Volume / cubic yards / bags
Concrete Calculator
A 10 x 10 ft slab 4 in thick holds 33.33 cu ft of concrete, which is 1.23 cu yd: 56 bags of 80 lb mix, 75 of 60 lb, 89 of 50 lb or 112 of 40 lb.
Sources checked
Your estimate
1.23 cu yd
33.33 cu ft of concrete, about 4,667 lb once mixed.
- 80 lb bags33.33 / 0.6 cu ft = 55.5656 bags
- 60 lb bags33.33 / 0.45 cu ft = 74.0775 bags
- 50 lb bags33.33 / 0.375 cu ft = 88.8989 bags
- 40 lb bags33.33 / 0.3 cu ft = 111.11112 bags
With 10% extra: 62 bags of 80 lb instead of 56.
How to calculate cubic yards of concrete
- The formula for concrete yardage is length times width times thickness, the thickness turned into feet: 10 x 10 x 4 / 12 = 33.33 cu ft.
- Divide by 27 cubic feet to the yard: 33.33 / 27 = 1.23 cu yd.
- Divide by what one bag yields and round up to whole bags: 33.33 / 0.6 = 55.56, so 56 bags of 80 lb. For other brands and weights see how many bags of concrete do I need; for the yield of each bag see how many bags of concrete in a yard.
- A round footing is pi x radius squared x depth; 4 footings 12 in across and 3 ft deep come to 9.42 cu ft. A form tube is the same cylinder, counted in bags by the Sonotube concrete calculator and, with the post taken out of the hole, by the fence post concrete calculator.
- Steps poured on the ground are blocks stacked from the bottom: width x rise x run x n(n + 1) / 2, which gives 12.83 cu ft for 3 steps 4 ft wide.
QUIKRETE's own calculator, run on the same 100 sq ft at 4 in, printed 112, 89, 75 and 56 bags of 40, 50, 60 and 80 lb; ours gives 112, 89, 75 and 56. Sakrete's slab calculator put the same pour at 51 of its 90 lb bags. A whole patio, with its gravel base, forms and joints, is planned by the concrete slab calculator.
Numbers we use
- One 40 lb bag yields
- 0.3 cu ftQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
- One 50 lb bag yields
- 0.375 cu ftQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
- One 60 lb bag yields
- 0.45 cu ftQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
- One 80 lb bag yields
- 0.6 cu ftQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
- Concrete weighs
- 140 lb per cu ftQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
- Extra over the volume
- 10%, shown beside the bare countSakrete concrete calculators page
- Thinnest pour for the mix
- 2 inQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
Concrete yardage for common slab sizes
| Slab | 4 in thick | 80 lb bags | 6 in thick | 80 lb bags |
|---|---|---|---|---|
| 4 x 4 ft | 0.2 cu yd | 9 | 0.3 cu yd | 14 |
| 10 x 10 ft | 1.23 cu yd | 56 | 1.85 cu yd | 84 |
| 12 x 12 ft | 1.78 cu yd | 80 | 2.67 cu yd | 120 |
| 10 x 20 ft | 2.47 cu yd | 112 | 3.7 cu yd | 167 |
| 20 x 20 ft | 4.94 cu yd | 223 | 7.41 cu yd | 334 |
| 24 x 24 ft | 7.11 cu yd | 320 | 10.67 cu yd | 480 |
What a cubic yard of concrete covers
| Thickness | 1 cu yd covers |
|---|---|
| 3 in | 108 sq ft |
| 4 in | 81 sq ft |
| 5 in | 64.8 sq ft |
| 6 in | 54 sq ft |
| 8 in | 40.5 sq ft |
Where sources disagree
How much to buy over the 33.33 cu ft of a 10 x 10 ft slab 4 in thick
- 10% more: 62 bags of 80 lbSakrete concrete calculators page
- Nothing more: 56 bags of 80 lbQUIKRETE Concrete Calculator (run 13 Oct 2026)
The calculator above prints the bare count and the count with 10% more, so you pick the margin yourself.
The thinnest slab a bag of concrete mix is for
- 2 in and thickerQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
- 4 in at least, over gravelSakrete High-Strength Concrete Mix data sheet (2023)
Below 4 in the two makers part ways, so a thinner pour is worth checking against the bag you buy.
Concrete calculator questions
How many cubic yards is a 10 x 10 slab?
At 4 in thick it is 1.23 cu yd (33.33 cu ft). At 6 in it grows to 1.85 cu yd, which is 84 bags of 80 lb mix.
How many square feet does a yard of concrete cover?
81 sq ft at 4 in thick, or 54 sq ft at 6 in. To go from square feet to cubic yards, multiply the area by the thickness in feet and divide by 27: 100 sq ft at 4 in is 1.23 cu yd.
How much ready-mix concrete should I order?
Order the cubic yards above plus a margin: 1.23 cu yd for the 10 x 10 slab, 1.36 with Sakrete's 10%. A small load can carry a short-load fee, which the concrete slab calculator shows for its own example.
How do I figure concrete for a triangle?
Half of the rectangle around it. A triangle with a 10 ft base and 10 ft height at 4 in thick holds 16.67 cu ft, 0.62 cu yd: enter the base and height as length and width, then halve the answer.
How much concrete do 3 steps take?
3 steps 4 ft wide with a 7 in rise and an 11 in run hold 12.83 cu ft, or 0.48 cu yd. That is 22 bags of 80 lb if the steps sit on the ground with no hollow under them.
How much does the concrete in a 10 x 10 slab weigh?
About 4,667 lb at 4 in thick: QUIKRETE's 1101 sheet gives 140 lb per cubic foot of concrete, and the slab holds 33.33 cu ft.
Should I buy extra concrete for a slab?
Sakrete's calculators add 10%, which turns 56 bags of 80 lb into 62 for a 10 x 10 ft slab at 4 in. QUIKRETE's calculator adds nothing and says so on the page.
How thin can a concrete slab be?
QUIKRETE sells its Concrete Mix for pours 2 in thick and up. Sakrete's flatwork instructions want 4 in of concrete at least when it goes over a gravel base.
A planning aid, not an engineering calculation: your local code and building inspector have the final word. Terms