Concrete Mix Chart: Bags Per Cubic Yard by Strength

A cubic yard is 27 cubic feet

Concrete is sold by the cubic yard, but slabs are measured in feet and inches — so the first step is always the conversion. The volume is length × width × depth / 12: on the defaults — length 10.00 ft, width 10.00 ft, depth 4.00 in, strength 4,000 psi, bag size 60-lb — the volume is 33.33 cu ft (1.23 cu yd), the premixed bags are 75 and the cement sacks are 9 (unrounded 8.0247). Also shown: 56 x 80-lb bags and 112 x 40-lb bags.

Concrete mix chart — nominal mixes by strength

At the defaults — length 10.00 ft, width 10.00 ft, depth 4.00 in, strength 4,000 psi, bag size 60-lb — the volume is 33.33 cu ft (1.23 cu yd), the premixed bags are 75 and the cement sacks are 9 (unrounded 8.0247). Check the identities: volume (cu ft) = length × width × depth / 12; volume (cu yd) = cu ft ÷ 27; premixed bags = ceil(volume ÷ bag yield); cement sacks = ceil(cu yd × sacks per cu yd). Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum.

The worked example, line by line

Setup: length 10.00 ft, width 10.00 ft, depth 4.00 in, strength 4,000 psi, bag size 60-lb.

Line 1 — the volume. 10 × 10 × 4 / 12 = 33.33 cu ft (exact 33.3333). Divide by 27 for cubic yards: 33.3333 / 27 = 1.23 cu yd (exact 1.2346).

Line 2 — the premixed bags. A 60-lb bag yields 0.45 cu ft, so 33.3333 / 0.45 = 74.07 — and bags round up, so 75 bags. An 80-lb bag yields 0.60 cu ft, so 33.3333 / 0.60 = 55.56, rounded up to 56 bags; a 40-lb bag yields 0.30 cu ft, so 33.3333 / 0.30 = 111.11, rounded up to 112 bags.

Line 3 — the cement sacks. At 4,000 psi the mix takes 6.5 sacks per cubic yard: 1.2346 × 6.5 = 8.0247 — and sacks round up, so 9 sacks of 94-lb cement.

Reverse: the length for exactly 75 bags at 60-lb is 10.125 ft — the star is a length (exact boundary volume 33.75 cu ft); at L 10.12 ft the volume is 33.73 cu ft (75 bags), at L 10.13 ft it is 33.77 cu ft (76 bags). The depth for a volume of exactly 50.00 cu ft is 6.00 in; at 6.00 in the volume is 50.00 cu ft, at 5.99 in it is 49.92 cu ft, at 6.01 in it is 50.08 cu ft. The length for exactly 100 bags at 60-lb is 13.50 ft — the top of the 100-bag band; at L 13.50 ft the volume is 45.00 cu ft (100 bags), at L 13.51 ft it is 45.03 cu ft (101 bags), at L 13.49 ft it is 44.97 cu ft (100 bags). The depth for 56 bags at 80-lb is 4.032 in (exact 4.0320); at D 4.03 in the volume is 33.58 cu ft (56 bags), at D 4.04 in it is 33.67 cu ft (57 bags). The length for 9 cement sacks at 4,000 psi is 9.9692 ft — the star is a length; at L 9.97 ft the cubic yards are 1.2309, unrounded sacks 8.0006 (9 sacks), at L 9.96 ft the cubic yards are 1.2296, unrounded sacks 7.9926 (8 sacks). The width for a volume of exactly 40.00 cu ft is 12.00 ft — the star is a width; at 12.00 ft the volume is 40.00 cu ft, at 11.99 ft it is 39.97 cu ft, at 12.01 ft it is 40.03 cu ft.

Every branch, checked

Length 20 ft: Volume 66.67 cu ft (2.47 cu yd), 149 bags, 17 sacks. Doubling the length doubles the volume — the bags go from 75 to 149 and the sacks from 9 to 17.

Depth 6 in: Volume 50.00 cu ft (1.85 cu yd), 112 bags, 13 sacks. Six inches instead of four is half as much again: the volume is 50.00 cu ft, the bags are 112 and the sacks are 13.

Strength 3,000 psi: Volume 33.33 cu ft (1.23 cu yd), 75 bags, 7 sacks. The volume and bags are unchanged — strength only changes the cement share — so the sacks fall to 7 (unrounded 6.7901).

Bag 80-lb: Volume 33.33 cu ft (1.23 cu yd), 56 bags, 9 sacks. Bigger bags mean fewer of them: 56 instead of 75 — the sacks stay at 9, because the cement does not care how the premix is bagged.

Length 12 ft, width 8 ft: Volume 32.00 cu ft (1.19 cu yd), 72 bags, 8 sacks. A 12-by-8 slab is 96 square feet against 100, so the volume is 32.00 cu ft, the bags are 72 and the sacks are 8.

Depth 8 in: Volume 66.67 cu ft (2.47 cu yd), 149 bags, 17 sacks. Eight inches is twice four, so the volume doubles to 66.67 cu ft, the bags to 149 and the sacks to 17.

Strength 2,000 psi: Volume 33.33 cu ft (1.23 cu yd), 75 bags, 6 sacks. The weakest mix takes the least cement — 6 sacks (unrounded 5.5556).

Bag 40-lb: Volume 33.33 cu ft (1.23 cu yd), 112 bags, 9 sacks. The smallest bags mean the most of them: 112 instead of 75 — the sacks stay at 9.

What the defaults assume

The model assumes a rectangular slab with a constant depth, the manufacturer-standard bag yields (40-lb 0.30 cu ft, 60-lb 0.45 cu ft, 80-lb 0.60 cu ft) and the standard nominal mixes — the ratios are by volume, and suppliers vary. It assumes no waste, no spillage and no uneven subgrade — the bags already round up to whole bags, which covers a little of it. It does not model reinforcement, control joints, curing, or the water you add — the sacks are cement only, and a cubic yard of mixed concrete needs sand and gravel on top of them. With a 0 ft length the volume is 0.00 cu ft, the bags are 0 and the sacks are 0 — a calc-valid input that renders 0. At the maximum inputs — 100 ft by 100 ft, 12 in deep — the volume is 10,000.00 cu ft (370.37 cu yd), the bags are 22,223 and the sacks are 2,408 (unrounded 2,407.4074). A depth of 0 in is a validation error at the calc level — depth must be over 0 — so no live calc result is claimed for it. Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum; the reverses are nearest-value solutions, and the exact unrounded figures (10.125, 6.00, 13.50, 4.0320, 9.9692, 12.00) are stated wherever the rounded figures appear.

Output · formula · meaning

Who uses this

• The homeowner pouring a 10-by-10 patio: they learn it takes 75 sixty-pound bags — or 9 sacks of cement if they mix it themselves — and they check the 6-inch branch (112 bags) before they dig deeper.
• The DIYer mixing their own concrete: they learn 4,000 psi takes 6.5 sacks per cubic yard — and they check the 3,000 psi branch (7 sacks) to see what a weaker mix saves.
• The contractor pricing a long slab: they learn a 20-foot slab takes 149 bags and 17 sacks — and they check the 12-by-8 branch (72 bags) for the odd-sized pour.
• The shopper choosing a bag size: they learn 80-lb bags mean 56 bags instead of 75 — and they check the 40-lb branch (112 bags) to see the other end of the range.

Accuracy & limitations

The math is first-principles volume: volume (cu ft) = length × width × depth / 12; volume (cu yd) = cu ft ÷ 27; premixed bags = ceil(volume ÷ bag yield); cement sacks = ceil(cu yd × sacks per cu yd). The 4-decimal exact is shown where the rounding matters: the length for 9 cement sacks at 4,000 psi is 9.9692 (shown as 9.97 ft); at L 9.97 ft the unrounded sacks are 8.0006 (9 sacks), at L 9.96 ft they are 7.9926 (8 sacks). The depth for 56 bags at 80-lb is 4.0320 in (shown as 4.03 in); at D 4.03 in the volume is 33.58 cu ft (56 bags), at D 4.04 in it is 33.67 cu ft (57 bags). What the model cannot do is measure your site: the mixes are nominal and suppliers vary, the bag yields are manufacturer standards, and structural work — footings, foundations, load-bearing slabs — needs an engineered mix, not a nominal one. For the driveway the slab sits in, see the concrete vs asphalt driveway comparison; for the caulk that seals it, see the caulk coverage chart. This is a calculator, not a structural opinion.