How Many Bags of Concrete Do I Need? Yields, Slab Math and When to Order a Truck

To work out how many bags of concrete you need, figure the volume in cubic feet and divide by the bag’s yield: an 80 lb bag makes about 0.6 cubic feet and a 60 lb bag about 0.45. That puts one cubic yard at 45 bags of 80s or 60 bags of 60s, before you add anything for waste.

How many bags of concrete do I need?

Divide the volume in cubic feet by the bag’s yield. An 80 lb bag makes about 0.6 cubic feet and a 60 lb bag about 0.45, so a cubic yard takes 45 bags of 80s or 60 bags of 60s. A 10 by 10 slab at 4 inches needs 56 bags of 80s, plus about 10 percent for waste.

How much concrete one bag makes

Yield is listed in the maker’s product data. Sakrete lists 0.6 cubic feet for its 80 lb High-Strength Concrete Mix and 0.45 cubic feet for the 60 lb bag, both 4,000 psi mixes. Quikrete sells its standard Concrete Mix in 40, 50, 60 and 80 lb bags, also at 4,000 psi.

Both published yields work out to 0.0075 cubic feet per pound of dry mix. For a 40 or 50 lb bag, use the yield the maker lists for that product rather than scaling from these.

Bag size	Yield per bag	Bags per cubic yard	Dry mix per cubic yard	Bags for 100 sq ft at 4 in.
80 lb	0.60 cu ft	45	3,600 lb	56
60 lb	0.45 cu ft	60	3,600 lb	75

60 vs 80 lb bags

The concrete is the same. A cubic yard takes 3,600 pounds of dry mix either way (45 × 80 or 60 × 60), so the choice is about handling. Sixties are easier to carry and dump into a mixer. Eighties mean fewer bags to cut open and fewer trips to the truck.

The yardage formula, from slab size to bags

Work in feet and round up at the end:

1. Length × width = square feet.
2. Square feet × thickness in feet = cubic feet. Divide inches by 12: 4 in. is 0.333 ft, 5 in. is 0.417 ft, 6 in. is 0.5 ft.
3. Cubic feet ÷ 27 = cubic yards. That’s how ready-mix is ordered.
4. Cubic feet ÷ bag yield = bags.

Thickness drives the whole number. Going from 4 to 6 inches adds half again as much concrete. Our guide to how thick a concrete patio should be covers which thickness fits which use, and the article on concrete driveway thickness covers slabs that carry vehicles.

Skip the hand math: our free concrete calculator works out cubic yards and 40, 60 or 80 lb bags for slabs, footings, piers and steps.

Concrete for a 10×10 slab, worked out

A 10 by 10 foot slab, 4 inches thick:

• 10 × 10 = 100 square feet
• 100 × 0.333 = 33.3 cubic feet
• 33.3 ÷ 27 = 1.23 cubic yards
• 33.3 ÷ 0.6 = 55.6, so 56 bags of 80 lb mix (or 33.3 ÷ 0.45 = 74.1, so 75 bags of 60s)
• With 10 percent extra: 62 bags of 80s or 82 bags of 60s

At 6 inches, the same slab is 50 cubic feet, 1.85 cubic yards and 84 bags of 80s before waste.

Slab, 4 in. thick	Cubic feet	Cubic yards	80 lb bags	With 10% extra
8 × 8 ft	21.3	0.79	36	40
10 × 10 ft	33.3	1.23	56	62
10 × 12 ft	40.0	1.48	67	74
12 × 12 ft	48.0	1.78	80	88
12 × 16 ft	64.0	2.37	107	118

How many bags for a post hole

A post hole is a cylinder, and the post fills part of it. Quikrete’s concrete calculator pairs a 4 inch post with a 12 inch hole and suggests a hole half as deep as the post stands above ground: 3 feet in the ground for a 6 foot fence.

For a 4×4 (3.5 inches square) in a 12 inch hole, 3 feet deep:

• Hole: 3.14 × 0.5 × 0.5 × 3 = 2.36 cubic feet
• Post: 0.292 × 0.292 × 3 = 0.26 cubic feet
• Concrete: about 2.1 cubic feet, which is 3.5 bags of 80s (buy 4) or 4.7 bags of 60s (buy 5)

Ten fence posts at that size take about 35 bags of 80s, close to 0.8 cubic yards. Deck and pergola posts are different: their footing depth comes from the building code and your local frost line, not a fence rule of thumb. Our guide to anchoring a pergola to pavers covers footings for posts that carry a structure.

Add for waste and an uneven base

Published yields assume a perfectly flat, full pour. Quikrete notes that its calculator yields don’t allow for an uneven base or waste, and that’s where bag counts come up short.

A base that runs half an inch low across a 10 by 10 slab swallows another 4.2 cubic feet, about 7 more bags of 80s. Add spillage, a bag that gets wet and the concrete left in the mixer, and 10 percent extra on a slab is a sensible plan. Post holes dug by hand tend to come out wider than planned, so buy an extra bag or two there as well.

Related: how long to wait before driving or parking on new concrete

Bagged concrete vs ready-mix: finding the break-even

Price is only half of it. Every cubic yard of bagged concrete is 45 bags of 80s, or 3,600 pounds you lift from the store shelf, into the truck, off the truck and into the mixer. The 10 by 10 slab above is 56 bags, almost 4,500 pounds.

A slab also has to be placed and finished in one go. With one small mixer, the first batch can be stiffening at the far end while you’re still mixing the last. On bigger pours, keeping up is a bigger problem than the cost.

To compare the money without guessing, get three numbers: the price of one bag, the plant’s price per cubic yard, and its fixed charges for your order (delivery, plus any short-load fee for a small order). Then:

• Bag cost per yard = 45 × the price of an 80 lb bag
• Break-even yards = fixed truck charges ÷ (bag cost per yard − ready-mix price per yard)

Below the break-even, bags cost less. Above it, the truck does. Ask the plant for its minimum load and whether the truck can reach your forms, because a chute that can’t reach means wheelbarrows anyway.

DIY or hire it out

Bags are the right call for post holes, small pads, steps and repairs under about a cubic yard. Hire a crew or order a truck when:

• The slab is over a cubic yard, or you can’t mix and place it in one continuous pour
• It needs a compacted base, forms on a slope, reinforcement or saw-cut joints
• It carries a vehicle, a hot tub or a structure

Pouring steps? Our free concrete steps calculator works out the risers, treads and run from your total rise, plus the concrete and 40, 60 or 80 lb bags to pour them.

If you’re still weighing concrete against pavers, our comparison of paver patios and concrete patios lays out the tradeoffs. And if you’d rather have the patio drawn to scale with its dimensions and materials before you buy a single bag, our online patio design plans start at $349; the Build-Ready plan ($1,795) adds construction details and a quantity takeoff.

Frequently Asked Questions

How many 80 lb bags of concrete are in a yard?

45 bags. A cubic yard is 27 cubic feet, and each 80 lb bag yields about 0.6 cubic feet, so 27 ÷ 0.6 = 45. That’s 3,600 pounds of dry mix, the same as 60 bags of 60s.

How many 60 lb bags of concrete make a yard?

60 bags, at about 0.45 cubic feet each. That’s the same 3,600 pounds of dry mix as 45 bags of 80s.

How many bags of concrete for a 10×10 slab?

At 4 inches thick, 56 bags of 80 lb mix or 75 bags of 60 lb mix, before waste. Buy about 10 percent more: 62 bags of 80s or 82 of 60s.

How many bags of concrete per fence post?

For a 4×4 set 3 feet deep in a 12 inch hole, about 2.1 cubic feet: four 80 lb bags or five 60s.

Is it cheaper to use bags or ready-mix concrete?

It depends on your bag price, the plant’s price per yard and its delivery and short-load charges. Run the break-even formula above for your exact yardage, and remember that past about a yard, mixing and placing time matters as much as cost.

How many 50 lb bags of concrete make a yard?

72 bags. Quikrete lists a 50 lb bag of its Concrete Mix at about 0.375 cubic feet, and 27 ÷ 0.375 = 72. That’s the same 3,600 pounds of dry mix as 45 bags of 80s. A 40 lb bag yields about 0.30 cubic feet, so a yard takes 90 of those.

How many square feet does an 80 lb bag of concrete cover?

About 1.8 square feet at 4 inches thick, since the bag yields about 0.6 cubic feet. At 6 inches it covers 1.2 square feet. At 2 inches, the thinnest pour Quikrete designs its Concrete Mix for, it covers about 3.6 square feet.

How much water goes in an 80 lb bag of concrete?

Quikrete calls for a final water content of about 6 to 9 pints per 80 lb bag of its Concrete Mix. Start at the low end, add water a little at a time until the mix is workable, and stay inside the range the maker lists for your product.

How long does bagged concrete need to cure?

Quikrete says to keep curing its Concrete Mix for 5 days in weather at 70 degrees F or warmer and 7 days at 50 to 70 degrees F, and to protect it from freezing for the first 48 hours. For a fence post, wait 24 hours before putting any strain on it.

Sources: Sakrete High-Strength Concrete Mix 80 lb (yield 0.6 cu ft), Oldcastle APG; Sakrete High-Strength Concrete Mix 60 lb (yield 0.45 cu ft), Oldcastle APG; Quikrete Concrete Mix No. 1101 product page; Quikrete Concrete Calculator; Quikrete Concrete Mix No. 1101 data sheet (yields, water, curing)

Written and reviewed by Thayne Muthler, owner of Muthler Landscaping & Construction. How we check facts: editorial policy.