Bags of Concrete Calculator
This free bags of concrete calculator answers the most common concrete question there is: how many bags do I need? Enter what you're pouring — a slab or pad, a footing, or round post holes — choose your bag size, and it returns the whole-bag count with a waste allowance already added. Under the hood it uses the manufacturer-published yields: a 60 lb bag makes about 0.45 cubic feet, an 80 lb bag about 0.60, so it takes 60 bags of 60 lb or 45 bags of 80 lb to fill one cubic yard.
It also works as a two-way converter. Flip to converter mode to turn any volume into bags of every size side by side ("how many 80 lb bags in 1.5 yards?"), or turn a bag count back into cubic feet and yards. A yield chart on the page lists every standard bag — 40, 50, 60, and 80 lb — with its cubic-foot yield and bags-per-cubic-yard, so the numbers are there even before you calculate.
Because bagged concrete only makes sense up to a point, the calculator flags when you've crossed into ready-mix territory — around two to three cubic yards, where hand-mixing that many bags becomes a full day of labor. Quantities and mixing guidance only — no pricing, no signup. For a full project take-off with rebar and base, use the Concrete Calculator.
Bags of Concrete Calculator
Find how many 40, 50, 60, or 80 lb bags of concrete you need for a slab, footing, or post holes — or convert between bags and cubic yards. Free, no signup.
What do you want to do?
Your pour
Slab thickness minimums: 3.5" is the IRC code minimum, 4" is standard for patios, sidewalks, and garage floors; use 6" for driveways with heavy vehicles.
Bag & waste
10% waste covers spillage and uneven subgrade on a typical job; bump to 15% for rough forms or lots of small pours. Bags are always rounded up to a whole bag.
Concrete bag yield chart
How much each standard bag of concrete yields, and how many it takes to make a cubic yard. Yields are manufacturer-published (Quikrete #1101, Sakrete High-Strength); cubic-yard and bags-per-yard figures are derived (1 yd³ = 27 ft³).
| Bag size | Yield (ft³) | Yield (yd³) | Bags per cubic yard |
|---|---|---|---|
| 40 lb | 0.3 ft³ | 0.011 yd³ | 90 bags |
| 50 lb | 0.375 ft³ | 0.014 yd³ | 72 bags |
| 60 lb | 0.45 ft³ | 0.017 yd³ | 60 bags |
| 80 lb | 0.6 ft³ | 0.022 yd³ | 45 bags |
| 90 lb (regional) | 0.66 ft³ | 0.024 yd³ | 41 bags |
90 lb is a regional size; 66 lb (30 kg) is Canada-only and not shown. Yields are stated by manufacturers as "approximate" and vary with water content, compaction, and spillage.
Concrete bag yields at a glance
Every bag count comes down to one number — how many cubic feet a bag of concrete makes — and one constant: a cubic yard is 27 cubic feet. These two diagrams show the whole relationship so the math behind the calculator is easy to sanity-check.
The bigger the bag, the more concrete it makes, so the fewer you need. Bar height here is each bag's yield in cubic feet — a 40 lb bag makes about 0.30, an 80 lb bag about 0.60, twice as much — and the count below each bar is how many it takes to fill one cubic yard (27 divided by the yield).
Working the conversion the other way answers the most-searched version of the question: one cubic yard is 27 cubic feet, so it takes 45 bags of 80 lb (0.60 ft³ each) or 60 bags of 60 lb (0.45 ft³ each). The gauge is the practical part — past about half a cubic yard, roughly 25 eighty-pound bags, hand-mixing stops being worth it and a ready-mix truck wins.
Calculation Formulas
Convert thickness from inches to feet, then multiply the three dimensions for cubic feet. This is the volume the bags have to fill.
Example:
A 10 ft × 10 ft pad at 4" thick = 10 × 10 × (4 ÷ 12) = 33.3 ft³.
Footings are entered with a length in feet and a cross-section in inches. Both cross-section dimensions convert to feet before multiplying.
Example:
A 20 ft footing, 12" wide × 12" deep = 20 × 1 × 1 = 20 ft³.
A hole is a cylinder: radius is half the diameter (÷ 24 converts a diameter in inches straight to a radius in feet), squared, times π, times depth. Multiply by the number of holes. The post itself is not subtracted, so you buy a little extra.
Example:
One 12"-dia × 36"-deep hole = π × (0.5 ft)² × 3 ft = 2.36 ft³.
One cubic yard is 27 cubic feet. This is the number that decides whether bags or a ready-mix truck makes more sense.
Example:
33.3 ft³ ÷ 27 = 1.23 yd³.
Divide the volume by the per-bag yield and round up to a whole bag. Yield is fixed per bag size (a 60 lb bag ≈ 0.45 ft³, an 80 lb bag ≈ 0.60 ft³).
Example:
33.3 ft³ ÷ 0.60 ft³ (80 lb) = 55.5 → 56 bags before waste.
Apply the waste factor to the volume, then divide by yield and round up. 10% is the standard allowance for spillage and uneven subgrade.
Example:
33.3 ft³ × 1.10 ÷ 0.60 = 61.1 → 62 bags of 80 lb with 10% waste.
Manufacturers publish a per-bag cubic-foot yield but do NOT print a bags-per-yard figure — it is simply 27 divided by the yield. That gives the familiar 60 (60 lb) and 45 (80 lb) bags per yard.
Example:
27 ÷ 0.45 = 60 bags of 60 lb; 27 ÷ 0.60 = 45 bags of 80 lb.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| 40 lb Bag Yield | 0.30 ft³ (90 bags/yd³) | Quikrete #1101 / Sakrete published yield for a 40 lb bag of standard concrete mix. |
| 50 lb Bag Yield | 0.375 ft³ (72 bags/yd³) | 50 lb bag yield — the common size for fast-setting and 5000 mixes. |
| 60 lb Bag Yield | 0.45 ft³ (60 bags/yd³) | 60 lb bag yield. Quikrete and Sakrete publish identical figures at this weight. |
| 80 lb Bag Yield | 0.60 ft³ (45 bags/yd³) | 80 lb bag yield — the largest standard size and the most economical per cubic foot for larger pours. |
| 90 lb Bag Yield | 0.66 ft³ (41 bags/yd³) | Regional 90 lb bag (uses the conservative Sakrete figure; Quikrete lists 0.675). Not sold everywhere. |
| Cubic Yard | 27 ft³ | 1 cubic yard = 27 cubic feet — the conversion behind every bags-to-yards figure. |
| Waste Factor | 10% typical / 15% rough | 10% covers spillage and uneven subgrade on a normal job; 15% for rough forms or many small pours. Bags always round up to a whole bag. |
| Bag-vs-Ready-Mix Crossover | ~2–3 yd³ | Above roughly two to three cubic yards, hand-mixing bags becomes a full day of labor and ready-mix delivery is usually the better call. |
| Mixing Water | ~6 pt / 80 lb, 4–7 pt / 60 lb | Starting water per bag. Exceeding the max (≈9 pt for 80 lb) sharply cuts strength — one extra quart can drop an 80 lb bag from 4000 to 2500 PSI. |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
ASTM C387 — Packaged, Dry, Combined Materials for Mortar and Concrete(ASTM C387/C387M)
View StandardThe product specification governing bagged concrete mix — the packaged, dry, pre-combined cement and aggregate you buy by the bag. Sets the strength and performance requirements manufacturers design their mixes to meet.
Key Requirements:
- •Standard packaged concrete mix reaches ~2,500 PSI at 7 days and ~4,000 PSI at 28 days
- •High-early / 5000 mixes reach ~5,000 PSI at 28 days
- •Water added per the bag label; exceeding the maximum reduces compressive strength
- •Yield stated by weight of packaged material (a 60 lb bag ≈ 0.45 ft³)
Manufacturer Technical Data Sheets — Bag Yields(Quikrete #1101 / Sakrete TDS)
View StandardPer-bag yield figures come directly from manufacturer data sheets. Quikrete and Sakrete publish identical yields for standard and high-strength concrete at each bag weight, and both qualify them as 'approximate.'
Key Requirements:
- •40 lb ≈ 0.30 ft³ · 50 lb ≈ 0.375 ft³ · 60 lb ≈ 0.45 ft³ · 80 lb ≈ 0.60 ft³
- •Yield tracks bag weight, not formulation — fast-setting and standard yield the same
- •No 80 lb fast-setting bag exists; fast-setting is sold in 50 and 60 lb only
- •Manufacturers publish ft³ yield only — bags-per-cubic-yard is a derived figure
IRC R506 — Concrete Slabs-on-Ground(IRC R506.1)
View StandardThe residential code minimums for interior and exterior slabs-on-grade, which set the thickness the calculator's slab mode is estimating for.
Key Requirements:
- •Minimum 3.5" slab thickness; 4" is the common standard for patios and garage floors
- •Slab placed over a prepared base course with a vapor retarder where required
- •6" thickness typical for driveways carrying heavy vehicles
IRC R403 — Footings(IRC R403.1)
View StandardPrescriptive minimum footing dimensions, relevant to the footing mode and to bag counts for small pier and footing pours.
Key Requirements:
- •Minimum 12" width and 12" depth below undisturbed ground as a baseline
- •Footings extend below the local frost line
- •Minimum 2,500 PSI concrete for footings and foundations
ACI 306 — Cold Weather Concreting(ACI 306R)
View StandardGoverns placing concrete in cold weather, which affects whether a fast-setting or high-early bag is the right choice for a given pour.
Key Requirements:
- •Cold-weather procedures apply below 40°F
- •Concrete must reach ~500 PSI before freezing
- •Fast-setting and high-early mixes help hit strength before a freeze
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Bag Sizes Available by Region
Not every size is stocked everywhere
40, 50, 60, and 80 lb are the standard US sizes. The 90 lb bag is regional, and the 66 lb (30 kg) and 55 lb bags are Canada-only metric packs — a US calculator hides them by default.
Regional Examples:
Fast-Setting for Posts
Poured dry into the hole
For fence, deck, and mailbox posts, fast-setting concrete is poured dry into the hole and water is added on top — no mixing. It sets in 20–40 minutes. It is sold in 50 and 60 lb bags only; there is no 80 lb fast-setting bag.
Regional Examples:
Cold-Weather & High-Early Mixes
Getting to strength before a freeze
In cold climates, high-early-strength (5000) mixes reach usable strength faster, reducing the risk of freeze damage before the concrete cures. Cold-weather placement (below 40°F) also calls for protecting the pour.
Regional Examples:
Bag vs. Ready-Mix Crossover
When to stop bagging
Small pours are cheaper and simpler with bags; large pours are faster and more consistent with a ready-mix truck. The practical crossover is around two to three cubic yards, where hand-mixing becomes a full day of labor.
Regional Examples:
Waste & Field Verification
Always buy a little extra
Spillage, uneven subgrade, and over-excavated holes all consume more concrete than the clean geometry suggests. A 10% allowance covers a typical job; rough forms and many small pours warrant 15%.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
Heavy material — watch the weight limit
Concrete, brick, and masonry hit tonnage caps fast. Most dumpsters cap heavy material at 10 tons, and overage fees stack quickly. See the disposal guide before you load.
Read the heavy-debris guide →
Related Calculators
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How to Use This Calculator
- Choose a mode: estimate bags from a project, or use the bags ↔ cubic-yards converter.
- In project mode, pick what you're pouring — slab/pad, footing, round post holes, or a known volume — and enter the dimensions.
- Select your bag size (40, 50, 60, or 80 lb; toggle on the regional 90 lb if your store carries it) and mix type.
- Set a waste factor (10% for a normal job, 15% for rough forms or many small pours), then click Calculate.
- Read the bag count (with and without waste), the volume in cubic feet and yards, and the bag-vs-ready-mix guidance.
- Use converter mode to answer questions like "how many 60 lb bags in a cubic yard?" — it shows every bag size at once.
How Many Bags of Concrete Make a Cubic Yard?
One cubic yard is 27 cubic feet. Since a 60 lb bag of concrete yields about 0.45 cubic feet and an 80 lb bag yields about 0.60, it takes 60 bags of 60 lb or 45 bags of 80 lb to make a full cubic yard (40 lb → 90 bags, 50 lb → 72 bags). Manufacturers publish only the per-bag cubic-foot yield — the bags-per-yard number is simply 27 divided by that yield, which is why you'll see it stated as "approximately." Those yields track bag weight, not the mix: fast-setting and standard concrete yield the same at the same bag weight. Once a job needs more than roughly two to three cubic yards, the bag count gets large enough that hand-mixing is a full day of work and ready-mix delivery usually wins — this calculator points that out when you cross the line.
Frequently Asked Questions
How many bags of concrete do I need?
Work out the volume in cubic feet, then divide by the bag's yield and round up. A 60 lb bag yields about 0.45 ft³ and an 80 lb bag about 0.60 ft³. Worked example: a 10 ft × 10 ft slab at 4" thick is 10 × 10 × (4 ÷ 12) = 33.3 ft³; at 0.60 ft³ per 80 lb bag that's 56 bags before waste, or about 62 bags with a 10% allowance. This calculator does that for a slab, footing, or post holes and adds the waste for you.
How many bags of concrete make a cubic yard?
One cubic yard is 27 cubic feet, so the count depends on bag size: 60 bags of 60 lb, 45 bags of 80 lb, 72 bags of 50 lb, or 90 bags of 40 lb. Manufacturers publish only the per-bag cubic-foot yield (60 lb ≈ 0.45 ft³, 80 lb ≈ 0.60 ft³); the bags-per-yard figure is just 27 divided by that yield, which is why it's always stated as 'approximately.'
How many cubic feet are in a 60 lb or 80 lb bag of concrete?
A 60 lb bag of concrete yields approximately 0.45 cubic feet (0.017 cubic yards), and an 80 lb bag yields approximately 0.60 cubic feet (0.022 cubic yards). A 40 lb bag is about 0.30 ft³ and a 50 lb bag about 0.375 ft³. Quikrete and Sakrete publish identical yields at each weight, and all are labeled 'approximate' because real yield varies with water content, compaction, and spillage.
Do fast-setting bags yield the same as standard concrete?
Yes. Yield tracks the weight of dry mix in the bag, not the chemistry, so a 50 lb fast-setting bag yields the same ~0.375 ft³ as a 50 lb standard bag. The difference is set time, not volume. One thing to note: fast-setting concrete is sold only in 50 and 60 lb bags — there is no 80 lb fast-setting bag from Quikrete, Sakrete, or Rapid Set.
How many bags of concrete for a fence post?
Size the hole first — depth about one-third of the above-ground post height, diameter about three times the post width (a 4×4 post → a 12" hole). A 12"-diameter, 36"-deep hole is about 2.4 ft³, which is roughly 4 bags of 60 lb or 6 bags of 50 lb per hole (before subtracting the post itself, so you'll have a little extra). Fast-setting mix is popular here because you pour it dry into the hole and add water — no mixing. Use the post-hole mode to do all your holes at once.
When should I use bags vs. ready-mix concrete?
The practical crossover is around two to three cubic yards. Below about one cubic yard, bags mixed by hand or in a rented mixer are simpler and avoid ready-mix delivery minimums. Above two to three yards the bag count gets large and hand-mixing becomes a full day or more of labor, so a ready-mix truck is usually faster and more consistent. This calculator flags which side of the line you're on; for a full truck-order take-off, use the Concrete Calculator.
What waste factor should I add for bagged concrete?
Ten percent covers spillage, uneven subgrade, and over-excavated holes on a typical job. Bump it to 15% for rough forms or a lot of small pours. Because bags are sold whole, the calculator always rounds up — and it's worth keeping one spare bag on hand, since running short in the middle of a pour creates a cold joint you can't undo.