum order and fees you were quoted.
- Treating estimated mixing minutes as total project time.
- Using volume output as a structural thickness, reinforcement, or disposal plan.
FAQ
Does this calculate ready-mix truck pricing?
It does not look up or supply ready-mix pricing. If you enter a price per cubic yard, minimum order, delivery fee, and short-load fee from a supplier, it totals those values for a planning comparison.
What bag yield should I enter?
Enter the cubic-foot yield printed on the concrete bag you plan to use.
Can this work as a concrete slab cost calculator?
Only as a user-entered material estimate. A bag price is multiplied by the rounded bag count. For ready mix, your entered cubic-yard price, minimum order, delivery fee, and short-load fee are totaled. It does not fetch local prices or include labor, taxes, permits, forms, reinforcement, or finishing work.
How much concrete do I need for a 10x10 slab?
At 4 inches thick, a 10x10 slab needs about 33.33 cu ft before waste. With 5% waste, that is about 35.00 cu ft, 1.30 cu yd, or 59 bags at 0.60 cu ft per bag.
How do I calculate concrete for an L-shaped or irregular slab?
Split the slab into simple rectangles, run each rectangle through the calculator at the same thickness, then add the cubic feet, cubic yards, and bag counts together. For a curved or rounded edge, use the smallest rectangle that fully contains the shape and rely on the waste factor, or estimate the area separately and treat it as one more rectangle of equal area.
How many 80 lb bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet, and an 80 lb bag yields about 0.60 cubic feet, so a cubic yard takes about 45 bags of 80 lb concrete (27 / 0.60). A 60 lb bag yields about 0.45 cubic feet, so it takes about 60 bags per cubic yard, and a 40 lb bag takes about 90. Confirm the exact yield on your product label.
Does a concrete slab need rebar?
It depends on the slab use, soil, and local code. Many patios and shed slabs use welded wire mesh or rebar to control cracking, while driveways and structural slabs usually require reinforcement sized by a professional. This calculator estimates concrete volume only and does not include rebar, mesh, or a reinforcement design. Confirm requirements with your local building department.
How do I choose bags per mixer batch?
Enter the number of bags you actually load for one batch. Use the mixer instructions and stay within its rated capacity; the calculator does not choose a safe batch size for you.
Does estimated mixing time include the whole pour?
No. It multiplies rounded mixer batches by the minutes per batch you enter. Loading, moving, placing, breaks, cleanup, and finishing are separate.
Sources and review notes
Reviewed . These references support the unit conversions and planning assumptions on this page. Confirm the exact product label and local project requirements before buying material.
- How the calculations work HomeMaterialCalc. How HomeMaterialCalc handles formulas, rounding, browser-based calculations, and prices you enter.
- NIST Guide to the SI, Appendix B: Conversion Factors National Institute of Standards and Technology. Length, area, and volume unit conversions used in calculator formulas.
- QUIKRETE Concrete Mix No. 1101 data sheet QUIKRETE. Planning yields for 40 lb, 60 lb, and 80 lb concrete bags.
Next planning steps
Continue with a related calculator, worked example, chart, or guide for the next part of your project.
Related Material Guides
Read these planning guides when you want more context for the assumptions, depth, thickness, waste factor, or bag-yield inputs used by this calculator.