How Many Bags of Concrete Per Cubic Yard?

The short answer

One cubic yard of concrete equals 27 cubic feet. Divide 27 by the yield of a single bag and you get the count per yard. Here it is in one table, using manufacturer bag yields:

These numbers are the planning baseline — the 45/60/90 rule of thumb (45 bags of 80 lb, 60 of 60 lb, 90 of 40 lb) covers the mixes most people buy.

How the math works

A bag's yield is the volume of finished concrete it produces, which is much less than the volume of dry mix in the bag — mixing and compaction shrink it. Take the 27 cubic feet in a yard and divide by the bag's yield. For an 80 lb bag yielding 0.60 cubic feet: 27 / 0.60 = 45 bags. The formula works for any bag size: bags per yard = 27 ÷ yield in cubic feet. Real yields vary slightly by mix design and how wet you batch, so treat these as verified-but-rounded figures and always round your order up.

Worked example: a 10×10 slab at 4 inches

Volume first: 10 × 10 × 0.333 = 33.3 cubic feet, ÷ 27 = 1.23 cubic yards. In 80 lb bags: 1.23 × 45 = 55.5 — round up to 56 bags. Add 10% overage and you're at 62 bags. That's a lot of lifting: at roughly 60 bags an hour of mixing work, a 10×10 slab is about the size where ready-mix starts looking very attractive.

Bag counts by common project

Most people don't buy “a cubic yard of bags” — they buy for a project. Same math, pre-computed, using 80 lb bags (yield 0.60 cu ft per bag). The “order” column adds 10% overage and rounds up:

A fence post is the classic small job: a 10-inch hole 30 inches deep needs about 2 bags of 80 lb mix after the post itself displaces its share — grab a third bag and you have margin for an uneven hole. A 12×12 slab is where the bag route starts to hurt: 80+ bags is two tons of lifting, which is exactly what the bagged vs ready-mix guide helps you decide.

Bag counts for the five most common slab sizes

Slabs are what most people actually buy bags for, so here is the same math pre-computed for the five slab sizes homeowners pour most — an 8×8 patio, a 10×10 shed pad, a 10×12 small patio, a 12×12 patio, and a 20×20 garage floor — at the two standard residential thicknesses, 4 and 6 inches. Convention used in both tables: cubic yards = length × width × (thickness in feet) ÷ 27; then Net bags = round up(yards × 45) for 80 lb bags (0.60 cu ft yield), and Order = round up(Net × 1.10) — a 10% waste buffer for spillage, uneven forms, and subgrade. Every figure below is built from the concrete calculator site's manufacturer-yield constants.

Four inches is the standard for patios, walkways, and shed pads — anything carrying people and light furniture. Step up to 6 inches for driveways, garage floors, and anything with vehicle weight or heavy equipment. If your slab is an odd size or a different thickness, the concrete calculator runs the same formula instantly. Two planning notes: most slabs sit on about 4 inches of compacted base — see how much gravel under a concrete slab to size it — and if your site needs regrading or fill before the slab, the dirt calculator estimates that volume so you're not pouring concrete into a low spot.

The ~1-yard breakeven rule

The materials math alone settles this: at $6 per 80 lb bag, one cubic yard via bags costs 45 × $6 = $270 in materials— before a single hour of mixing — while ready-mix typically runs $125–$195 per yard delivered. On price alone, bags lose at well under a yard. What keeps bags winning below ~1 yard is everything else: ready-mix short-load fees ($50–$200) and plant minimums punish tiny orders, while a couple of bags and a wheelbarrow don't.

At about 1 cubic yard the balance flips for good. A 10×12 slab at 4 inches is 1.48 yards — 74 bags to order, haul, and mix, roughly three tons of bag weight through your arms — versus one truck in twenty minutes. Beyond the breakeven, every extra bag is money and sweat you didn't need to spend. If the project is at or past this size and you're thinking about hiring it out instead, get a pro quote to see what a contractor would charge for your slab. The full bags-vs-delivery decision, including when the short-load fee flips back in bags' favor, is in the bagged vs ready-mix guide.

Bags vs ready-mix: the breakpoint

Bags make sense for small, irregular pours — fence posts, small pads, repairs — where the ready-mix minimum and short-load fee would punish you. But once you're past roughly 1 to 2 cubic yards, ready-mix delivery is usually cheaper per yard and you skip hours of mixing and hauling. A 10×20 driveway at 4 inches (2.47 yards) is 112 bags of 80 lb mix — over 4.5 tons of bags to move, versus one truck in 20 minutes. Watch for short-load fees ($50–$200) on small ready-mix orders under about 4 yards; for tiny pours, bags still win.

The real cost math

Ready-mix typically runs $125–$195 per cubic yard delivered (2026, region-dependent). Compare that against the bag route: bags-per-yard × price per bag + your time. At $6 per 80 lb bag, 45 bags costs $270 in materials alone — before you count the hours of mixing. The breakeven usually lands well under 2 yards. Above the breakeven, every extra bag is money and sweat you didn't need to spend.

Common mistakes

Forgetting the overage. Forms leak and subgrade is never perfectly level — 10% extra is the industry standard. Using the dry-mix volume. A bag's cubic-footage on the shelf isn't its yield; always use the finished-concrete yield. Ordering bags for a big pour. Above ~2 yards, the bag route is the most expensive and slowest way to move concrete. Mixing inches and feet. Convert thickness to feet first — 4 inches is 0.333 feet, not 4.