Concrete Calculator
Ready-mix is ~$120-$150/yd3 delivered. One 80 lb bag = 0.6 cu ft.
Recommended: 5-10%. Form leakage, subgrade irregularities, and spillage from truck or mixer.
Concrete Calculator: How Much Concrete Do You Need?
Ordering concrete is unforgiving — a short pour can ruin a slab, and excess ready-mix gets expensive fast once it's in the truck. Our free concrete calculator takes your slab, footing, or patio dimensions and instantly tells you how many cubic yards you'll need, plus the equivalent number of 80 lb bags if you're mixing by hand. It also estimates labor, sales tax, and delivery so you have a full project cost before you order.
How the Concrete Calculator Works
Concrete volume depends on the length, width, and thickness of your pour. Patios and sidewalks are typically 4 inches thick, while driveways handling vehicle loads often go 4 to 6 inches. Our calculator converts your dimensions into cubic yards and cubic feet, then multiplies by your local ready-mix price or bag price to build a complete cost estimate — including labor time, sales tax, and delivery fees.
Why This Calculator Has an Adjustable Waste Buffer
This calculator applies the adjustable waste buffer on top of your raw calculated volume. Concrete work involves form leakage, over-excavation, uneven sub-grade, and spillage during placement and finishing — this buffer accounts for that, so you don't end up short mid-pour with concrete already curing in the truck.
If your forms are precise and your site is well-prepped, you can adjust the waste buffer percentage directly on this calculator — set it anywhere from 0% to 50% to match your comfort level. Lowering it will reduce both the material estimate and the total cost shown. Because concrete can't be "topped off" once a truck leaves, most contractors prefer to round up rather than down.
Concrete Slab Thickness Guide
| Project | Recommended Thickness | Notes |
|---|---|---|
| Patio / walkway | 4 inches | Standard for foot traffic only |
| Residential driveway | 4–6 inches | Thicker for heavier vehicles |
| Garage floor | 4–6 inches | Often reinforced with rebar or mesh |
| Footings | Per local code | Depth depends on frost line and load |
Ready-Mix vs. Bagged Concrete
One cubic yard of concrete requires roughly 45 bags of 80 lb concrete mix. For small pours — footings, fence post holes, small pads — bagged concrete mixed by hand or with a mixer is usually more practical. For anything over a cubic yard or two, ordering ready-mix delivered by truck is almost always faster and cheaper per unit.
Frequently Asked Questions
How much concrete do I need for a 10x10 slab?
At a standard 4-inch thickness, a 10x10 ft slab needs about 1.23 cubic yards of concrete. With a 10% waste buffer applied, that comes out to roughly 1.36 cubic yards, or about 62 bags of 80 lb mix.
How many 80 lb bags are in a cubic yard of concrete?
One cubic yard requires approximately 45 bags of 80 lb concrete mix, since each bag yields about 0.6 cubic feet of mixed concrete.
How thick should a concrete slab be?
Most patios and walkways use a 4-inch slab. Driveways and garage floors are commonly 4 to 6 inches, with thicker pours for heavier vehicles or equipment.
What is a good waste buffer for concrete?
5-10% is a practical range for most pours. Precise, well-formed slabs can stay near 5%, while irregular shapes, sloped sites, or hand-mixed pours often belong closer to 10%.
How long does concrete take to cure?
Concrete hardens within a few hours but continues curing for about 28 days. Light foot traffic is often fine after 24 to 48 hours, while vehicle traffic usually needs at least 7 days.
What's the difference between concrete and cement?
Cement is one ingredient in concrete. Concrete is the mixture of cement, sand, gravel, and water that hardens into the finished material.
Related Calculators
Planning a full landscaping project? These calculators pair well with concrete:
Deck Calculator — estimate materials for a deck built alongside a concrete patio or footing.
Retaining Wall Calculator — plan block and base gravel for walls that use concrete footings.
Fence Calculator — figure out post and concrete footing needs for a new fence line.