How much concrete
do you actually need?
Pick your shape, drop in the measurements, and get the exact volume, the number of bags, and a ready-mix cost estimate — with waste allowance built in, so you never run short mid-pour.
1 · Shape & measurements
Results update as you type. All volumes include your waste allowance where noted.
Rectangular slab
2 · Quantity & waste
Pouring more than one? Set the quantity — footing runs, columns and identical slabs multiply automatically.
Pros order 5–10% extra for slabs on grade, 10–15% for footings in uneven trenches. Running short costs far more than a little extra.
3 · Bag size & prices
Used for the bag count and cost comparison. Edit the prices to match your local store or supplier.
Exact volume before waste: 0.00 yd³ · Slab × 1
Bags by size — same pour
How the maths works
Every result above comes from one idea: volume = the space the pour fills. Measure in feet, multiply, then divide by 27 to get cubic yards — the unit ready-mix trucks sell by.
Length × Width × Thickness
A 10 × 10 ft patio at 4 inches thick is 10 × 10 × 0.333 = 33.3 ft³, which is 1.23 yd³. Thickness is where most people slip up — always convert inches to feet first (inches ÷ 12).
π × Radius² × Depth
For circles, halve the diameter to get the radius, square it, and multiply by π (3.1416) and the depth. A 12 ft diameter pad, 4 in thick: 3.1416 × 6² × 0.333 = 37.7 ft³ ≈ 1.40 yd³.
Each step stacks on the last
Step 1 is one rise tall, step 2 is two rises, and so on. Total volume = width × tread × riser × (1 + 2 + … + n). Four steps add up much faster than most people expect.
Bag yield reference
One bag never covers a full cubic foot. These are the standard yields for premixed concrete bags — the same numbers this calculator uses.
| Bag size | Yield per bag | Bags per ft³ | Bags per yd³ | Bags per m³ |
|---|---|---|---|---|
| 40 lb (18.1 kg) | 0.30 ft³ | 3.33 | 90 | 118 |
| 50 lb (22.7 kg) | 0.375 ft³ | 2.67 | 72 | 94 |
| 60 lb (27.2 kg) | 0.45 ft³ | 2.22 | 60 | 79 |
| 80 lb (36.3 kg) | 0.60 ft³ | 1.67 | 45 | 59 |
Rule of thumb: once a pour passes about 1 yd³ (45 × 80 lb bags), hand-mixing stops being fun and a truck starts making sense.
Bags or ready-mix truck?
The calculator prices both for your exact pour. Which one wins depends on size, access and how much your back is worth.
Premix bags
- No minimum order, no delivery window to hit
- Mix only what you need, when you need it
- Cheapest for small repairs, posts and pads
- Heavy work: an 80 lb bag covers just 0.6 ft³
- Risk of cold joints if you mix too slowly
Ready-mix truck
- One continuous pour — stronger, more consistent
- Far cheaper per yard at volume
- Typical minimum order is 1 yd³, short-load fees below that
- You need the forms, crew and finishing tools ready when it arrives
- Standard truck carries about 8–10 yd³
Before you order
Measure the real trench, not the plan
Footings dug by hand or machine are almost always wider and deeper than drawn. Measure the actual excavation in three places and use the average — that is what the waste slider is compensating for.
Subgrade eats concrete
An uneven base can quietly add half an inch of thickness across a whole slab. Compact and level the gravel base, and check depth with a string line before the truck is booked.
Round up, never down
Suppliers would rather take back a quarter yard than send a second truck for a shortfall. Order to the nearest quarter yard above your with-waste figure, and have a backup spot (a small pad, post holes) ready for any leftover.
Common questions
How many bags of concrete do I need for a 10×10 slab?
At the standard 4-inch thickness, a 10×10 ft slab is 1.23 yd³ (33.3 ft³). That works out to roughly 56 bags of 80 lb, 74 bags of 60 lb, or 111 bags of 40 lb — before waste. Add 10% and most people order a truck instead: it is one phone call versus fifty-plus bags through a mixer.
How thick should my slab be?
4 inches is standard for patios, walkways and shed bases. Go 5–6 inches for driveways and anywhere a car will park, and 6 inches or more with rebar or mesh for heavy vehicles and garage floors. Footings in cold climates must also reach below the frost line — check your local code.
Why does the calculator add waste?
Because real pours are never perfect boxes: trenches over-dig, forms bow, subgrade dips, and some concrete stays in the wheelbarrow and pump. A 10% allowance absorbs all of that. Running short mid-pour leaves a cold joint — a permanent weak seam — so the extra is cheap insurance.
How do I convert cubic feet to cubic yards?
Divide by 27. One cubic yard is 3 ft × 3 ft × 3 ft = 27 ft³. For metres: one cubic yard is 0.765 m³, and one cubic metre is 1.31 yd³. This calculator shows all three at once so you can order in whichever unit your supplier uses.
How much does a yard of concrete weigh?
About 4,050 lb (roughly 2 tons) per cubic yard when cured, or about 150 lb per cubic foot. That matters for trailers and pickup beds: a single yard in bags is around 3,600 lb of dry mix before you add water — well past most half-ton truck payloads in one trip.
What strength (PSI) should I order?
2,500–3,000 PSI covers most residential flatwork (patios, sidewalks). Driveways and garage floors are usually 3,500–4,000 PSI, often with air entrainment in freeze–thaw climates. Footings commonly run 2,500–3,500 PSI. Your supplier can match the mix to the job — tell them what it is for.
Related tools
The pour is only part of the job — these pages cover the rest of it.
How many bags of concrete?
Enter the pour size and get the bag count for every standard premix size at once — with waste included, so the last corner doesn't run short.
Your measurements
Results update as you type.
Yields used: 40 lb = 0.30 ft³, 50 lb = 0.375 ft³, 60 lb = 0.45 ft³, 80 lb = 0.60 ft³ per bag.
The maths
Volume first, bags second: length × width × thickness gives cubic feet; divide by the yield of the bag size you are buying.
ft³ ÷ yield per bag
A 10 × 10 ft slab at 4 in is 33.3 ft³. In 80 lb bags: 33.3 ÷ 0.60 = 56 bags before waste — 62 with 10% added.
When bags stop making sense
Past about 1 yd³ (45 × 80 lb bags) the lifting, mixing and cold-joint risk usually outweigh the saving. Compare on the cost page.
Round is different
For post holes and round pads, use the column or round-slab shapes on the main concrete calculator.
What will the concrete cost?
Price the same pour both ways — ready-mix truck against bags mixed on site — using your local prices. The truck figure includes the 1 yd³ minimum and your delivery fee.
Your measurements
Results update as you type.
Truck total = max(volume, 1 yd³) × price + delivery. Short-load fees vary by supplier — ask before booking under 3 yd³.
Reading the result
Bags win on small pours because there is no minimum order or delivery fee. The truck wins on price per yard almost as soon as the pour passes a yard or two.
Don't forget the hidden costs
Bags need a mixer rental, water and hours of labour; a truck needs forms finished, a crew ready, and sometimes a pump ($150–$250 typical). Price the whole job, not just the material.
Get your volume first
Not sure of the yardage? Work it out on the concrete calculator, then bring the number back here.
Prices are local
Ready-mix commonly runs $140–$200 per yd³ and 80 lb bags $5–$8, but both swing by region. The defaults here are editable — use your supplier's real quote.
Concrete footing calculator
Strip footings under walls, fences and decks. Enter the actual dug trench — length, width and depth — and get the exact volume, bag count and weight for the whole run, waste included.
Footing measurements
For a continuous trench footing. Results update as you type.
Typical strip footing: 16–24 in wide × 8–12 in deep. In cold climates the bottom must sit below the frost line — often 36–48 in deep overall.
Formula: length × width × depth ÷ 27 = yd³. Footings almost always over-dig — 10–15% waste is normal here, more than for a slab.
How to size & pour a footing
A footing spreads the wall's load over a wider strip of soil so the structure doesn't settle. Getting the width, depth and trench condition right matters more than the last quarter-yard of concrete.
L × W × D ÷ 27
A 40 ft trench, 16 in wide × 12 in deep: 40 × 1.33 × 1 = 53.3 ft³ = 1.98 yd³ before waste — about 2.17 yd³ with 10% added. Convert width and depth from inches to feet first (÷ 12).
Width & depth guide
One-storey walls commonly sit on a 16 in wide footing, two-storey on 20–24 in. Depth of concrete is usually 8–12 in, but the trench bottom must be on undisturbed soil and below the frost line where codes require it. Always check local code — footing sizes are inspected.
Measure the dug trench
Hand- and machine-dug trenches flare wider than the plan. Measure width and depth in three places and average them here. Pouring against neat, compacted trench walls (no loose spoil at the bottom) saves concrete and makes a stronger footing.
Before you order for a footing
Steel in the footing
Most strip footings carry two continuous runs of #4 rebar. Work out lengths on the rebar page using the trench length.
Wall on top?
If a stem or foundation wall sits on this footing, size that pour next on the main concrete calculator (Wall shape).
Bags or truck?
A 40 ft strip footing is already ~2 yd³ — about 90 × 80 lb bags. Price both ways on the cost page before deciding.
Concrete slab calculator
Patios, driveways, shed bases and garage floors. Length, width and thickness is all it takes — get cubic yards, bag counts for every pour size, and the area you're covering.
Slab measurements
For a flat rectangular slab. Results update as you type.
Formula: length × width × (thickness ÷ 12) ÷ 27 = yd³. Thickness is entered in inches and converted for you.
Slab thickness & prep guide
Most slab failures are thickness and base problems, not concrete problems. Pick the thickness for the load, then spend as much care on what's underneath as on the pour itself.
Patios, paths & shed bases
The residential standard for foot traffic. A 12 × 10 ft patio at 4 in is 1.48 yd³ before waste — about 74 × 80 lb bags, which is why most people order a truck even at this size.
Driveways & parking
Go 5–6 in anywhere a car parks, and add a rebar grid or mesh — count the steel on the rebar page. Garage floors are typically 6 in.
Base & subgrade
Pour over 4 in of compacted gravel (size it on the gravel page), check depth with a string line, and dampen the base before pouring so it doesn't pull water out of the mix.
Ordering a slab pour
Round up to the quarter yard
Suppliers dispatch in quarter-yard steps. Order the with-waste figure rounded up, and have a small backup form ready (a pad or post holes) for any leftover.
Control joints
Plan joints every 8–12 ft in both directions on a 4 in slab, cut within 24 hours. Joints don't stop cracking — they decide where it happens neatly.
Round slab instead?
For a circular pad, hot-tub base or fire-pit area, use the Round slab shape on the main concrete calculator.
Concrete column calculator
Round columns, deck posts, fence posts and sonotube piers. Enter the tube diameter and depth once, set how many posts you're pouring, and get the total — plus the per-column figure for mixing bag-by-bag.
Column measurements
For round columns and post holes. Results update as you type.
Post holes should reach below the frost line — commonly 36–48 in deep in cold climates. Diameter is the hole / tube size, not the post itself.
Formula per column: π × (diameter ÷ 2)² × height ÷ 27 = yd³, then × number of posts. Diameter is converted from inches for you.
Column & post-hole guide
A column's volume grows with the square of its diameter — stepping from a 10 in to a 12 in tube adds 44% more concrete, not 20%. This guide keeps the sizing honest.
π × r² × height
One 12 in diameter pier, 3 ft deep: π × 0.5² × 3 = 2.36 ft³ ≈ 0.09 yd³ — about 4 × 80 lb bags. Six of them is 0.52 yd³ before waste, 0.58 yd³ with 10% added — about 26 bags in total.
Choosing a diameter
8 in tubes suit fence posts and light decks, 10–12 in covers most deck and pergola posts, 16 in and up is for heavier loads and structural piers. The footing at the bottom is often belled wider than the tube — add that extra volume as waste or measure it separately.
Depth & frost
The bottom of the pier must sit below the frost line and on firm soil, or frost heave will lift it. Check your local depth requirement before digging — it's the single most common post-hole mistake.
Pouring posts & piers
Bags usually win here
Individual holes are a classic bag job — mix per hole using the bags-per-column figure above. Compare a truck only when the total passes ~1 yd³, on the cost page.
Set hardware while it's wet
Post bases and J-bolts go in while the concrete is workable. Brace posts plumb in both directions and don't load them for at least 48 hours.
Square column instead?
For a square pier or block column, use length × width × height on the main concrete calculator (Slab / Wall shapes work for square sections).
Rebar calculator
Steel grid for a slab or footing pad: how many bars each way, total linear feet, 20 ft sticks to buy, and the weight of steel going in.
Your measurements
Results update as you type.
Assumes a single grid, 3 in edge cover each side, bars cut from 20 ft stock. Driveways typically use #4 at 18–24 in; structural slabs follow the engineer's schedule.
How the grid is counted
Bars are counted in both directions: the number that fit across the width at your spacing, times the slab length — and vice versa — less 3 in of concrete cover at each edge.
Count = (width − 6″) ÷ spacing + 1
Each direction is counted separately, then lengths are summed. 10% is added for lap splices (bars overlap ~24× their diameter) and cutting waste.
Chairs matter
Steel only works in the middle-to-lower third of the slab. Rest the grid on chairs or dobies — rebar left lying on the gravel does almost nothing.
Volume first
Pair this with the slab page for the concrete itself, and the gravel page for the base under it.
Gravel & aggregate calculator
Base under a slab, a driveway top-up, or bedding for pavers — get cubic yards, tons and bags for the material you pick.
Your measurements
Results update as you type.
Densities are typical loose-to-compacted averages; your supplier's actual tonnage per yard can vary ±10% with moisture and stone type.
Depth guide
The depth you enter drives everything. These are the usual compacted depths — enter the loose depth a little higher if you are compacting in layers.
4 in — slab base
Standard compacted gravel base under patios, walkways and shed slabs. Compact in 2 in lifts with a plate compactor.
4–6 in — driveways
More for cars and soft soil. On clay, go deeper and consider a geotextile fabric to stop the stone migrating into the soil.
1 in — paver bedding
Bedding sand is screeded at exactly 1 in over the compacted base — the paver page works this out with the pavers.
Cement mix calculator
Mixing on site instead of buying premix bags? Pick a ratio and get the cement bags, sand, aggregate and water for your volume.
Your measurements
Results update as you type.
Uses the standard dry-volume factor of 1.54 (dry ingredients shrink when mixed) and 94 lb of cement = 1 ft³. Water is a starting point — add slowly to a workable slump.
Why the dry factor?
Loose dry cement, sand and stone contain air voids. Wet and mixed, they pack down — so you need about 1.54 ft³ of dry material for every 1 ft³ of finished concrete.
One yard at 1:2:3
27 ft³ × 1.54 ÷ 6 parts = 6.9 ft³ of cement ≈ 7 bags, with roughly 0.69 tons of sand and 1.1 tons of aggregate.
Water discipline
Extra water is the easiest way to weaken a mix. Aim for a stiff, workable consistency — about 6 gallons per bag of cement as a ceiling for general work.
Premix instead?
For small jobs, premix bags skip the ratio maths entirely — the bags page counts them for you.
Paver calculator
Pavers for a patio, path or driveway — count, bedding sand and the edge restraint to hold it all in place.
Your measurements
Results update as you type.
Pattern matters: herringbone and diagonal layouts cut more pavers — use 15% waste there instead of 10%.
The build-up under pavers
Pavers are only the top layer: compacted gravel base (4 in for patios, 6 in for driveways), then a screeded 1 in bed of coarse sand, then the pavers, then jointing sand swept in.
Base first
Work out base tonnage on the gravel page using the same length and width at 4–6 in deep.
Edges are not optional
Without edge restraint the field of pavers creeps outward and joints open. Budget the full perimeter in edging or a concrete haunch.
Order a few spares
Keep 5–10 spare pavers from the same batch — dye lots vary, and a cracked paver years later is a 2-minute swap if the colour matches.
Brick calculator
Bricks and mortar for a single-wythe wall, using modular bricks with a standard 3/8 in mortar joint.
Your measurements
Results update as you type.
Modular brick: 7⅝ × 2¼ in face. One brick + joint covers 8 × 2⅝ in = 6.86 bricks per ft². Double-wythe (two bricks thick)? Double the count.
Before you order
Openings come off the area first: subtract doors and windows (length × height) from the wall area, then add waste back for cuts and breakage.
Area × 6.86
A 20 × 6 ft wall is 120 ft² × 6.86 = 823 bricks before waste — about 906 with 10% added.
Mortar yield varies
Joint thickness and how full the joints are change mortar use a lot. The per-bag figures here are mid-range estimates — confirm against the bag's own coverage table.
Concrete footing below
A brick wall needs a footing under it — size it on the footing page.
Asphalt calculator
Hot-mix tonnage for a driveway, parking pad or patch. Asphalt is sold by the ton, compacted — this converts your area and thickness straight to tons.
Your measurements
Results update as you type.
Uses compacted hot-mix density of 145 lb/ft³. Thickness is the compacted figure — loose mix is laid roughly 20–25% thicker and rolled down.
Thickness guide
Residential asphalt fails from a thin mat or a weak base far more often than from the mix itself.
2 in — overlay only
A resurfacing lift over sound existing asphalt. Not a fix for a failed, cracking base — those problems reflect straight through.
3 in — standard driveway
The usual residential spec over 4–6 in of compacted gravel base (size the base on the gravel page).
4 in+ — heavy use
For regular heavy vehicles, RV parking or turning areas where tyres scrub the surface.
About us
Concrete Calculator Easy is a free set of concrete calculators — one focused page per job — built to answer the question every pour starts with: how much do I actually need?
What this site does
Ordering too little concrete leaves a cold joint and a second delivery bill; ordering far too much wastes money. These tools do the volume, bag, cost and materials maths for you, with waste allowance built in, so you can order once and pour once.
Every tool on its own page
The main concrete calculator covers 7 shapes, and there are dedicated pages for bags, cost, footings, slabs, columns, rebar, gravel, cement mix, pavers, brick and asphalt — each with its own formula and guide.
For DIYers and pros alike
First-time patio builders get step-by-step guidance on thickness, base prep and ordering. Experienced crews get the numbers fast — cubic yards, metres and feet side by side, in imperial or metric, with editable local prices.
Standard figures, shown openly
Every result uses published standard values — bag yields (an 80 lb bag = 0.60 ft³), about 4,050 lb per cubic yard cured, compacted asphalt at 145 lb/ft³ — and each page shows the formula it used, so you can check the maths yourself.
How to use the site
Start with volume
Pick the tool that matches your job and enter the real measurements — the dug trench, the actual slab — not just the drawing.
Add the extras
Steel, base gravel and bedding are separate pages on purpose: they are separate orders from separate suppliers.
Compare before you order
Use the cost calculator to price bags against a ready-mix truck with your local prices, then confirm the final quantity with your supplier.
A note on accuracy
These calculators give planning estimates based on standard yields and densities. Real pours vary with subgrade, trench shape, moisture and supplier practices — so treat the results as a well-worked estimate, verify final quantities with your supplier before ordering, and follow your local building code for footings, frost depth and structural work. Nothing here replaces an engineer's design where one is required.
Questions or a correction?
Spotted a figure that looks off, or a tool you wish existed? Tell us on the contact page — corrections and tool requests are genuinely read.
Contact us
Questions about a calculation, a correction to a guide, or an idea for a new tool — send a message and it will be read. The form opens your own email app with everything filled in, addressed to contact@concretecalculatoreasy.com.
Send a message
All fields help us answer faster — the tool and your measurements matter most for calculation questions.
Calculation question?
Include the tool name and your exact measurements. Nine times out of ten the issue is thickness entered as inches vs feet, or a trench that was dug wider than planned — the main calculator's guide sections may already answer it.
Correction or suggestion
If a yield, density or guide figure looks wrong, say which page and what value you expected. Figures here use standard published values, and confirmed corrections get applied.
Prefer email directly?
Write to contact@concretecalculatoreasy.com. Please don't send payment details or order numbers for a concrete supplier — this site sells nothing and can't change an order; your supplier is the right contact for that.