Concrete Slab Calculator
Concrete volume, bag quantities and material cost from slab dimensions.
Project inputs
Examples
Supplier prices (optional)
Prices exclude delivery, tax and labor. Currency changes labels only.
Estimate
Start with your measurements.
Your order quantity, purchasing options and material cost appear here.
Overage is included in purchasing quantities. Check product yields before ordering.
Check product yields and project specifications. Material subtotals exclude delivery, tax, labor and equipment. These quantities do not specify structural dimensions or reinforcement.
Estimate
Confirm supplier order increments.
Prices shown in your local currency ($)
Ordering notes
Compare bags and ready-mix
| Factor | Bags | Ready-Mix |
|---|---|---|
| Estimated Cost | — | — |
| Practicality | — | — |
| Volume reference | Pours under 1 cu yd | Pours over 1 cu yd |
| Ordering check | — | — |
Worked example
10 × 10 ft slab, 4-inch depth and 10% overage.
- Step 1; Volume 10 × 10 × (4 ÷ 12) ft = 33.33 cu ft
- Step 2; Cubic Yards 33.33 ÷ 27 = 1.23 cu yd
- Step 3; Add 10% Waste 33.33 × 1.10 = 36.67 cu ft
- Step 4; 60 lb Bags 36.67 ÷ 0.45 = 82 bags
- Step 5; 80 lb Bags 36.67 ÷ 0.60 = 62 bags
- Recommendation At 1.23 cu yd, this sits right at the crossover; ready-mix saves time, bags work for a patient DIYer.
Calculation method
Volume formula: Volume = Length × Width × Thickness. It converts that volume into cubic yards (for ready-mix orders) and into bag counts for both 60 lb and 80 lb bags.
Each 60 lb bag of concrete mix yields approximately 0.45 cubic feet. Each 80 lb bag yields about 0.60 cubic feet. The calculator applies your chosen waste factor and multiplies by your local prices to give you a total cost estimate for each option.
Ordering: Compare the effort of mixing the bag quantity with a supplier quote for delivery. Ready-mix minimums, order increments and fees vary.
Project notes
- Check the specification. Use the project’s thickness and base requirements; this calculator estimates the dimensions you enter.
- Water-to-cement ratio: Don't add extra water to make mixing easier; it weakens the concrete significantly.
- Curing: Follow the selected mix and project instructions for moisture, temperature and loading times.
- Ordering increments: Confirm the supplier’s bag yields, delivery minimums and order increments.
Input and ordering checks
Forgetting depth. People calculate length × width but forget the thickness. A 10×10 slab looks small until you realize 4 inches deep means over 1 cubic yard.
Unit confusion. Mixing feet and inches without converting. Convert thickness to feet before calculating (4 inches = 0.333 ft). This calculator handles it automatically.
Skipping the waste factor. Allow for uneven ground, spillage and over-excavation. 10% is a starting allowance; confirm the overage with your supplier.
Buying bags for a large pour. Over 1 cubic yard, ready-mix can reduce mixing effort; compare supplier quotes, delivery fees, and mix specifications.
Assumptions
QUIKRETE Concrete Mix technical data provides the 0.45 ft³ and 0.60 ft³ bag yields used here. Other mixes can have different yields.
- ◦ Concrete yield: 60 lb bags = 0.45 cu ft; 80 lb bags = 0.60 cu ft. These are approximate yields for QUIKRETE Concrete Mix No. 1101; confirm the selected product label.
- ◦ Waste factor: The default 10% accounts for spillage, uneven subgrade, and slight over-excavation. Increase to 15% for rough terrain or irregular shapes.
- ◦ Prices vary by region: Ready-mix costs vary by region and supplier. Bag prices vary by brand. Update the inputs to reflect your local prices for material subtotals.
- ◦ Ready-mix delivery fees: Delivery fees, minimum orders and order increments vary by supplier. Factor these into your cost before comparing options.
- ◦ Results are estimates only: This tool is a planning aid. Confirm quantities with your concrete supplier or contractor before ordering materials.