Concrete Calculator
Find how much concrete you need in cubic yards and bags.
You need
1.23 cubic yards
- 80 lb bags
- 56 bags
- 60 lb bags
- 75 bags
- Cubic feet
- 33.3 ft³
You need about 1.23 cubic yards (33.3 ft³) of concrete. Mixing it yourself, that is 56 bags of 80 lb or 75 bags of 60 lb premix.
Calculation breakdown
| Step | Formula | Result |
|---|---|---|
| Area | 10 × 10 | 100.00 sq ft |
| Thickness in feet | 4 in ÷ 12 | 0.3333 ft |
| Volume of one | 100 × 0.3333 | 33.33 ft³ |
| Cubic yards | 33.33 ÷ 27 | 1.23 yd³ |
| 80 lb bags | 33.33 ft³ ÷ 0.6 ft³, rounded up | 56 bags |
How it works
The calculator finds the volume of concrete for one slab or hole, multiplies by how many you need, adds any extra you ask for, then converts the total to cubic yards and bags.
Worked example
A patio slab 10 ft long, 10 ft wide and 4 in thick:
- Thickness in feet: 4 ÷ 12 = 0.333 ft
- Volume: 10 × 10 × 0.333 = 33.33 ft³
- Cubic yards: 33.33 ÷ 27 = 1.23 yd³
- 80 lb bags: 33.33 ÷ 0.60 = 55.6, rounded up to 56 bags
- 60 lb bags: 33.33 ÷ 0.45 = 74.1, rounded up to 75 bags
At $150 per cubic yard for ready-mix, 1.23 yd³ costs about $185.19 before delivery charges.
Where the bag yields come from
Bag counts use the yields printed on the manufacturers’ data sheets: about 0.60 ft³ for an 80 lb bag and 0.45 ft³ for a 60 lb bag of QUIKRETE Concrete Mix, and about 0.014 m³ for a 30 kg bag of SAKRETE Concrete Mix sold in Canada. You cannot buy part of a bag, so the calculator always rounds up. Unit conversions use the exact factors in NIST SP 811.
Sources
Frequently asked questions
How many 80 lb bags of concrete are in a cubic yard?
It takes 45 bags of 80 lb concrete mix to make one cubic yard. Quikrete rates an 80 lb bag at about 0.60 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.60 = 45. With 60 lb bags (about 0.45 cubic feet each) you need 60 bags.
How much concrete do I need for a 10x10 slab?
A 10 ft by 10 ft slab 4 inches thick needs about 1.23 cubic yards (33.3 cubic feet) of concrete. That is 56 bags of 80 lb mix or 75 bags of 60 lb mix. A thicker slab needs proportionally more, so enter your own thickness above.
How much area does one bag of concrete cover?
At 4 inches thick, an 80 lb bag covers about 1.8 square feet and a 60 lb bag covers about 1.35 square feet. Those figures come from the published yields of 0.60 and 0.45 cubic feet per bag. At 2 inches thick, each bag covers twice the area.
How do I calculate concrete for post holes?
Choose Round, enter the hole diameter in feet (1 ft for a 12 inch hole) and the depth in inches, then set How many to the number of holes. The calculator gives the volume of the empty holes. The post itself takes up some of that space, so you will need slightly less.
How many 30 kg bags of concrete make a cubic meter?
About 72 bags. Sakrete rates a 30 kg bag of its concrete mix at approximately 0.014 cubic meters, and 1 ÷ 0.014 = 71.4, which rounds up to 72 whole bags. Switch the calculator to Metric to get 30 kg bag counts for your project.
Should I order extra concrete?
Usually, yes. Forms can bow, the ground under a slab is rarely perfectly flat, and some concrete is always lost while mixing and placing it. Use the Extra for waste field under Advanced options to add the allowance your supplier or contractor recommends.
Bag counts use the manufacturers' approximate yields. Other brands and mixes yield different amounts, so check the bag before you buy.