Concrete Calculator
Estimates only. Confirm quantities with your supplier before ordering.
Concrete is estimated by volume: one cubic yard (27 cubic feet) covers about 81 square feet at 4 inches thick and weighs roughly 4,050 pounds. A 10 × 10 ft slab at 4 inches needs about 1.25 cubic yards of ready-mix, or roughly 56 eighty-pound bags. Set your shape, dimensions, and thickness below for exact cubic yards, bag count, weight, and cost.
Concrete bags per cubic yard by bag size
| Bag size | Yield per bag (ft³) | Bags per cubic foot | Bags per cubic yard | Best for |
|---|---|---|---|---|
| 40 lb | 0.30 | 3.3 | 90 | Post setting, small repairs |
| 50 lb | 0.375 | 2.7 | 72 | Small pads, repairs |
| 60 lb | 0.45 | 2.2 | 60 | Footings, small slabs, posts |
| 80 lb | 0.60 | 1.7 | 45 | Slabs and the largest common bag |
How to estimate concrete
Concrete is estimated by volume, then split into whichever unit you'll order in — cubic yards for ready-mix, or bag count for a hand mix. Multiply length by width by thickness with every dimension in feet to get cubic feet, then divide by 27 for cubic yards. The shortcut this calculator runs for a slab is length × width × (thickness ÷ 12) ÷ 27, or, straight from a measured area, square feet × thickness in inches ÷ 324. A 10 × 10 ft slab at 4 inches works out to 33.3 cubic feet, about 1.23 cubic yards — which you'd order as 1.25 yd³ of ready-mix or mix from roughly 56 eighty-pound bags.
Thickness is the input people get wrong
Volume scales directly with thickness, so a half-inch of extra depth across a big slab is real money. Use 4 inches for a patio, shed floor, or walkway; 5 to 6 inches for a driveway or anything carrying vehicles; and whatever your local code specifies for footings, which varies with load and frost depth. Enter the finished thickness you're building to — the presets above seed a common value for each element, but the number your engineer or building department gives you always wins.
Bags or ready-mix?
This is the decision that changes your order. Bagged mix suits small pours — posts, small pads, and repairs up to about half a cubic yard — because you can buy it, store it, and mix it as you go. Past roughly one cubic yard, which is 45 eighty-pound bags, ready-mix delivery is usually cheaper per yard, dramatically less labor, and gives one continuous pour with no cold joints between batches. The calculator shows the bag count and the yardage together so you can price both; near a yard, get a delivered quote before you buy a pallet of bags.
Slabs, footings, and round columns
A slab, patio, or driveway is a simple rectangle — length, width, and thickness. A footing is the same rectangle stood on edge: enter its length and set the thickness field to the footing depth. A column, pier, or form tube such as a Sonotube is a cylinder, so choose the circle shape, enter the tube diameter, and set the thickness field to the pour height (switch its unit to feet). When you're pouring several identical elements — a row of deck footings or fence-post holes — use the quantity field to multiply them in one estimate instead of running the calculator once per hole. If you're reinforcing the pour, the rebar calculator sizes the bar for a slab or footing, and if the footing carries a block wall, the concrete block calculator gives the block and mortar counts for the courses above it.
Don't forget the base and the reinforcement
Concrete rarely goes straight on soil. Slabs and driveways sit on 4 or more inches of compacted crushed stone that spreads the load and drains water away from the underside — size that layer with the gravel calculator. Most slabs also carry reinforcement, either welded wire mesh or a rebar grid, and thickened edges where they'll be loaded. These don't change the concrete volume much, but skipping the base or the steel is the usual reason a slab cracks or heaves within a few winters.
What concrete costs
As of 2026, ready-mix concrete runs about $140 to $180 per cubic yard for the material before delivery, with a short-load fee on orders under roughly 3 to 4 yards that can add $50 to $150. Bagged mix is around $5 to $8 per 80-pound bag — convenient, but several times the price per yard of a delivered load, which is why bags only pencil out on small jobs. A finished slab, once you add forming, reinforcement, placing, and finishing labor, typically lands at $6 to $12 per square foot installed. Enter your local price per yard or per bag in the Ordering section to turn the volume into a material total; the ranges here swing by region and season, so confirm with a plant before you pour.
Common mistakes
- Ordering short with no waste. Running out mid-pour forces a cold joint or a second delivery. Add 5 to 10 percent — the overage field does this — and ready-mix is rounded up to the next quarter yard, the increment plants actually sell in.
- Sizing bags by weight instead of yield. An 80-pound bag does not make 80 ÷ 150 cubic feet of concrete; its published set yield is about 0.60 cubic feet. The bag table above uses the real per-bag yields, which is why 45 eighty-pound bags — not the weight math — make a cubic yard.
- Irregular shapes. This calculator handles rectangles and circles. For an L-shaped slab or a stepped footing, split it into simple sections, run each, and add the cubic yards together before you add waste.
Frequently asked questions
How much concrete do I need for a slab?
Multiply the slab's length by width by thickness (all in feet) to get cubic feet, then divide by 27 for cubic yards. A 10 × 10 ft slab at 4 inches thick is 100 × 0.333 = 33.3 cubic feet, or about 1.23 cubic yards — round that up to 1.25 yd³ for a ready-mix order. As bags, the same slab takes about 56 eighty-pound bags. Enter your real dimensions above and the calculator returns cubic yards, bag count, weight, and cost together, with a waste allowance built in.
How many bags of concrete make a cubic yard?
A cubic yard is 27 cubic feet, so it takes 45 eighty-pound bags, 60 sixty-pound bags, 72 fifty-pound bags, or 90 forty-pound bags of standard concrete mix. Those counts come from each bag's published set yield — an 80 lb bag of QUIKRETE Concrete Mix yields about 0.60 cubic feet, a 60 lb bag about 0.45. Because you need dozens of bags per yard, ready-mix delivery is usually cheaper and faster once a job passes roughly one cubic yard.
How many cubic yards of concrete do I need?
Cubic yards = length × width × thickness ÷ 27, with every dimension in feet (divide inches by 12 first). For a footing or column, use the cross-section area times the length or height. The shortcut for a slab is area in square feet × thickness in inches ÷ 324. Add 5 to 10 percent for waste and order to the next quarter yard, since ready-mix plants sell in quarter-yard increments. The calculator above does all of this and shows cubic yards, cubic feet, and cubic meters at once.
How much does a yard of concrete weigh?
A cubic yard of normal-weight concrete weighs about 4,050 pounds, or just over 2 tons, based on a standard density of 150 pounds per cubic foot (27 ft³ × 150). Wet concrete is a little heavier than cured. This weight matters for subgrade and formwork, and it's why concrete is delivered by truck rather than carried — one full yard is more than most trailers should haul.
Should I use bagged concrete or ready-mix?
Bags make sense for small jobs — posts, small pads, and repairs up to roughly half a cubic yard. Past about 1 cubic yard (45 eighty-pound bags), ready-mix delivery is usually cheaper per yard, far less labor, and gives a single consistent pour with no cold joints between batches. The crossover depends on local delivery and short-load fees, so price both once your estimate is near a yard. The calculator gives you the bag count and the yardage side by side so you can compare.
How much concrete do I need for a driveway?
A concrete driveway is a slab 4 to 6 inches thick — 4 inches for cars, 5 to 6 inches with rebar for heavier vehicles. A single-car drive of about 12 × 24 ft at 5 inches needs roughly 4.4 cubic yards; a two-car drive near 20 × 24 ft at 5 inches needs about 7.4 cubic yards. Enter your dimensions and set the thickness with the Driveway preset above. Because these volumes are well past a yard, they're ready-mix jobs, not bag jobs.
How much concrete do I need to set a fence post?
For a post in a round hole, concrete volume is the hole volume minus the post. A common 4-inch post in a 10-inch-wide hole 24 inches deep needs about 0.9 cubic feet, or roughly two 60-pound bags, per hole. Rules of thumb: use a hole about three times the post width and one-third to one-half the above-ground post height deep. To estimate a batch of identical footings here, pick the circle shape, enter the hole diameter, set thickness to the hole depth, and set the quantity to your number of posts.
How much concrete do I need for round columns or tubes?
A column or form tube (such as a Sonotube) is a cylinder: volume = π × radius² × height. A 12-inch-diameter tube 4 feet tall holds about 3.1 cubic feet, or roughly 0.12 cubic yards — about five 80-pound bags. In the calculator above, choose the circle shape, enter the tube diameter, and set the thickness field to the pour height (switch its unit to feet). Use the quantity field to multiply across several identical piers in one estimate.
How much extra concrete should I order for waste?
Add 5 to 10 percent to the calculated volume. Ready-mix pours lose a little to spillage, uneven subgrade, and slightly over-thick spots; hand-mixed bag work loses a bit more, so lean toward 10 percent there. Running short mid-pour is far worse than a small surplus, because a second delivery or a fresh batch of bags creates a cold joint. The overage field above applies this allowance, and ready-mix is then rounded up to the next quarter yard.
How much does concrete cost?
As of 2026, ready-mix concrete runs roughly $140 to $180 per cubic yard for the material, before delivery, short-load fees, and labor. Bagged mix is about $5 to $8 for an 80-pound bag, which works out far higher per yard — one reason bags suit only small jobs. A finished slab, with forming, reinforcement, placing, and finishing, typically costs $6 to $12 per square foot installed. Enter your local price per yard or per bag above to turn the volume into a material total, and treat these ranges as a starting point to confirm locally.
Related calculators
Sources
- Concrete Mix No. 1101 — Product Data and YieldQUIKRETEPublished set yields per bag (40/50/60/80 lb) used for the bag-count table; these apply to this specific product.
- Concrete Basics and Slab-on-Ground GuidancePortland Cement Association (PCA)Basis for the ~150 lb/ft³ normal-weight concrete density (≈4,050 lb per cubic yard) and the residential slab thickness presets (4" typical; 5–6" under vehicle loads).
- NIST SP 811 — Guide for the Use of the International System of Units (SI)National Institute of Standards and Technology (NIST)Exact foot-to-metre conversion (1 ft = 0.3048 m) used for the cubic-meter output.
- How Much Does Concrete Cost Per Yard?HomeGuideNational 2025–2026 price ranges for ready-mix (per yard) and bagged mix used in the cost FAQ; regional rates vary.