ConstructionCalc
Field referenceUpdated May 2026Material live from FREDYields QuikreteAnchor NRMCA 2024

Bagged concrete

Concrete Bag Calculator: How Many Bags Do You Need? + Cost

Tell us your project — we'll show the bag count for all four sizes (40/50/60/80 lb), the bagged total at your store price, and a hedged comparison against live ready-mix for slabs, round slabs, footings, and post-holes.

All 4 sizes · 40/50/60/80 lbLive ready-mix comparisonBag price editable4 small-project shapesImperial + Metric

Here's the deal

Buying bags at the store and not sure how many to grab? Punch in your dimensions, choose the size your store stocks, and you'll walk away with a count for all four sizes plus an honest read on whether ready-mix would be cheaper — no fake crossover number, just the math and the range. We've got this.

Buying bags for:

A patio slab?A shed pad?A fence post?A small footing?A round pad?
A 10 × 10 ft slab at 4 inches needs 62 eighty-pound bags (or 82 × 60 lb, 98 × 50 lb, 123 × 40 lb). At a $6.50/bag default for 80 lb that's about $403. For ~1.4 yd³ it's close — see the live breakeven below.

The bag count is exact geometry: the order volume (your dimensions plus 10% for waste) divided by each bag's yield, rounded up. Bag prices are sourced retail estimates and editable — override the default with your local store price for an exact total. The ready-mix side is live: material is escalated monthly from the BLS ready-mix PPI, and the short-load fee is presented as a range, because small-order delivery pricing varies widely.

LENGTHWIDTHTHICKNESSlength × width × thickness = concrete

Rectangular slab — length × width × thickness.

= 3.05 m
= 3.05 m
= 10.2 cm
Sourced default — volatile retail; override with your store price for an exact total.

Enter your measurements,
then hit Calculate

Your full breakdown — yards, tons, bags, loads and cost — appears here.

Step 1

Which shape are you bagging?

Pick the shape that matches your project and measure what the diagram calls out. The calculator returns the bag count for all four sizes at once — you choose which to buy at the store.

LENGTHWIDTHTHICKNESSlength × width × thickness = concrete
Slab
L × W × thickness

Patios, shed pads, walkways — the most common bag project. Counts come back for all four sizes.

DIAMETERTHICKNESSπ × (diameter ÷ 2)² × thickness = concrete
Round slab
π × (D ÷ 2)² × thickness

Round pads and bases under tanks or columns. The calculator returns all four bag-size counts.

LENGTHWIDTHDEPTHlength × width × depth = concrete
Footing
L × W × depth

Small piers and short footing runs. Long runs cross into ready-mix; bag counts shown for every size.

DIAMETERHEIGHT× Nn × π × (diameter ÷ 2)² × height = concrete
Post-hole / column
n × π × (D ÷ 2)² × H

Fence posts, deck footings, mailbox posts. Enter the hole and count — all four bag sizes returned.

Captions stay bags-first because that's why you're here. Wall and stairs aren't in this set — both are ready-mix territory past any bag-economic crossover, and live on the concrete calculator instead, alongside the full bag-yield reference table.

Worked examples

Four small projects, with the bag count

Each shows the order volume (geometry + 10% waste) and the 80-pound bag count; the calculator also gives 40/50/60-pound counts at the same time. These four span the full range where bagged concrete is the realistic choice — from a single fence post you can dig in an afternoon to a small slab on the edge of needing ready-mix.

Fence post10-inch hole, 2 feet deep, one post

π × (10/12 ÷ 2)² × 2 = 1.09 ft³ · +10% waste → order 1.20 ft³
2 × 80-lb bags (standard concrete mix)

A 10-inch-wide hole 2 feet deep holds about 1.2 cubic feet with waste, which is 2 eighty-pound bags of standard concrete mix. A 4×4 post sits in that hole and displaces a little concrete, so you may use slightly less — within the waste buffer. For multiple posts, enter the count and the calculator multiplies.

Shed pad4 × 4 ft at 4 inches

4 × 4 × (4 ÷ 12) = 5.33 ft³ · +10% waste → order 5.87 ft³
10 × 80-lb bags

That is about 5.9 cubic feet with waste, or 10 eighty-pound bags. A pad this small is squarely bag territory — far below any ready-mix minimum.

Slab10 × 10 ft at 4 inches

10 × 10 × (4 ÷ 12) = 33.33 ft³ · +10% waste → order 36.67 ft³ (~1.4 yd³)
62 × 80-lb (or 82 × 60 lb, 98 × 50 lb, 123 × 40 lb)

About 36.7 cubic feet with waste: 62 eighty-pound bags (or 82 × 60 lb, 98 × 50 lb, 123 × 40 lb). At roughly 1.4 cubic yards this is where the bags-versus-ready-mix question starts to matter — see the breakeven below.

Small footing10 ft run, 12 inches wide, 12 inches deep

10 × 1 × 1 = 10.0 ft³ · +10% waste → order 11.0 ft³
19 × 80-lb bags

About 11 cubic feet with waste, or 19 eighty-pound bags. Still well under the ready-mix minimum, so bagging is practical.

Bags per cubic yard

How many bags make a cubic yard?

Bag count comes from the order volume divided by each bag's yield, always rounded up to whole bags. A cubic yard is 27 cubic feet — and that works out to:

45
80 LB BAGS / YD³
0.60 ft³ each · economical default
60
60 LB BAGS / YD³
0.45 ft³ each
72
50 LB BAGS / YD³
0.375 ft³ each
90
40 LB BAGS / YD³
0.30 ft³ each · easiest to carry solo

The 80-pound bag is the most economical per cubic foot, which is why it's the default and the size most contractors reach for. Lighter bags cost more per cubic foot but are easier to carry and mix solo — a real consideration if you're working alone or moving bags up steps to the pour site.

Round up, always. A partial bag means a partial pour, so buying five 80-pound bags when geometry says 4.2 is the difference between finishing the pour and stopping mid-finish to drive to the store. Far cheaper to carry one extra bag home than to leave a cold joint in the slab.

All four sizes are the same mix, so you can combine them in one pour as long as each batch keeps the same water ratio. For the full yield, coverage, and bags-per-yard reference table, see the concrete calculator.

The honest math

Bags or ready-mix? The honest breakeven

The usual advice — “bags under a yard, ready-mix above” — is roughly right but misses why, and the why changes your decision.

It isn't the per-yard price

Bagged concrete works out to about $290–340 per cubic yard all-in; ready-mix material is around $184 per cubic yard at current rates. On the per-yard rate alone, ready-mix wins almost immediately — so why do bags win small jobs?

It's the minimum-order reality

A ready-mix truck costs the same to send whether it carries one yard or ten, so suppliers protect that fixed cost with a short-load fee and an order minimum. The fee varies a lot — roughly $40–100 per cubic yard for orders under about 10 yards, and some plants charge a flat per-delivery penalty instead. Many won’t economically deliver under about 4–5 yards.

So the crossover is a zone, not a line

Below about 1 cubic yard, bags almost always win — not because the concrete is cheaper, but because small-load fees, minimums, and scheduling a truck for a tiny pour make bagging the practical choice. Above about 1.5–2 cubic yards (roughly 68–90 eighty-pound bags), ready-mix pulls clearly ahead on both price and labor. In between, it genuinely depends on your supplier’s fees.
One more option for tiny jobs:volumetric or “metered” delivery (and trailer-mounted self-delivery) lets you pay only for what you use with no short-load fee, which can beat both bags and standard ready-mix for awkward small loads. Worth a call to local suppliers if your job is in the fuzzy zone.

The interactive verdict + the volume marker on the crossover scale live in the calculator above. The verdict is tiered honestly: bags clearly cheaper, ready-mix clearly cheaper, or it's close — get two quotes, with bags as the practical choice whenever your job is under about one cubic yard regardless of price math.

We chose the hedged tiering on purpose. A single crossover number — like “1.7 yd³ is the breakeven” — would be false precision because the dominant cost on small ready-mix orders is the truck's fixed dispatch cost, which suppliers recover differently from each other. Your local plant's minimum order and flat short-load policy matters more than any rate we can publish, which is why the section above tells you to call.

What bags cost

How much do concrete bags cost?

Retail bag prices move with the market and vary by store, so the calculator uses an editable price field — check your store's shelf price and type it in. As sourced starting points:

~$6.50
80 LB BAG
~$293/yd³
~$5.00
60 LB BAG
~$300/yd³
~$3.75
40 LB BAG
~$338/yd³

Per cubic yard of finished concrete those work out to roughly $293 (80 lb), $300 (60 lb), and $338 (40 lb) — confirming the 80-pound bag as the cheapest way to buy bagged concrete.

The 50-pound bag's price isn't from a source we'll vouch for, so the calculator leaves that field blank for you to fill. Bag count for the 50 lb size is unaffected — counts are exact geometry.

Bag prices are volatile retail figures that swing with seasonal demand and regional fuel costs more than concrete prices do. We ship sourced defaults so the calculator gives a useful number out of the box, but override them with your store's shelf price for a real total — the calculator is designed around the edit, not around the default. The same applies to the bag size: switch sizes in the dropdown and the price field auto-fills to that size's sourced default (and clears for 50 lb).

Before you mix

Tips for bagging

Keep the water ratio consistent

Mixing bag to bag with the same water gives even strength and color; eyeballing it weakens the pour. Combine sizes freely as long as the ratio holds.

Buy one extra bag

Rounding up is already built in, but a spare bag on site beats a second trip mid-pour — a partial bag is far cheaper than a cold joint.

Fence posts often use fast-setting mix

The calculator computes standard concrete mix; fast-setting products (the kind you can pour dry into the hole) have their own yield printed on the bag, so check it if that is what you are using.

Questions

Concrete bag calculator FAQ

How many bags of concrete do I need for a 10 × 10 slab?
A 10 × 10 ft slab at 4 inches needs about 62 eighty-pound bags (82 × 60 lb, 98 × 50 lb, or 123 × 40 lb), including 10% for waste. At 6 inches it is about half again as many; enter your thickness for the exact count.
How many bags of concrete are in a cubic yard?
It takes 45 eighty-pound bags, 60 sixty-pound bags, 72 fifty-pound bags, or 90 forty-pound bags to make one cubic yard. The 80-pound bag is the most economical per cubic foot.
How many bags of concrete for a fence post?
About 2 eighty-pound bags for a typical 4×4 post in a 10-inch hole 2 feet deep, with standard concrete mix. The post displaces a little, so you may use slightly less; fast-setting mixes have a different yield printed on the bag.
What size concrete bag is cheapest?
The 80-pound bag, at roughly $293 per cubic yard of finished concrete versus about $300 (60 lb) and $338 (40 lb). Lighter bags cost more per cubic foot but are easier to handle alone.
When should I switch from bags to ready-mix?
Above about 1.5 to 2 cubic yards — roughly 68 to 90 eighty-pound bags. Below about 1 cubic yard, bags almost always win once you count ready-mix short-load fees and minimums.
Can I mix different bag sizes in one pour?
Yes — all four sizes are the same mix, so combining them is fine as long as each batch keeps the same water-to-mix ratio. The calculator gives the count for every size so you can mix and match.
How much does a bag of concrete cost?
About $6.50 for an 80-pound bag, $5.00 for 60-pound, and $3.75 for 40-pound as sourced starting points, but retail prices vary by store and season. The calculator lets you enter your store’s actual price.
Do I subtract the post when calculating concrete for a post hole?
For precision, yes — the concrete fills the hole minus the post, so a 4×4 in a 10-inch hole uses a little less than the full hole volume. For a standard post that difference is small and falls within the waste allowance, so the calculator’s hole-based count is a safe order.

Receipts

Sources & methodology

Pinned sources

Tool-specific choices behind these numbers

Bag counts are exact geometry
Volume ÷ yield, rounded up. The yields are the manufacturer’s published values (QUIKRETE Concrete Mix Model 110180, corroborated by Cemex) — 0.30, 0.375, 0.45, 0.60 ft³ for the 40/50/60/80 lb sizes. We don’t estimate them, and we never round bags down: a partial bag means a partial pour.
Bag prices are yours to set
Retail bag prices are volatile and store-specific, so we ship sourced defaults you can overwrite rather than freezing a number that goes stale. The 80/60/40 lb defaults come from CalcShed per-yard equivalents; check your store’s shelf price and type it in for an exact total.
No 50-pound default price
We have a verified per-yard figure for the 40, 60, and 80 lb sizes; we do not for 50 lb. Rather than interpolate or paraphrase a competitor, we leave the 50 lb price field blank — verified or omitted. The 50 lb bag count is fine because that is exact geometry.
Ready-mix is live; the short-load fee is a range
Material escalates monthly from BLS series PCU327320327320 via the FRED API, anchored to the NRMCA 2024 average of $179.89/yd³ paired to that year’s annual-average index of 390.90. The short-load fee genuinely varies 5× by supplier and is often charged flat rather than per-yard, so we present it as a $40–100/yd³ range and never a single quoted fact.
Why the breakeven is a zone
A truck’s fixed cost — not the per-yard rate — drives the small-job math, and that cost is recovered through minimums and flat fees that differ by plant. A precise crossover yard would be false precision, so we give a hedged verdict and a guidance zone (~1 yd³ to ~2 yd³) and tell you to get two quotes inside that zone.
Standard mix, not fast-setting
Counts assume standard concrete mix at the manufacturer-published yields. Fast-setting products (the kind you can pour dry into a post hole) have their own yield printed on the bag, which we flag rather than guess. If you are using a fast-setting product, use the printed yield instead of ours.

For the shared principles — the “real ≠ right” rule, the primary-source standard, and the publish-our-receipts stance behind every figure on the site — see the methodology page.

Spot a number that looks off? Email info@constructioncalc.org with the page URL and what you saw — we publish a fix as soon as the underlying source can be confirmed.
RelatedConcrete calculator (full volume)All six shapes — slabs, footings, columns, walls, stairs — plus the bag-yield reference table.RelatedConcrete slab cost calculatorInstalled cost per square foot, material live from FRED, labor as a typical regional range.RelatedMethodologyHow every number on the site is sourced and computed.