ToolwickConcrete Bags Per Cubic Yard Calculator: How Many Bags of Concrete Per Yard?
This how many bags of concrete per yard calculator converts a slab size or a cubic-yard volume into the number of 40, 50, 60 or 80 lb bags you need to buy, with a waste allowance, total weight and optional cost.
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How to Use This Concrete Bags Per Cubic Yard Calculator
Pick "By slab size" and enter the length and width in feet and the thickness in inches, or pick "By cubic yards" if you already know the volume. Choose the bag size you plan to buy, set a waste allowance (10% is a sensible default), and press Calculate. You get the total bags to buy, the bags per cubic yard before waste, the total weight, a comparison of every bag size, and an optional cost estimate.
Why This Matters
Bagged concrete is priced per bag, but concrete volume is measured in cubic yards, and the two do not convert in your head. A 50 lb bag yields only about 0.375 cubic feet, so a single cubic yard takes 72 of them. If you are pouring a 10 × 10 ft patio at 4 inches thick, that is about 1.23 yards, or roughly 89 bags before waste. Underbuying is the expensive mistake: concrete starts setting within an hour or so, and a mid-pour trip to the store can leave a cold joint in the middle of your slab.
Homeowners use this for walkways, shed pads, steps, fence post footings and small repairs. Contractors use it to decide whether bags still make sense. As a rule, once a job passes one or two cubic yards, the labor of mixing 72 to 150 bags by hand and the weight of hauling roughly 3,600 to 7,200 lb of dry mix usually make ready-mix delivery a better choice. Knowing the exact count lets you compare both options with real numbers instead of guesses.
How It's Calculated
The calculator follows these steps, using the nominal yields printed on most major bag-mix labels:
Volume (cu ft) = length (ft) × width (ft) × thickness (in) ÷ 12
Cubic yards = cubic feet ÷ 27
Bags = cubic feet × (1 + waste %) ÷ yield per bag, rounded up
| Bag size | Yield (cu ft) | Bags per cubic yard | Dry weight per yard (lb) |
|---|---|---|---|
| 40 lb | 0.30 | 90 | 3,600 |
| 50 lb | 0.375 | 72 | 3,600 |
| 60 lb | 0.45 | 60 | 3,600 |
| 80 lb | 0.60 | 45 | 3,600 |
Bag counts are always rounded up to whole bags, never down, so the result errs on the side of having enough. Yields vary slightly by brand and mix type, so check the label on the bags you buy; if it lists a lower yield, use the higher bag count. There is no building code that specifies bag counts. Thickness and reinforcement come from your project plans and local rules, for example IRC R506 (concrete floors on ground), which sets a 3.5 in minimum for slabs, but local codes vary. This tool is a material estimator only. It is not engineering, permit or inspection approval.
Worked Example
You are pouring a 12 ft × 10 ft patio, 4 inches thick, using 50 lb bags with a 10% waste allowance.
- Volume: 12 × 10 × (4 ÷ 12) = 40 cubic feet.
- Cubic yards: 40 ÷ 27 = 1.48 yd³.
- Bags with no waste: 40 ÷ 0.375 = 106.67, so 107 bags.
- With 10% extra: 44 ÷ 0.375 = 117.33, rounded up to 118 bags.
- Weight: 118 × 50 lb = 5,900 lb, or 2.95 tons of dry mix.
- Cost at $6.25 per bag: 118 × $6.25 = $737.50.
Switching to 80 lb bags gives 44 ÷ 0.60 = 73.33, rounded up to 74 bags, with fewer trips to the wheelbarrow but heavier lifting.
Tips & Common Mistakes
- Don't skip the waste factor. Use 10% for a flat, well-prepared base and 15–20% for uneven subgrade, deep footings, or forms you cannot fully measure.
- Measure the real thickness. A slab nominally 4 inches thick is often 5 inches in spots on soft ground. Every extra inch on a 12 × 10 ft slab adds about 10 cubic feet, or roughly 27 more 50 lb bags.
- Don't mix up "per yard" and "per slab." Bags per cubic yard (45 to 90) is a constant for a bag size. Bags needed depends on your project.
- Buy the same brand and lot. Mixing bag types can change strength and color, and yields differ by product.
- Plan for the weight. A full cubic yard of 80 lb bags is 45 bags and 3,600 lb. Check your vehicle's payload before loading.
- Keep bags dry. Bags that got damp and partly hardened should be discarded, not used.
Frequently Asked Questions
How many bags of concrete are in a yard?
It depends on the bag size. A cubic yard needs about 90 bags of 40 lb, 72 bags of 50 lb, 60 bags of 60 lb, or 45 bags of 80 lb mix. Add about 10% extra for waste and uneven ground.
How many 80 lb bags of concrete make a yard?
Exactly 45 bags at a 0.60 cubic foot yield, since 27 ÷ 0.60 = 45. With a 10% waste allowance you should buy 50 bags.
How many 60 lb bags of concrete make a yard?
A cubic yard takes 60 bags of 60 lb concrete, based on a 0.45 cubic foot yield per bag. Round up to about 66 bags if you want a 10% safety margin.
How much does a cubic yard of concrete weigh?
Fresh, wet concrete weighs about 4,000 lb per cubic yard (roughly 150 lb per cubic foot), or about 2 tons. The dry bagged mix is lighter, about 3,600 lb per yard, because the water you add makes up the difference.
Is it cheaper to use bagged concrete or ready-mix?
For small jobs under about one cubic yard, bags are usually cheaper because ready-mix trucks charge minimum-load and delivery fees. Past one to two yards, ready-mix typically wins on both cost and labor, but local prices vary, so compare quotes.
How much extra concrete should I order?
Ten percent is the usual allowance for a flat, level slab. Go to 15–20% for irregular excavations, footings dug in loose soil, or if a shortfall would be hard to fix mid-pour.