Concrete Calculator
From your first measurement to your final order. Calculate volume, add extra and price your pour.
The math behind your materials
How to calculate concrete
Measure each rectangular section separately. Convert all dimensions to the same unit, multiply them, then add the section volumes together.
In feet: volume ÷ 27 = cubic yards
In meters: volume = cubic meters
Multiply the total by 1 + (extra percentage ÷ 100). Only then round up to whole bags or the supplier’s ordering increment. A minimum ready-mix order is applied before increment rounding.
A 12 × 16 ft patio, 4 in thick
12 × 16 × (4 ÷ 12) = 64 ft³, or about 2.3704 yd³. With 10% extra, that’s 70.4 ft³ (about 2.6074 yd³). An order increment of 0.25 yd³ gives a purchase quantity of 2.75 yd³.
If your chosen bag yields 0.6 ft³, divide 70.4 by 0.6 and round up: 118 bags. Verify the yield on your specific product.
Before you order
How much extra concrete should I allow?
The 10% example is adjustable. Uneven subgrade, spillage and measurement differences can affect your requirement. Set an allowance that fits your project and confirm your order with the supplier.
Should I choose ready-mix or bags?
You can calculate both using the same measurements. Enter the delivered ready-mix price or the bag price to compare concrete costs. Equipment, labor, working time and supplier minimums also affect the choice.
How many bags are in one cubic yard?
One cubic yard is 27 cubic feet. Divide 27 by your product’s mixed yield in cubic feet per bag. For an illustrative 0.6 ft³ yield, that is 45 bags before extra allowance. A different product yield changes the count.
Does this choose a safe slab thickness?
No. The calculator measures volume for the dimensions you enter. It does not design a slab or specify reinforcement, concrete strength or foundation requirements. Use the thickness specified for your project.
What’s included in the cost?
The rounded concrete purchase quantity multiplied by your price, plus entered tax and delivery. Base materials, reinforcement, forms, labor, equipment and other supplier charges are excluded.
Real-world project example
How many bags of concrete for a 10 × 10 ft slab?
A 10 × 10 ft slab at 4 inches thick contains 33.33 cubic feet of concrete, or about 1.23 cubic yards, before extra allowance. With 10% added, plan for about 36.67 cubic feet (1.36 cubic yards). A common 80 lb concrete bag yields roughly 0.60 cubic feet, but check the actual package: at 0.60 cubic feet per bag, this example requires 62 whole bags after rounding up.
Before you buy materials
Concrete bag yield changes by product. Thickness, reinforcement, subbase, local code and delivery minimums must be checked for your project. For a ready-mix order, use the supplier’s actual increments and their advice on extra allowance.
Adjust the measurements, waste allowance and purchase options in the calculator above to estimate your own project; examples are for planning only.