Bags of concrete calculator: how many 80, 60, 50 or 40 lb bags do I need?

Forty-five. A cubic yard is 27 cubic feet and an 80 lb bag of standard mix yields 0.60 cubic feet, so 27 ÷ 0.60 = 45 exactly. The same yard is 60 bags of 60 lb, 72 of 50 lb or 90 of 40 lb, because every size is 133 lb of dry mix per cubic foot and 3,600 lb per yard. Those are bags of concrete in the ground; with the calculator's 10 percent waste a yard of purchase is 50, 66, 80 or 99 bags. A pallet of 42 does not reach a yard.

Cubic feet of the pour, plus waste, divided by the yield on the bag and rounded up; the calculator above does it for a slab, a round pier or a typed volume in all four bag sizes. The job-by-job answers, fence posts, steps, mailbox, mower pad, are in how many bags of concrete do I need.

About 0.60 cubic feet, which is 0.022 cubic yards, or a patch 1.8 sq ft at 4 in thick, 3.6 sq ft at 2 in, 1.2 sq ft at 6 in. The figure is the yield printed on a standard concrete mix bag and it is what this calculator divides by; a 60 lb bag makes 0.45, a 50 lb 0.375, a 40 lb 0.30. Fast-setting and high-strength blends list their own, usually close but not identical, so read the bag when the count is tight. The 80 lb bag wants roughly 3 quarts of water to start.

62 bags of 80 lb at 4 in with 10 percent waste, or 56 without, and 82, 98 or 123 at 60, 50 and 40 lb; the full answer by thickness is on the concrete calculator.

Forty-two bags of 80 lb or 56 bags of 60 lb for standard concrete mix, the counts retailer and supplier listings agree on; each pallet is 3,360 lb of dry mix and makes 25.2 cubic feet of concrete. Forty-pound bags are usually listed at 80 to a pallet and 50 lb bags anywhere from 42 to 64, depending on the product, so those two are worth confirming on the quotation. Pallet counts are packaging, not a standard: a crack-resistant or high-strength product in the same bag weight can ship a different count.

No. Forty-two bags of 80 lb make 42 × 0.60 = 25.2 cubic feet, which is 0.93 of a cubic yard; a yard needs 45 bags, three more. The pallet-equals-a-yard rule of thumb comes from a manufacturer's estimating post and is fine for a first guess, but on a pour sized at exactly a yard it leaves you three bags short, and with the 10 percent waste the tool applies, eight short. The default 10 × 10 slab here needs 62 bags: one pallet plus 20 loose.

Usually one to four bags of 80 lb for a 4×4 in an 8 to 12 in hole 2 to 3 ft deep, but the honest count subtracts the post from the hole and depends on the frost depth; the post hole concrete calculator does both.

Before, and once. Add the waste to the volume in cubic feet, then divide by the yield and round up. Adding it after gives the same bag count a second margin, so 62 becomes 69 on a 10 × 10 slab, and rounding twice can add one more. The calculator applies the percentage to the volume in every mode, including when you type a volume in, so if that volume already includes a margin from another tool, set the waste here to 0. The 10 percent covers spillage, a slightly low subgrade and the concrete left in the mixer, not compaction; concrete does not compact like gravel.

Because a part of a bag has to be bought as a bag. The default slab is 36.67 cubic feet with waste, and 36.67 ÷ 0.60 = 61.1 bags; the 0.1 is 0.06 cubic feet, a corner of the form that would otherwise be short. The tool rounds up at the very end, on the total, never per row, and when you set a quantity above one it rounds the total once and the per-shape figure separately, so the two can disagree by a bag or two. Any calculator that prints a decimal bag count, or rounds to the nearest, is leaving that corner to you.

Yes, by the same ratio as the weight: 0.375 cubic feet against 0.45, so a yard is 72 bags of 50 lb against 60 bags of 60 lb. People mix the two up because fast-setting mix is commonly sold in 50 lb bags and standard mix in 60, and the two products are used for different jobs; a fast-setting bag lists its own yield, so the bag is the reference. On a pier that needs 5 bags of 80 lb, the 50 lb count is 7 and the 60 lb count is 6, from the table under the result.

Five bags of 80 lb with 10 percent waste, or 6 of 60 lb, 7 of 50 lb, 9 of 40 lb. The tube is 12 in across, so the radius is 6 in and the volume is π × 0.5² × 3 = 2.36 cubic feet, 2.59 with waste, 4.3 bags rounded up to 5. That is a solid tube with nothing in it; if a post or a saddle sits in the wet concrete the count barely moves, but a post that runs the full depth changes it, and the post hole calculator subtracts it. A 4 ft tube of the same size is 6 bags.

Fourteen bags of 80 lb, 15 with 10 percent waste. Twenty-four inches is 2 ft, so the pier is 2 × 2 × 2 = 8 cubic feet, and 8 ÷ 0.60 = 13.3, rounded up to 14; with waste, 8.8 ÷ 0.60 = 14.7, so 15. The same numbers typed as feet give 13,824 cubic feet and 23,040 bags, which is what one published reply to this exact question said. Any pier count in the thousands is a unit error. Enter the pier in the calculator as a rectangle, 2 ft by 2 ft by 24 in, and it prints 15.

About 3 quarts to start for standard mix, then more as needed up to roughly 4½, until the mix is stiff and workable with no dry pockets; a 60 lb bag starts near 2 quarts and a 40 lb near 1½. Those are label figures and the bag is the reference. Multiplied out, a yard of 80 lb bags is about 34 gallons carried to the mixer, which is part of the case for a truck past one yard. Too much water is the common mistake and it lowers strength; the ratio and what it does are in concrete mix ratios, water and PSI.

A shortcut for a 4 in slab: square feet times 0.6 gives the 80 lb bags, waste included; times 0.8 for 60 lb; times 1 for 50 lb. A square foot at 4 in is a third of a cubic foot, and a third divided by 0.60 is 0.556 bags, so the 0.6 carries an 8 percent margin; the 60 lb factor is really 0.741 with 8 percent, and the 50 lb factor 0.889 with 12 percent. It is a fair check on a delivery, but it only holds at 4 in and the margin changes by bag size; at 6 in the factors are 0.9, 1.2 and 1.5.

Around one cubic yard, which is where the calculator adds its note: a yard is 45 bags of 80 lb, 3,600 lb lifted four times and 45 bags through the mixer, and past that most people order a truck. Under half a yard, an equipment pad or a run of post holes, bags win because a plant will not send a truck for it or will charge a short-load fee. Between the two it depends on your mixer, your help and the delivery window; the break-even by volume and labour is in bagged concrete vs ready-mix.

Two bags of 80 lb, because one makes 0.60 cubic feet and 1 ÷ 0.60 = 1.67, rounded up. Three bags of 60 lb (1 ÷ 0.45 = 2.2), three of 50 lb (2.7) or four of 40 lb (3.3). The rounding is unkind at this scale, which is why small jobs are better counted from the exact volume: a 12 in tube 3 ft deep is 2.36 cubic feet and needs 5 bags of 80 lb with waste, not the 6 you would get by rounding each cubic foot up on its own. Type the shape into the calculator and it rounds once.