Total Volume
33.3ft³
≈ 1.23 yd³ · includes waste buffer.
Quick Start
Load from sample build
Start from a common concrete project, then edit the dimensions and material settings to match your exact job site.
Step 1
Project dimensions
Measure the inside of your forms for slabs, and the tube diameter and depth for holes. Round up on anything you are unsure about — leftover concrete is cheaper than a short pour.
Tubes (Sonotubes) are pre-formed, so no form boards needed.
ft
ft
in
in
Slabs are usually 4″. Footings and piers go deeper.
pcs
For post holes, enter the number of holes.
Denser grids resist cracking under heavier loads.
Step 2
Calculate concrete & supplies
Estimates update automatically as you type. Bag yields: 40 lb ≈ 0.45 ft³, 60 lb ≈ 0.67 ft³, 80 lb ≈ 0.90 ft³. Actual yields vary with mixing waste and subgrade depth.
Recommendation
Volume, bags & truck verdict
10×10 ft · 4″ slab40 lb Bags
74bags
≈ 0.45 ft³ per bag.
60 lb Bags
50bags
≈ 0.67 ft³ per bag.
80 lb Bags
38bags
≈ 0.90 ft³ per bag.
Forms & Rebar
40 lin ft of form boards
Rebar: 120 lin ft (16″ grid).
Truck Verdict & Pro Notes
Action Plan
Pour day schedule
forms first, cure slowConcrete waits for nobody once it is mixed. Build the forms the day before, have every tool within reach, and know your finishing plan before the first batch hits the forms.
Shopping List
Lumber yard & hardware store run
Concrete, base, forms, steel, and finishing tools, in yard order. Quantities match this job’s math.
Gear
Concrete Mixing & Finishing Essentials
Affiliate disclosure: As an Amazon Associate, Gadget Earth may earn from qualifying purchases. Product availability and prices change frequently. We link to broad product categories — always compare specifications and reviews yourself.
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Learn
The concrete finisher’s field guide
Why Adding “Just a Little More Water” Ruins Your Concrete
Every extra gallon of water you add to make the mix easier to spread is strength you are throwing away. The water-cement ratio is what controls strength, and a soupy mix shrinks as it dries, leaving a web of hairline cracks and a dusty surface that never hardens right. The mix should feel like thick oatmeal: it holds its shape on a shovel and slumps off slowly, not runs.
If the mix feels too stiff in the wheelbarrow, the fix is to keep mixing, not to add water. If it stays stiff, the mix is off and another bag or a splash measured by the bag instructions is the limit. Every DIY slab I have torn out that cracked in the first year had the same story: someone kept the hose running while mixing because it poured easier. It always costs more later.
The “Cold Joint” Nightmare: Why You Can’t Pour a Large Slab in Two Days
Concrete starts setting the moment water hits the mix, and in summer sun it sets up fast. A cold joint is the weak line where yesterday’s set concrete meets today’s wet pour, and it is a crack waiting for its first freeze. You cannot pour half a slab on Saturday and finish Sunday — the seam will telegraph and crack.
So plan the pour like a project: under about 1 cubic yard you can hand-mix in batches you can pour and screed within 20 minutes each. Between 1 and 2.5 yards, rent a portable mixer so the batches keep coming. Over 2.5 yards, order the ready-mix truck, because you cannot mix fast enough by hand to beat the set. If you are pouring the pad for a standby generator, size the generator first with our home generator size calculator, then pour the pad to the installer’s spec.
Rebar Chairs: Why Your Steel Must Float in the Middle of the Slab
Rebar only strengthens the slab when it sits in the middle of the thickness, where it bridges the tension side of the slab under load. Rebar lying on the dirt does nothing but rust, and rust expands to several times its volume, spalling the surface from the inside — the classic orange crack that runs along the bottom of a DIY slab.
Set the grid on chairs or dobies so the steel sits at mid-depth, and tie the intersections with tie wire so the grid does not float or shift during the pour. For deck piers, the steel is the pier’s backbone, so keep the cages centered in the tube. If this pour is holding up a deck, our deck board and joist estimator sizes the structure that sits on top of it.
Broom Finish vs. Trowel Finish: Which One Do You Actually Need?
The finish you choose is about slip resistance, not looks. Any outdoor surface that gets wet — patios, ramps, garage aprons — needs a broom finish, because a smooth troweled surface turns into an ice rink with morning dew. A steel trowel finish is for interior slabs and garage floors that stay dry, where you want a hard, smooth, dust-resistant surface.
Timing is the whole game for both. Wait until the bleed water has fully evaporated off the surface before you touch it with anything. Finishing while bleed water is still on top traps water under the surface and causes dusting and scaling. Broom in one direction with light, even pressure, and pull a straight line every pass. Start too soon and you drag the surface; start too late and the broom tears it.
How to Cure Concrete So It Doesn’t Crack in the Sun
Curing is not drying — it is the chemical reaction that gives concrete its strength, and it needs water to keep going. A slab that dries too fast in sun and wind stops curing early, and it shows as shrinkage cracks and a dusty surface that never hardens. The fix is simple and most DIYers skip it: keep the slab damp for 5 to 7 days.
Soak the slab with a hose after the surface sets, then cover it with plastic sheeting to hold the moisture in, and re-soak once a day in hot weather. If you cannot keep it covered, use a spray curing compound. The slab you keep damp for a week will be visibly harder and crack less than the one you leave to the sun — same mix, same day, different slab. And when you are landscaping around the new slab, our garden bed spacing calculator helps you plan beds that sit clear of the edges.
FAQ
Frequently asked questions
How many 80lb bags of concrete do I need for a 10x10 slab that is 4 inches thick?
A 10×10 slab at 4″ thick is about 33.3 cubic feet, or 1.23 cubic yards. Each 80 lb bag yields about 0.9 cubic feet, so you need roughly 38 bags, and about 41 bags with the standard 10% waste buffer. At that volume, renting a mixer or ordering a truck beats mixing by hand.
Is it cheaper to buy bags of concrete or order a ready-mix truck?
For small jobs under about 1 cubic yard, bags usually win even after you count labor. Around 1.5 to 2 cubic yards the cost is close, and the truck wins on labor. Over 2.5 yards the truck is the right call either way, because hand-mixing that much creates cold joints where wet concrete meets drying concrete. Get local quotes, because short-load fees change the math.
Do I need gravel under a concrete slab?
Yes, two to four inches of compacted gravel under a slab in almost every case. The gravel base drains water away so frost heave cannot lift the slab, keeps the concrete from mixing with mud, and gives the slab uniform support. Slabs poured on dirt crack and sink where the soil washes out or freezes.
How long does it take for concrete to fully cure?
Concrete reaches full design strength at about 28 days, but that does not mean you wait 28 days to touch it. You can walk on it after a day or two, keep it damp under plastic for the first 5 to 7 days, and keep cars off a slab for about a week. Curing is not drying; it is the chemical reaction that gives concrete its strength.
Can I pour concrete directly over dirt?
Not if you want the slab to last. Organic soil rots and compresses, so the slab settles and cracks where the support disappears. Strip the topsoil, compact the subgrade, add a compacted gravel base, and then pour. Pouring straight on dirt is the most common reason DIY slabs crack in the first winter.
What is the difference between cement and concrete?
Cement is one ingredient; concrete is the finished product. Portland cement is the gray powder that reacts with water and hardens. Concrete is cement mixed with sand, gravel, and water. Buying a bag of pure cement and expecting concrete is like buying flour and expecting bread; the aggregate is most of the strength.
How do I keep my wooden forms from sticking to the concrete?
Coat the inside faces of the forms with form release oil before the pour; vegetable oil works in a pinch. Dry wood drinks water out of the concrete and bonds to it, and prying un-oiled forms off tears chunks out of the edges. Screw the forms from the outside so you can unscrew instead of pry.
How deep do I need to dig post holes to prevent frost heave?
Below your local frost line, which runs from about 12 inches in warm climates to 48 inches or more in cold ones. Frozen ground expands and lifts anything set above the frost line, then the post never settles back. Your local building department publishes the required depth, and it is the first thing an inspector checks. If the hole is holding a fence post, our fence post and panel estimator counts the posts and panels for the run.
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