Concrete Bag Calculator

1. Choose an input mode: slab dimensions, or a known volume and unit.
2. Enter the dimensions (length and width in feet, thickness in inches) or the volume, with a waste allowance.
3. Optionally enter the price per bag for each size to compare the cost per cubic yard.
4. Read how many bags of each size you need, and which gives the best value.

Here is what each result means:

A concrete bag calculator tells you how many bags of pre-mixed concrete a project needs. Pre-mixed bags already contain cement, sand and gravel, so you just add water, which makes them ideal for small pours.

The number of bags depends on the bag size, because each size yields a set volume of concrete: an 80 pound bag makes about 0.60 cubic feet, a 60 pound bag 0.45, and so on. This tool works out the bags for every common size at once, so you can weigh fewer heavy bags against more light ones, and, with prices, see which costs least per cubic yard. For a large pour, ready-mix is usually cheaper, which the concrete cost calculator can confirm.

The volume is the slab or void size, plus a waste allowance. Dividing by the bag yield gives the number of bags, rounded up, because a part bag still has to be bought.

1. Find the volume in cubic feet from the dimensions or the entered volume, and add waste.
2. Divide by the bag yield for each size: 0.60, 0.45, 0.375 and 0.30 cubic feet.
3. Round each up to whole bags.
4. With bag prices, multiply bags by price and divide by the cubic yards for the cost per yard.

Suppose you are pouring a 10 by 10 foot slab, 4 inches thick, with a 10 percent waste allowance.

Calculation: volume = 10 x 10 x (4 / 12) = 33.33 cu ft, plus 10 percent is 36.67 cu ft (1.36 cu yd). Dividing by the yields gives 62 eighty-pound bags, 82 sixty-pound, or 123 forty-pound bags.

Sixty-plus bags is a lot of mixing, so at this size most people compare the bagged cost against a short-load ready-mix delivery before deciding.

Three things change the bag count: the bag size (its yield), the thickness or volume of the pour, and the waste allowance. Bag size is the biggest: each yields a set volume, as the table shows, with the bags per full cubic yard (27 cubic feet).

Yields are typical for pre-mixed concrete and vary a little by product, so check the figure printed on the bag.

Larger bags mean fewer bags and usually a lower cost per cubic yard, but each one is heavier to carry and mix. The best choice balances price against what you can handle.

Enter the price for each size and the calculator names the cheapest per cubic yard, which is not always the biggest bag once local prices are in.

Small Pours and Repairs

Footings, post bases, small slabs and patches, where a ready-mix truck is not worth the delivery and short-load fees.

Awkward Access

Where a truck or barrow cannot reach, bags can be carried in and mixed on the spot.

Deciding Bagged vs Ready-mix

Once a job needs dozens of bags, price the bagged total against a ready-mix delivery with the concrete cost calculator.

1. Using the Wrong Yield

Bag yields differ by product. Using 0.60 for a bag that yields less leaves you short. Check the printed yield.

2. Forgetting Waste

Spillage and an uneven base mean you use more than the exact volume. Add a 5 to 10 percent allowance.

3. Confusing Concrete with Cement Bags

A pre-mixed concrete bag has aggregate; a Portland cement bag is powder only. The cement calculator handles the latter.

4. Picking the Biggest Bag on Price Alone

A big bag can be cheaper each but not per yard. Compare cost per cubic yard, not per bag.

5. Bagging a Large Pour

Past a cubic yard or two, mixing dozens of bags is slow and often dearer than ready-mix. Compare before you commit.

The arithmetic is exact for the volume, yields and prices you enter; the bag count depends on the real yield of the product.

About 45. An 80 pound bag yields roughly 0.60 cubic feet, and a cubic yard is 27 cubic feet, so 27 divided by 0.60 is 45 bags. A 60 pound bag yields about 0.45 cubic feet, which is about 60 bags per yard.

For a 10 by 10 foot slab at 4 inches thick, about 62 eighty-pound bags with a 10 percent waste allowance, or 82 sixty-pound bags. That is a lot of mixing, so compare it against ready-mix at this size.

Find the volume in cubic feet, add a waste allowance, then divide by the bag yield and round up. For 36.67 cubic feet at 0.60 cubic feet per 80 pound bag, that is 62 bags.

An 80 pound bag yields about 0.60 cubic feet and a 60 pound bag about 0.45, so you need fewer 80 pound bags. The 80 pound bag is usually cheaper per cubic yard but heavier to lift.

Larger bags are usually cheaper per cubic yard, but it depends on local prices. Enter the price for each size and the calculator names the cheapest per cubic yard, which is not always the 80 pound bag.

By volume, an 80 pound bag covers about 0.60 cubic feet, which is roughly a 2 foot by 2 foot area at a bit under 2 inches thick. Coverage depends on the thickness you pour.

For small pours, yes, once you include ready-mix delivery and short-load fees. For larger pours, ready-mix is usually cheaper by the yard. Compare the totals with the concrete cost calculator.

Yes, 5 to 10 percent for spillage and an uneven base. Running short mid-pour means a trip back for more bags, so round up and keep a spare.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• QUIKRETE Concrete Mix product data (QUIKRETE; bag sizes and yields).
• QUIKRETE concrete and bag calculator (QUIKRETE; bag-count method).
• National Ready Mixed Concrete Association (NRMCA; bagged versus ready-mixed concrete).
• American Cement Association (Portland Cement Association) (American Cement Association; concrete basics).