How Many Bags of Concrete Do I Need?

Find your bag size in the yield table below to see how much volume each bag mixes to, or find your slab size and thickness in the second table for a ready bag count. These figures use the manufacturer's published yield per bag with no waste buffer added. For an exact count from your own dimensions — including a post hole, a footing, or a slab thickness not listed here — the concrete calculator computes cubic yards and bag count directly from length, width, and thickness. This page is a scannable reference for common sizes plus the yield math behind the numbers.

Bag yield by size

Every bag of pre-mix concrete lists its mixed yield in cubic feet on the bag — the figures below come from Quikrete's published Concrete Mix (No. 1101) yield chart, and Sakrete publishes comparable yields for its equivalent general-purpose mixes. Divide your project's volume (in cubic feet) by a bag's yield to get the raw bag count, then round up, since bags are sold whole.

Bag yield figures (40 lb ≈ 0.30 cu ft, 60 lb ≈ 0.45 cu ft, 80 lb ≈ 0.60 cu ft): Quikrete Concrete Mix technical data / yield chart, corroborated by NRMCA consumer guidance on approximate bags per cubic yard. A 40 lb bag is the easiest single bag for one person to lift and mix by hand but needs the most bags for a given volume; an 80 lb bag cuts the bag count roughly in half compared to 40 lb, at exactly double the per-bag weight.

Bags needed by slab size and thickness

The table below applies the 60 lb and 80 lb yields above to a few common slab footprints at two typical thicknesses — 4" for a patio, walkway, or shed pad, and 6" for a driveway or anything that will see vehicle weight. Each figure is volume (area × thickness) divided by bag yield, rounded up, with no waste buffer added — add a bag or two for spillage and an uneven sub-base on any real pour.

Bagged concrete is a practical choice up through roughly a cubic yard of material — beyond that, both the bag count and the mixing labor climb fast, and ready-mix delivery usually becomes more practical. Run your own footprint through the concrete calculator to see the crossover point for your project.

Total weight, not just bag count

A bag count alone can understate the job, since the weight adds up fast. A 10x10 ft patio at 4" thick, from the table above, is 75 bags of 60 lb — that's 4,500 lb of bagged material to move from the pallet to the mixing area, before any water is added. The same slab in 80 lb bags is 56 bags, or 4,480 lb. Bag size changes how many individual bags you handle, not the total weight, since the underlying volume is identical either way (the small gap between the two totals is only each column's round-up to a whole bag). Splitting a large pour into more, smaller batches (mixing and placing one wheelbarrow load at a time rather than staging every bag beside the form first) is standard practice for exactly this reason: it turns one two-ton moving job into a series of 60 or 80 lb lifts spread across the pour, rather than one large stack to relocate up front.

Bags per post hole by diameter and depth

A fence post or deck footing hole is round, so the table below uses the exact cylinder volume (π × radius² × depth) for a few common auger and hand-dug sizes. Entering the diameter as both length and width in the concrete calculatoroverstates a round hole by about 27% (4/π ≈ 1.27) — that page's FAQ covers the correction and how to enter several identical holes at once.

A deeper frost-line footing in a cold-winter region often means a narrower, taller hole rather than a wider one — an 8" or 10" diameter auger is standard rental equipment, so depth is usually the variable that changes by region and post load, not diameter. That is why the table steps through depth as well as width: going from 3 ft to 4 ft on a 12" hole adds a third more concrete, and at least one more bag per hole in either bag size.

Worked example: a 12" deck pier poured 42" deep

A depth that isn't in the table works the same way: convert the hole to cubic feet first, then divide by bag yield. Take a single 12" diameter deck pier (a common cardboard form-tube size) set 42" deep to reach a cold-region frost line. The radius is 6", or 0.5 ft, and the depth is 3.5 ft, so the volume is π × 0.5² × 3.5 = 3.14159 × 0.25 × 3.5 ≈ 2.75 cubic feet. At 0.45 cu ft per 60 lb bag, that's 2.75 / 0.45 = 6.11 bags, rounded up to 7. At 0.6 cu ft per 80 lb bag: 2.75 / 0.6 = 4.58 bags, rounded up to 5. The 60 lb figure sits just past a whole bag, so rounding up leaves most of a bag spare — a reasonable margin for a hole that's rarely dug to a perfectly clean cylinder. If the form tube stands above grade, add that extra height to the depth before calculating.

Hand mixing versus a rented mixer

The bag counts above translate directly into mixing labor, since each bag is generally mixed on its own (in a wheelbarrow or mixing tub) before being placed. A handful of bags — the 4x4 ft pad or a single post hole in the tables above — is a reasonable afternoon of hand mixing with a hoe or mixing paddle, one batch at a time. As the bag count climbs into the larger patio and driveway-apron rows, hand mixing each batch individually becomes the slow part of the job well before the material itself is the limiting factor, since every batch has to be placed before the previous one starts to stiffen. A rented drum or paddle mixer turns each batch faster than hand mixing can, which keeps a larger pour moving as one continuous placement instead of a series of increasingly rushed batches — worth weighing against the rental cost and setup time once a job's bag count moves well past what a single person can comfortably hand-mix and place in one session.

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