Concrete guide
Plan your concrete project
Cubic feet, cubic yards and bags
Concrete is measured by volume. Convert the thickness from inches to feet by dividing by 12, multiply by the length and width, and you have cubic feet. Ready-mix suppliers sell by the cubic yard, which is 27 cubic feet.
Bagged mix is labeled with its yield. An 80 lb bag of standard concrete mix makes about 0.60 cu ft, so one cubic yard takes about 45 bags.
Bags or a truck?
Bags make sense for post holes, steps and small slabs. Past about one cubic yard, mixing by hand turns into a long day, and many people switch to a ready-mix delivery or a rented mixer. Check the minimum order and short-load fee with your local supplier.
Gravel is sold by weight
Quarries and landscape yards usually sell stone by the ton. The calculator works out the cubic yards, then converts to tons with a weight per cubic yard. Crushed stone is often around 1.4 tons per cubic yard, but the figure changes with the stone and its moisture, so use your supplier's number when you have it.
Bag yields and weights
| Item | Typical figure | Note |
|---|---|---|
| 80 lb bag of concrete mix | About 0.60 cu ft | 45 bags per cubic yard |
| 60 lb bag of concrete mix | About 0.45 cu ft | 60 bags per cubic yard |
| 40 lb bag of concrete mix | About 0.30 cu ft | 90 bags per cubic yard |
| One cubic yard at 4 in thick | About 81 sq ft | 27 cu ft ÷ 1/3 ft |
| Crushed stone | About 1.4 tons per cubic yard | Ask your supplier for their figure |
Common mistakes
- Entering the thickness in inches where feet are expected.
- Ordering the exact volume with nothing extra for spills and uneven ground.
- Assuming every bag of mix has the same yield.
- Ordering gravel by volume when the yard sells it by the ton.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
About 45. An 80 lb bag yields about 0.60 cu ft, and a cubic yard is 27 cu ft.
How thick should a concrete patio be?
Four inches is the common thickness for patios and walkways. Areas that carry vehicles are usually thicker; follow local code and your plans.
How much extra concrete should I order?
Adding about 10% covers spills, uneven ground and forms that bow slightly.
How many tons of gravel are in a cubic yard?
Most gravel and crushed stone weigh about 1.3 to 1.5 tons per cubic yard. Ask the supplier for the weight of the exact stone you are buying.
Sources
- Quikrete, Concrete Mix specification sheet
- Select Sand & Gravel, How Much Does a Yard of Crushed Stone Weigh?