Pour 1
Advanced options
Allow 5–10%, or 15% for holes bored in sand.
Used for the bagged-concrete comparison.
Supply only. Excludes pump and short-load fees.
This concrete calculator works out how much concrete you need for a slab, footing, post hole or set of steps — in cubic yards, bags, tons and delivered cost. Add as many pours as you like and it totals them into a single order.
The short answer
Concrete volume is length × width × thickness, all in feet, then divided by 27 for cubic yards. A 12 × 10 ft slab at 4 inches is 12 × 10 × 0.333 ÷ 27 = 1.48 yd³. Add 10% waste and order 1.75 yd³.
Quick version: at 4 inches thick, one cubic yard covers 81 square feet. Divide your area by 81 and you have the yardage in your head.
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How to use this concrete calculator
Pick what you’re pouring, enter three measurements, and the concrete calculator returns cubic yards along with the bagged equivalent, weight, truck loads and supply cost. Four shapes cover nearly every residential pour:
- Slab — garage pads, shed floors, patios, walkways, driveways
- Footing — strip footings and trenches, measured as a total run
- Post holes — fence posts, deck footings, mailbox and sign posts
- Steps — poured steps, where each tread carries the treads above it
Pouring several things the same day? Use Add another pour and the calculator totals every section into one order figure — which is what you want, since a single 3 yard delivery is far cheaper than three small ones.
Waste percentage, bag size and your local ready-mix rate sit behind Advanced options. Working in metric? Switch the header toggle to m / mm and results show cubic yards, cubic feet and cubic metres together.
The concrete calculator formula
Every concrete quantity is area times depth, then converted to cubic yards. The step people miss is converting thickness from inches to feet before multiplying. Multiply 12 × 10 × 4 and you get 480 — a meaningless number. Divide the inches by 12 first and you get the 1.33 cubic yards you actually need.
Cubic yards = Length (ft) × Width (ft) × (Thickness in ÷ 12) ÷ 27
3 in = 0.25 ft · 4 in = 0.333 ft · 5 in = 0.417 ft · 6 in = 0.5 ft · 8 in = 0.667 ft
Worked example — 12 × 10 ft patio at 4 inches
Batch plants sell in quarter-yard increments, so round up to the next quarter rather than the next whole yard.
Using the concrete calculator for footings, post holes and steps
Slabs are the easy case. These three come up constantly on a residential site and each uses a different formula.
Footings and trenches
A footing is a long, narrow slab. Measure the total run including returns around corners, then multiply by width and depth. Measure the trench you actually dug, not the one on the plan — excavators overcut, and a 16 inch trench that came out at 19 inches is 19% more concrete than you budgeted.
Cubic yards = Total run (ft) × Width (ft) × Depth (ft) ÷ 27
40 ft run × 16 in wide × 12 in deep
= 40 × 1.333 × 1 = 53.3 ft³
= 1.98 yd³
Footings for anything structural must extend below your local frost depth — zero in parts of the south, 48 inches or more across the northern states and Canada. Your building department publishes the figure, and it changes your concrete volume dramatically. A footing at 48 inches deep needs four times the concrete of the same footing at 12 inches.
Post holes and piers
Round holes use the circle formula. The mistake here is entering diameter where the formula wants radius, which returns four times too much concrete. The concrete calculator asks for diameter and halves it for you.
Cubic feet = π × (Diameter ft ÷ 2)² × Depth (ft) × Number of holes
12 in ⌀ × 30 in deep
= 3.1416 × 0.5² × 2.5
= 1.96 ft³ per hole — about 3.3 × 80 lb bags
Subtract the post itself if it’s a solid 4 × 4 or 6 × 6 in a tight hole. A 4 × 4 in a 12 inch hole displaces roughly 8% of the volume — small enough that it usually just becomes part of your waste allowance.
Poured steps
Steps are a stack of rectangular prisms, each one carrying the treads above it. The bottom step is the full height of the flight; the top step is one riser deep. The calculator handles this automatically, but by hand you work each step separately and add them.
Worked example — 4 steps, 4 ft wide, 7 in rise, 11 in tread
How much waste should you allow?
Waste is not optional and not the same on every job. Running short mid-pour is the worst outcome on a concrete site — you get a cold joint where the first placement stiffened before the next arrived, and that joint is a permanent weak line. Ordering a quarter yard too much costs about $40. Ordering a quarter yard too little can cost you the slab.
| Situation | Allow | Why |
|---|---|---|
| Slab on a formed, compacted base | 5% | Base is level, losses are minimal |
| Slab on a rough or ungraded base | 10% | Low spots swallow more than you expect |
| Footings in clay | 10–15% | Trench walls slump and overcut |
| Post holes bored in sand | 15% | Sides belly out below grade where you can’t see |
| Any pumped pour | +0.25 yd³ | Concrete left in the line never reaches the pour |
How much does a cubic yard of concrete cover?
This is the fastest way to sanity-check any concrete calculator result. One cubic yard is 27 cubic feet, so coverage is just 27 divided by the thickness in feet.
| Thickness | Coverage per yd³ | yd³ per 100 ft² |
|---|---|---|
| 2 inches | 162 ft² | 0.62 |
| 3 inches | 108 ft² | 0.93 |
| 4 inches | 81 ft² | 1.24 |
| 5 inches | 65 ft² | 1.54 |
| 6 inches | 54 ft² | 1.85 |
| 8 inches | 41 ft² | 2.47 |
Bags or ready-mix? Where the line sits
Under 0.5 yd³
Use bags
About 23 × 80 lb bags or fewer. Suppliers charge a short-load fee of $60–$150 that erases any per-yard saving.
0.5 – 1.2 yd³
Call around
23–54 bags is a serious day of mixing. Trailer-mix rental or a short-load delivery often wins once you value your own time.
Over 1.2 yd³
Order ready-mix
Bagged runs roughly three times the price per yard, and hand-mixing that much means your first batch sets before your last is placed.
Ready-mix supply: roughly $130–$180 per cubic yard across most US markets, before pump hire, short-load fees or weekend surcharges.
Bagged concrete: roughly $270–$400 per cubic yard once you count the 45 × 80 lb bags it takes to make one. Prices vary by region and by distance from the batch plant — get a quote for your ZIP code.
How thick should the pour be?
Thickness drives volume more than anything else, so settle it before you calculate. These are common US residential figures — anything structural should follow your local building code.
| Application | Thickness | yd³ per 100 ft² |
|---|---|---|
| Walkway, garden path | 3–4 in | 0.93–1.24 |
| Patio | 4 in | 1.24 |
| Shed floor | 4 in | 1.24 |
| Garage slab | 4–5 in | 1.24–1.54 |
| Residential driveway | 4–5 in | 1.24–1.54 |
| RV pad, heavy vehicles | 6 in | 1.85 |
| Shop floor with equipment | 6–8 in | 1.85–2.47 |
Monolithic slabs are the exception. A slab with a thickened perimeter edge isn’t a flat plate — that edge can add 30% or more to the volume. Use our concrete slab calculator, which has a thickened edge mode and returns rebar quantities as well.
What PSI concrete should you order?
Strength is quoted in PSI at 28 days. Ordering higher than you need wastes money; ordering lower than the application requires means the pour cracks or spalls.
| Strength | Typical use |
|---|---|
| 2,500 PSI | Non-structural fill, some footings, walkways in mild climates |
| 3,000 PSI | Patios, sidewalks, shed floors, most footings |
| 3,500–4,000 PSI | Garage slabs, driveways, anything taking vehicle load or freeze-thaw |
| 4,500+ PSI | Heavy-duty floors, structural columns and beams |
Strength doesn’t change the volume the concrete calculator returns, but it does change price — expect $5–$15 per cubic yard between each step. In freeze-thaw climates you’ll also want air entrainment at 5–7%, which is a separate spec from strength and matters more than an extra 500 PSI. You’ll be asked about slump too — 4–5 inches is typical for a slab.
How much does concrete weigh?
Concrete weighs about 150 pounds per cubic foot, which makes a cubic yard roughly 4,050 lb — just over two tons.
Access. A full 10 yard mixer carries around 40,000 lb of concrete plus 25,000 lb of truck. Most residential driveways are not built for 65,000 lb, and cracking your own driveway to pour a patio is an expensive mistake. Suppliers will send partial loads or recommend a pump if you flag access when ordering.
Forms. That weight is hydraulic pressure against your form boards. A 12 inch deep footing form exerts real side load, and blown-out forms mid-pour is the most common way a DIY concrete job goes wrong.
Ordering — what the batch plant will ask
- Cubic yards, to the quarter yard. That’s how they batch.
- PSI — 3,000, 3,500 or 4,000 for most residential work.
- Slump — 4–5 inches for a slab. Don’t add water on site; it permanently reduces strength and voids the supplier’s warranty.
- Air entrainment — 5–7% if your area sees freeze-thaw cycles.
- Aggregate size — 3/4 inch is standard, 3/8 inch for thin sections or tight reinforcement.
- Access and placement — chute reach is only about 12–18 ft from the truck, so say if you need a pump or extra chutes.
Most suppliers allow 5–7 minutes per cubic yard on site and charge standby time after that. A 5 yard load gives you roughly half an hour. Have enough people, wheelbarrows and tools ready before the truck arrives — concrete does not wait.
Seven mistakes this concrete calculator prevents
- Forgetting to convert inches to feet. Multiplying feet by inches gives an answer twelve times too large.
- Using diameter instead of radius in the circle formula — four times too much concrete on post holes.
- Skipping waste entirely, then running short the moment the base has a low spot.
- Treating a monolithic slab as a flat plate. The thickened edge can be a third of the volume.
- Sizing footings above the frost line. Depth is code, not preference, and it changes the yardage a lot.
- Ignoring the pump line. A quarter yard stays in the hose and never reaches the pour.
- Rounding down. Plants sell in quarter yards; always round up to the next quarter.
Frequently asked questions
How do I calculate how much concrete I need?
Multiply length by width in feet, multiply by the thickness in inches divided by 12, then divide by 27 for cubic yards. Add 5–10% for waste and round up to the next quarter yard. For footings use total run × width × depth; for round holes use π × radius² × depth × number of holes.
How many cubic yards of concrete do I need for a 10 × 10 slab?
At 4 inches thick, a 10 × 10 ft slab needs 1.23 cubic yards before waste, so order 1.5 yd³. At 5 inches it’s 1.54 yd³ and at 6 inches 1.85 yd³.
How many square feet does a yard of concrete cover?
81 square feet at 4 inches thick, 108 ft² at 3 inches, 65 ft² at 5 inches and 54 ft² at 6 inches. One cubic yard is 27 cubic feet, so divide 27 by the thickness in feet.
How much concrete do I need per fence post?
A 12 inch diameter hole at 30 inches deep takes about 1.96 cubic feet, roughly 3.3 × 80 lb bags. For eight posts that’s 15.7 ft³ or 0.58 cubic yards. Deeper holes in northern frost zones need considerably more.
How much does a cubic yard of concrete cost?
Ready-mix supply typically runs $130–$180 per cubic yard in most US markets, before pump hire, short-load fees or weekend surcharges. Bagged concrete works out around $270–$400 per cubic yard. Prices vary by region and haul distance.
How much does a concrete truck hold?
A standard mixer carries about 10 cubic yards, though many suppliers cap residential deliveries at 8–9 for weight limits. A full load is roughly 40,000 lb of concrete plus 25,000 lb of truck, which many residential driveways cannot take.
How much does a cubic yard of concrete weigh?
About 4,050 pounds, or just over two tons, based on 150 lb per cubic foot. Cured concrete is marginally lighter once mix water has been consumed and evaporated.
How thick should a concrete slab be?
4 inches suits patios, shed floors and most garage slabs. Driveways run 4–5 inches, RV pads and heavy vehicle areas 6 inches, and shop floors 6–8 inches. Walkways can go down to 3 inches. Structural slabs should follow your local building code.
What PSI concrete do I need?
3,000 PSI covers patios, sidewalks and most footings. Garage slabs and driveways are usually 3,500–4,000 PSI. In freeze-thaw climates, air entrainment at 5–7% matters more than an extra 500 PSI.
How long does concrete take to cure?
Walk on it after 24–48 hours, drive a car on it at around 7 days, and wait 28 days for full design strength and heavy loads. Keeping it damp or covered through the first week matters more to final strength than most people expect.
Is it cheaper to mix your own concrete?
Buying Portland cement, sand and gravel separately is cheaper per yard than bagged mix, but only worth it above about half a cubic yard where you have a mixer and space for loose aggregate. Above roughly 1.2 cubic yards, ready-mix delivered beats both on cost and consistency.
Can I use this concrete calculator in metric?
Yes. Switch the toggle in the calculator header to m / mm and every input changes to metres and millimetres, with 20, 25 and 40 kg bag sizes available. Results are shown in cubic yards, cubic feet and cubic metres together.
Standards and sources
- ACI 318 — Building code requirements for structural concrete
- ACI 332 — Residential concrete construction code
- ACI 301 — Specifications for structural concrete, including mix water limits
- ASTM C94 — Ready-mixed concrete specification, covering slump and delivery time
- Published bag yield data from major concrete mix manufacturers
- Local building department frost depth requirements (vary by jurisdiction)
Related calculators
Concrete Bag CalculatorBag counts for 40, 60 and 80 lb sizes
Post Hole CalculatorBags per post and frost depth guidance
Rebar CalculatorGrid spacing and linear feet
Cubic Yards CalculatorConvert any volume to yd³
Square Footage CalculatorWork out your area first
How this concrete calculator works out its numbers
Volume uses standard geometric formulas with every input normalised to feet before multiplication, then divided by 27 for cubic yards. Step volumes are summed prism by prism, with each tread carrying the risers above it. Weight is calculated at 150 lb per cubic foot and truck loads assume a 10 yd³ mixer. Bag yields are 0.60 ft³ for 80 lb, 0.45 ft³ for 60 lb, 0.375 ft³ for 50 lb and 0.30 ft³ for 40 lb, matching published manufacturer figures; metric equivalents are 0.010 m³ for 20 kg, 0.0125 m³ for 25 kg and 0.020 m³ for 40 kg.
Cost figures use the ready-mix rate you enter and reflect supply only — they exclude pumping, short-load fees, standby time, weekend surcharges, forms, reinforcement and labor.
This concrete calculator produces quantities, not structural design. Slab thickness, reinforcement, footing dimensions and frost protection must follow your local building code, and anything structural should be reviewed by a qualified engineer. Frost depth in particular varies widely by jurisdiction and directly changes how much concrete a footing requires.