How to figure concrete yardage: the formula
Figuring out concrete yardage is one multiplication and one division. Multiply length × width × thickness with everything in feet, then divide by 27.
cubic yards = (length ft × width ft × thickness ft) ÷ 27
27 is the whole trick. A cubic yard is a cube 3 ft on every side, and 3 × 3 × 3 = 27 cubic feet. Every concrete order in the United States is placed in these units, which is why a measurement taken in feet has to be divided down before you can phone it in.
Worked example: a 20 × 20 pad at 4 inches
- Measure in feetLength 20 ft, width 20 ft. Take the tape to the inside faces of the forms, which is where the concrete actually goes.
- Turn inches into feet4 inches ÷ 12 = 0.333 ft. This is the step almost everyone gets wrong: entering 4 instead of 0.333 overstates the pour twelvefold.
- Multiply for cubic feet20 × 20 × 0.333 = 133.3 cubic feet.
- Divide by 27133.3 ÷ 27 = 4.94 cubic yards.
- Add waste and round up4.94 + 10% = 5.43, so order 5.5 cubic yards. Plants sell in quarter-yard steps.
Shortcuts worth memorizing
Once you have the square footage, you do not need a calculator to sanity-check the answer:
4 inch slab: square feet ÷ 81 = cubic yards.
5 inch slab: square feet ÷ 65.
6 inch slab: square feet ÷ 54.
8 inch slab: square feet ÷ 41.
Those divisors come straight out of the formula. One cubic yard spread 4 inches deep covers 81 square feet, because 27 cubic feet divided by 0.333 ft of depth is 81 square feet of floor.
Round shapes swap the first two terms for the area of a circle: π × radius² × height ÷ 27. A 12 inch sonotube 4 ft deep is 3.1416 × 0.5² × 4 = 3.14 cubic feet, or 0.116 cubic yards — six 80 lb bags once you round up (3.14 ÷ 0.60 = 5.2).
How many square feet does a yard of concrete cover?
One cubic yard covers 81 square feet at 4 inches thick. Change the depth and the coverage changes with it, because 324 divided by the thickness in inches gives you the answer every time.
| Thickness | Sq ft per yd³ | Yd³ per 100 sq ft | 80 lb bags per 100 sq ft |
|---|---|---|---|
| 2" | 162.0 | 0.62 | 28 |
| 3" | 108.0 | 0.93 | 42 |
| 4" | 81.0 | 1.23 | 56 |
| 5" | 64.8 | 1.54 | 70 |
| 6" | 54.0 | 1.85 | 84 |
| 8" | 40.5 | 2.47 | 112 |
| 10" | 32.4 | 3.09 | 139 |
| 12" | 27.0 | 3.70 | 167 |
Volumes are neat, before any waste allowance. Highlighted row is the standard residential slab depth.
Square feet are not cubic yards
This trips people up constantly, and it is worth being blunt about: a square foot has no depth, and a cubic yard does. There is no fixed conversion between the two. Asking how many square feet are in a yard of concrete only has an answer once you say how thick the slab is.
At 4 inches thick, each square foot of slab needs 0.0123 cubic yards (1 ÷ 81). A 500 sq ft patio is 500 × 0.0123 = 6.17 cubic yards. Dividing by 81 gets you the same answer and is harder to fumble on a phone keypad: 500 ÷ 81 = 6.17.
Suppliers quote by the cubic yard. Contractors quote by the square foot, typically $6.50 to $10.50 installed for a plain broom finish. When you compare two bids, check which unit each one is using before you decide anything.
Yards of concrete for common slab and pad sizes
The footprints people actually pour, worked out at three depths. Tap any row to load it into the calculator above.
| Slab size | Sq ft | Yd³ @ 4" | Yd³ @ 5" | Yd³ @ 6" | 80 lb bags @ 4" | Ready-mix @ 4" |
|---|---|---|---|---|---|---|
| 8 × 8 ft | 64 | 0.79 | 0.99 | 1.19 | 36 | $115 |
| 10 × 10 ft | 100 | 1.23 | 1.54 | 1.85 | 56 | $179 |
| 10 × 12 ft | 120 | 1.48 | 1.85 | 2.22 | 67 | $215 |
| 10 × 20 ft | 200 | 2.47 | 3.09 | 3.70 | 112 | $358 |
| 12 × 12 ft | 144 | 1.78 | 2.22 | 2.67 | 80 | $258 |
| 12 × 16 ft | 192 | 2.37 | 2.96 | 3.56 | 107 | $344 |
| 15 × 15 ft | 225 | 2.78 | 3.47 | 4.17 | 125 | $403 |
| 16 × 20 ft | 320 | 3.95 | 4.94 | 5.93 | 178 | $573 |
| 20 × 20 ft | 400 | 4.94 | 6.17 | 7.41 | 223 | $716 |
| 20 × 24 ft | 480 | 5.93 | 7.41 | 8.89 | 267 | $859 |
| 20 × 30 ft | 600 | 7.41 | 9.26 | 11.11 | 334 | $1,074 |
| 24 × 24 ft | 576 | 7.11 | 8.89 | 10.67 | 320 | $1,031 |
| 30 × 30 ft | 900 | 11.11 | 13.89 | 16.67 | 500 | $1,611 |
| 30 × 40 ft | 1,200 | 14.81 | 18.52 | 22.22 | 667 | $2,148 |
| 40 × 60 ft | 2,400 | 29.63 | 37.04 | 44.44 | 1,334 | $4,296 |
Ready-mix column uses $145 per cubic yard, the 2026 US national average for 3000 PSI delivered. Small pours will also attract a short-load fee.
Reading the table on site
A 20 × 20 slab is the one people search for most, usually a two-car parking pad or a shop floor. At 4 inches it is 4.94 cubic yards; at 6 inches, which is what you want under vehicles, it jumps to 7.41. That is a 50 percent increase in concrete for two extra inches of depth.
Anything in the 30 × 30 range and up is past a single truck load once you add waste, so plan for two deliveries and have the crew ready before the first truck arrives. Concrete has to be placed within about 90 minutes of water hitting the mix.
Odd shapes
An L-shaped or stepped pour is just two rectangles. Split it on paper, run each piece through the calculator, and add the results. Do not try to average the dimensions — that quietly loses volume at the corner.
For a footprint with a curve, take the smallest rectangle that contains the whole shape, calculate that, then subtract the corner pieces you are not pouring. Overestimating on a curved edge is cheap insurance.
Concrete for footings, sonotubes, round slabs, stairs and walls
Every shape comes back to the same rule: find the volume in cubic feet, then divide by 27. Only the first step changes.
Sonotube and pier volume
| Tube diameter | Cu ft per ft of depth | Cu ft at 4 ft | 80 lb bags at 4 ft |
|---|---|---|---|
| 6" | 0.20 | 0.79 | 2 |
| 8" | 0.35 | 1.40 | 3 |
| 10" | 0.55 | 2.18 | 4 |
| 12" | 0.79 | 3.14 | 6 |
| 16" | 1.40 | 5.59 | 10 |
| 18" | 1.77 | 7.07 | 12 |
| 24" | 3.14 | 12.57 | 21 |
Deck and fence footings are almost always bagged: even ten 12" piers at 4 ft come to barely over one cubic yard.
Round slabs
Use π × radius² for the area, then multiply by thickness. A 12 ft diameter fire-pit patio at 4 inches is 3.1416 × 6² × 0.333 = 37.7 cubic feet, or 1.40 cubic yards.
Strip footings
Treat a footing as a long, narrow slab: total run × width × depth. A 40 ft run of 18 inch wide by 12 inch deep footing is 40 × 1.5 × 1 = 60 cubic feet, or 2.22 cubic yards. Use a 10 percent waste allowance, since trenches are rarely dug perfectly square.
Poured concrete stairs
For solid steps poured on grade, each step is a block that runs all the way down to the ground, so the volume is width × run × rise × n(n+1) ÷ 2, where n is the number of steps. Four steps with a 7 inch rise, 11 inch run and 4 ft width come to 21.4 cubic feet, or 0.79 cubic yards — about 36 bags of 80 lb mix.
Walls
Length × height × thickness. A 30 ft stem wall 4 ft high and 8 inches thick is 30 × 4 × 0.667 = 80 cubic feet, or 2.96 cubic yards. Walls usually need a pump or a long chute, so price the pump before you book the truck.
How many bags of concrete are in a yard?
It takes 45 bags of 80 lb concrete mix to make one cubic yard. Each 80 lb bag yields 0.60 cubic feet, a cubic yard holds 27 cubic feet, and 27 ÷ 0.60 = 45.
| Bag size | Yield (cu ft) | Bags per yd³ | Sq ft @ 4" per bag | $ per yd³ |
|---|---|---|---|---|
| 80 lb | 0.600 | 45 | 1.80 | $281 |
| 60 lb | 0.450 | 60 | 1.35 | $327 |
| 50 lb | 0.375 | 72 | 1.13 | $356 |
| 40 lb | 0.300 | 90 | 0.90 | $392 |
Bag prices are typical 2026 big-box shelf prices and move around by region.
When bags beat a truck
Bagged mix costs roughly double ready-mix per cubic yard, but it carries no delivery charge, no minimum order and no short-load fee. That changes the arithmetic on small pours.
Under 0.5 yd³ — bags, comfortably. That is about 23 bags of 80 lb, one afternoon, one wheelbarrow.
0.5 to 1 yd³ — a judgment call. Mixing 45 bags by hand is a genuinely hard day.
Over 1 yd³ — call the plant. Even with a short-load fee, ready-mix usually wins on cost and always wins on finish.
The other argument for a truck is consistency. Every bag you mix by hand has a slightly different water content, and water content is what sets the final strength. A batch plant holds the water-cement ratio to a specification you can put on paper.
If you do go with bags, follow the water amount printed on the bag (roughly 3 quarts per 80 lb bag for most standard mixes), added gradually. Mix to the consistency of thick oatmeal. Extra water makes the mix easier to place and measurably weaker.
How much is a yard of concrete in 2026?
Ready-mix runs about $125 to $180 per cubic yard delivered, with a national average near $145 for standard 3000 PSI residential mix. Strength, distance from the plant and order size move that number more than anything else.
| Mix | Typical use | Per yd³ |
|---|---|---|
| 2500 PSI | Non-structural fill, mud slabs | $120 - $140 |
| 3000 PSI | Patios, sidewalks, shed pads, most residential | $130 - $155 |
| 3500 PSI | Driveways, garage floors | $140 - $165 |
| 4000 PSI | Footings, foundation walls, heavy traffic | $150 - $180 |
| 5000 PSI | Commercial floors, freeze-thaw exposure | $165 - $200 |
| Fiber-reinforced | Add-on to any mix, reduces shrinkage cracks | +$8 - $15 |
Material and delivery within roughly 15 to 20 miles of the plant. Labor to place and finish is separate.
The charges that are not on the quote
The per-yard price is the start of the invoice, not the end. Ask about all of these before you book:
| Charge | When it applies | Typical |
|---|---|---|
| Short-load fee | Order below the plant minimum, usually 5–10 yd³ | $50–$250 |
| Waiting time | Past the free unload window, about 5–7 min per yard | $1–$3/min |
| Pump truck | Chute cannot reach; backyards, basements, long runs | $500–$1,500 |
| Saturday delivery | Weekend pours at most plants | $8–$10/yd³ |
| Winter mix | Heated water and cold-weather admixtures | $5–$7/yd³ |
| Mileage | Beyond the included delivery radius | $5–$15/yd³ |
On a 3 yard pour a $120 short-load fee is $40 per yard on top of the sticker price — a 28 percent increase. Ordering up to the plant minimum is sometimes cheaper than paying the fee. Ask the dispatcher to price it both ways.
Ordering: truck loads, waste and slab thickness
How much concrete a truck holds
A standard ready-mix truck carries 8 to 11 cubic yards, and 9 to 10 is the load most plants actually run. The drum holds 14 or 15, but nobody fills it: road weight limits and mix workability both cap it well short. A 10 yard load is about 40,000 lbs of concrete riding on a 26,000 lb truck, which is worth thinking about before it drives across your existing driveway.
Divide your waste-adjusted yardage by 10 and round up to get your load count. If the answer lands just over a whole number — 10.4 yards, say — talk to the dispatcher. Trimming the slab by half an inch or accepting a slightly richer waste factor on one load is cheaper than sending a truck out for 0.4 yards.
How much extra to order
Add 5 to 10 percent. Five percent for a small slab on a flat, compacted, screeded base with stiff forms. Ten percent for footings, trenches, sloping ground, or anything where the forms could bow outward under load.
Small errors add up fast on a big pour: on a 30 × 40 slab, a subgrade just a quarter inch low across the whole area swallows almost an extra cubic yard. Over-excavated footings do the same. Running short in the middle of a pour leaves you with a cold joint and a permanent weak line through the slab; the extra concrete costs a few dollars.
How thick should the slab be?
| Application | Thickness | Mix |
|---|---|---|
| Walkway, garden path | 3–4" | 3000 PSI |
| Patio, shed floor | 4" | 3000 PSI |
| Standard car driveway | 4" | 3500 PSI |
| Driveway with trucks or RV | 5–6" | 4000 PSI |
| Garage, workshop floor | 5–6" | 4000 PSI |
| Hot tub or equipment pad | 6" | 4000 PSI |
| Footing, structural pad | 8–12" | 4000 PSI |
Thickness costs more than footprint. Going from 4 to 5 inches on any slab adds 25 percent to the concrete volume. Going from 4 to 6 adds 50 percent. Get the depth decision right before you price anything.
None of this replaces your local building code. Frost depth, expansive soils and anything holding up a structure are code matters, and the inspector's number is the one that counts.
Concrete yardage questions, answered
How do I figure out concrete yardage?
Multiply length by width by thickness with every measurement in feet, then divide the result by 27. A 20 ft by 20 ft pad at 4 inches thick is 20 x 20 x 0.333 = 133.3 cubic feet, and 133.3 divided by 27 equals 4.94 cubic yards. Add 5 to 10 percent for waste and order 5.5 yards. The only step people get wrong is the thickness: 4 inches has to be entered as 0.333 feet, not 4.
How many yards of concrete do I need?
It depends entirely on footprint and thickness, but for a 4 inch slab a fast field check is square footage divided by 81. A 400 square foot patio at 4 inches needs about 4.9 cubic yards. At 6 inches thick, divide square footage by 54 instead. Enter your real dimensions in the calculator above for an exact figure including waste.
How many square feet does a yard of concrete cover?
One cubic yard covers 81 square feet at 4 inches thick, 65 square feet at 5 inches, 54 square feet at 6 inches, and 41 square feet at 8 inches. The formula is 324 divided by the thickness in inches, because a cubic yard contains 27 cubic feet and there are 12 inches in a foot.
How many 80 lb bags of concrete are in a yard?
It takes 45 bags of 80 lb concrete mix to make one cubic yard. Each 80 lb bag yields 0.60 cubic feet and a cubic yard holds 27 cubic feet, so 27 divided by 0.60 equals 45. A 60 lb bag yields 0.45 cubic feet, so you would need 60 of those. A 50 lb bag needs 72 and a 40 lb bag needs 90.
How much is a yard of concrete?
Ready-mix concrete runs roughly $125 to $180 per cubic yard delivered in 2026, with a national average near $145 for standard 3000 PSI residential mix. Short-load fees of $50 to $250 apply below the supplier minimum, which is usually 5 to 10 yards, so a 2 yard pour often costs far more per yard than the sticker price suggests.
How many cubic feet are in a cubic yard of concrete?
There are exactly 27 cubic feet in one cubic yard. A cubic yard is a cube measuring 3 feet on every side, and 3 x 3 x 3 equals 27. This single number is what turns a measurement in feet into an order you can place with a ready-mix plant.
How much concrete does a truck hold?
A standard ready-mix truck carries 8 to 11 cubic yards, with 9 to 10 being the usual working load. The drum itself holds 14 to 15 yards but is never filled to capacity because of road weight limits and mix workability. A full 10 yard load weighs about 40,000 lbs of concrete on top of the 26,000 lb truck.
How much extra concrete should I order for waste?
Add 5 to 10 percent on top of your calculated volume. Use 5 percent for a small, well-formed slab on a flat compacted base, and 10 percent for footings, uneven subgrade, or anything where the forms might bow. Running short mid-pour creates a cold joint you cannot undo, while a little extra concrete costs a few dollars.
Is it cheaper to use bags or ready-mix concrete?
Bags win under about 0.5 cubic yards and ready-mix wins above roughly 1 cubic yard. Bagged mix works out to about $280 to $390 per cubic yard in material alone, depending on bag size, versus $125 to $180 for delivered ready-mix, but bags have no delivery fee, no minimum order and no short-load charge. Between 0.5 and 1 yard the decision comes down to how much mixing labor you have available.
How thick should a concrete slab be?
Use 4 inches for patios, walkways, shed floors and standard driveways. Go to 5 or 6 inches for driveways that see trucks or RVs, garage floors and workshop slabs. Footings and structural pads typically run 8 to 12 inches. Every extra inch on a 4 inch slab adds 25 percent to the concrete volume, so thickness drives cost harder than footprint does.
How much does a yard of concrete weigh?
One cubic yard of normal-weight concrete weighs about 4,050 lbs, or roughly 2 tons. That works out to 150 lbs per cubic foot. This matters for access planning: a loaded ready-mix truck can crack a residential driveway or sink into soft ground.
How many yards of concrete for a 20x20 slab?
A 20 ft by 20 ft slab needs 4.94 cubic yards at 4 inches thick, 6.17 yards at 5 inches, and 7.41 yards at 6 inches. With a 10 percent waste allowance you would order 5.5, 7 or 8.25 yards respectively. Suppliers usually sell in quarter-yard increments, so always round up to the next quarter.