Calculators / Concrete
Concrete Calculator
A 10 × 10 ft slab, 4 in thick, needs 1.23 cubic yards of concrete (33.3 cu ft). With 10% extra, plan on 1.36 cubic yards: 62 bags of 80-lb mix or 82 bags of 60-lb mix. Enter your size below.
How much concrete do you need?
1.04 m³, including 10% extra.
| Bag size | Bags | Total weight |
|---|---|---|
| 80 lb (0.60 cu ft each) | 62 | 4,960 lb |
| 60 lb (0.45 cu ft each) | 82 | 4,920 lb |
| 40 lb (0.30 cu ft each) | 123 | 4,920 lb |
What it costs
| Ready-mix, 1.50 cu yd delivered | $210-$293 |
|---|---|
| 82 bags of 60-lb mix at $4.85 | $398 |
Ready-mix at $140 to $195 per cubic yard, rounded up to the next quarter yard, plus a short-load fee of $75 to $250 on small orders. Bag price from Menards on October 24, 2026. Prices vary by area.
Over 1 cubic yard, ready-mix delivery is usually easier, and often cheaper than bags.
How much will it cost? Replacing a 600 sq ft concrete driveway, 4 in thick, typically costs $7,200 installed, including removal of the old one. Concrete driveway cost in your state
How to calculate concrete
Slabs, patios and footings: cubic feet = length (ft) × width (ft) × thickness (in) ÷ 12. Divide by 27 for cubic yards. Example: 10 ft × 10 ft × 4 in ÷ 12 = 33.3 cu ft, and 33.3 ÷ 27 = 1.23 cu yd.
Round columns and post holes: cubic feet = 3.1416 × (diameter in inches ÷ 24)² × depth (ft). For a post hole, subtract the post. Example: a 10 in hole, 3 ft deep, holds 1.64 cu ft; a 4x4 post takes up 0.26 cu ft of it, which leaves 1.38 cu ft of concrete.
Bags: cubic feet ÷ bag yield, rounded up. An 80-lb bag makes about 0.60 cu ft, a 60-lb bag 0.45 cu ft and a 40-lb bag 0.30 cu ft. Extra: add 5 to 10% for spills, uneven ground and forms that bow.
Concrete for common slab sizes
4 in thick, with 10% extra.
| Slab size | Cubic yards | 80-lb bags | 60-lb bags |
|---|---|---|---|
| 4 × 4 ft | 0.22 | 10 | 14 |
| 6 × 6 ft | 0.49 | 22 | 30 |
| 8 × 8 ft | 0.87 | 40 | 53 |
| 10 × 10 ft | 1.36 | 62 | 82 |
| 10 × 12 ft | 1.63 | 74 | 98 |
| 12 × 12 ft | 1.96 | 88 | 118 |
| 12 × 16 ft | 2.61 | 118 | 157 |
| 16 × 16 ft | 3.48 | 157 | 209 |
| 20 × 20 ft | 5.43 | 245 | 326 |
| 24 × 24 ft | 7.82 | 352 | 470 |
Concrete for fence posts
Per hole, with the post in place and 10% extra.
| Hole | Post | Cubic feet | 80-lb bags | 60-lb bags |
|---|---|---|---|---|
| 8 in wide, 2 ft deep | 4x4 | 0.58 | 1 | 2 |
| 10 in wide, 2 ft deep | 4x4 | 1.01 | 2 | 3 |
| 10 in wide, 3 ft deep | 4x4 | 1.52 | 3 | 4 |
| 12 in wide, 3 ft deep | 4x4 | 2.31 | 4 | 6 |
| 12 in wide, 3 ft deep | 6x6 | 1.90 | 4 | 5 |
| 12 in wide, 4 ft deep | 6x6 | 2.53 | 5 | 6 |
What concrete costs
Ready-mix concrete delivered by truck cost $140 to $195 per cubic yard in the 2025 and 2026 public supply contracts we reviewed, and small loads often add a short-load fee of $75 to $250. Bagged mix costs more per yard: at $4.85 per 60-lb bag, one cubic yard takes 60 bags, about $291 before tax. Pouring and finishing are extra if you hire it out: see concrete driveway cost for an installed price. Setting fence posts? See what fence installation costs.
Common questions
How many bags of concrete are in a yard?
One cubic yard (27 cu ft) takes 45 bags of 80-lb mix, 60 bags of 60-lb mix or 90 bags of 40-lb mix, before any extra.
How much concrete do I need for a 10x10 slab?
At 4 in thick, a 10 × 10 ft slab needs 1.23 cubic yards. With 10% extra, that is 62 bags of 80-lb mix or 82 bags of 60-lb mix. At 6 in thick, it needs 1.85 cubic yards.
How thick should a concrete slab be?
The residential building code sets 3.5 in as the minimum for concrete floors on the ground (International Residential Code R506.1). Patios, walkways and shed floors are usually poured 4 in thick. Driveways are usually 4 to 6 in, thicker where heavy vehicles park.
Should I buy 60-lb or 80-lb bags?
The mix is the same; only the bag size differs. An 80-lb bag makes 0.60 cu ft and a 60-lb bag 0.45 cu ft, so you need a third more 60-lb bags. 60-lb bags are easier to lift and to mix by hand.
How much concrete do I need for a fence post?
For a 10 in hole, 3 ft deep, with a 4x4 post, you need about 1.52 cu ft of concrete with 10% extra: 3 bags of 80-lb mix or 4 bags of 60-lb mix per post. See the table above for other hole sizes.
Bags or ready-mix: which is better?
Under about 1 cubic yard, bags are usually easier to buy and mix. Above that, ready-mix is often cheaper and saves a lot of work: one cubic yard is 60 bags of 60-lb mix, about $291 and 3,600 lb to lift and mix, versus $140 to $195 delivered plus any short-load fee.
How much does a yard of concrete weigh?
Standard concrete weighs about 145 to 150 lb per cubic foot, so a cubic yard weighs about 4,000 lb. The calculator also shows the total weight of the bags you need, which helps you plan the trips.
How we calculated this
Volumes use the standard geometry shown above. Bag yields come from the Quikrete Concrete Mix data sheet. Ready-mix prices come from public supply contracts, such as the City of Des Moines contract (April 2026), and the bag price from Menards (October 24, 2026). We test the calculator against 155 worked examples, checked with a separate program. Sources.
Results are estimates. Check your measurements, and ask your supplier how they round orders.
Changelog
- : Published.
- : Formulas checked against 155 worked examples, verified with a separate program.
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