How to use the cubic yard calculator
- Choose the shape. Slab or bed is for anything with straight sides: a patio, a path, a shed base, a raised bed or a mulch border. Round hole is for post holes, footings dug with an auger and round columns poured in a tube form.
- Enter the measurements in feet and inches. For a 4 inch slab, put 0 in feet and 4 in inches. For a hole that is 2 ft 6 in deep, put 2 and 6.
- Set How many if you have several identical pieces, such as 10 fence post holes.
- Optional: add an extra percentage for waste, and the bag size of the mulch, soil or gravel you plan to buy.
The result shows cubic yards, cubic feet and cubic meters, and how many 80, 60 or 40 lb bags of premixed concrete give that volume. Copy result gives you the sizes and totals to paste into a note or an order.
How cubic yards are worked out
Every measurement is first turned into feet (inches divided by 12). Then:
- Slab or bed: length x width x depth = cubic feet.
- Round hole or column: 3.14159 x diameter x diameter / 4 x depth = cubic feet.
A cubic yard is a cube 3 feet on each side, so it holds 3 x 3 x 3 = 27 cubic feet. NIST's tables of units put it plainly: "27 cubic feet = 1 cubic yard". Divide cubic feet by 27 to get cubic yards.
For cubic meters, the calculator uses the exact definition of the foot, 0.3048 m, so one cubic foot is 0.3048 x 0.3048 x 0.3048 = 0.028316846592 cubic meters, and one cubic yard is about 0.7646 cubic meters.
Example: a 10 ft by 10 ft patio, 4 inches thick (press Try an example).
| Step | Working | Result |
|---|---|---|
| Depth in feet | 4 / 12 | 0.333 ft |
| Cubic feet | 10 x 10 x 0.333 | 33.33 cu ft |
| Cubic yards | 33.33 / 27 | 1.23 cu yd |
| Cubic meters | 33.33 x 0.0283168 | 0.94 m³ |
| With 10% extra | 33.33 x 1.10 | 36.67 cu ft, 1.36 cu yd |
How many bags of concrete
The bag counts use the yields that QUIKRETE prints for its Concrete Mix (No. 1101) on the product data sheet on its own website:
"A 40 lb (18.1 kg) bag yields approximately 0.30 ft3 (8.5 L)" ... "A 60 lb (27.2 kg) bag yields approximately 0.45 ft3 (12.7 L)" ... "An 80 lb (36.2 kg) bag yields approximately 0.60 ft3 (17 L)"QUIKRETE Concrete Mix data sheet
So the number of bags is the cubic feet divided by the yield of one bag, rounded up to a whole bag, because a store sells whole bags and a slab that is a few shovels short cannot be finished. For the 10 ft by 10 ft slab with 10% extra:
| Bag | Yield | Working | Bags |
|---|---|---|---|
| 80 lb | 0.60 cu ft | 36.67 / 0.60 = 61.1 | 62 |
| 60 lb | 0.45 cu ft | 36.67 / 0.45 = 81.5 | 82 |
| 40 lb | 0.30 cu ft | 36.67 / 0.30 = 122.2 | 123 |
If the division comes out exactly, nothing is added: 6 cubic feet is exactly 10 bags of 80 lb. Other mixes and other brands can yield a different amount, so check the yield printed on the bag you buy, and enter it under Bag size of your product if it differs. QUIKRETE also says this mix "is designed for pouring concrete 2 in (50 mm) thick or more", and the calculator reminds you if your slab is thinner.
For a large slab or a driveway, many people order ready-mixed concrete by the cubic yard from a local supplier instead. Ask how they round orders.
Post holes and round footings
Choose Round hole and enter the hole's width across and its depth. For 10 fence post holes, each 10 inches across and 2 ft 6 in deep:
| Step | Working | Result |
|---|---|---|
| One hole | 3.14159 x 10/12 x 10/12 / 4 x 2.5 | 1.36 cu ft |
| 10 holes | 1.3635 x 10 | 13.64 cu ft, 0.51 cu yd |
| 80 lb bags | 13.64 / 0.60 = 22.7 | 23 |
The calculator does not take off the space the post fills, so the figure is a little more than you need. QUIKRETE's guidance is to dig each hole "about 3 times the diameter of the post". Bags are counted for all the holes together, since a part bag left from one hole can go into the next.
Gravel, soil and mulch
Loose material works the same way. For a garden bed 20 ft long and 4 ft wide with 3 inches of mulch, that is 20 x 4 x 0.25 = 20 cubic feet, or 0.74 cubic yards.
Bagged mulch and soil show the volume of the bag on the front. Enter it under Bag size of your product (in cubic feet, or in liters when you measure in meters) and the calculator rounds the number of bags up. If the bag in this example says 2 cubic feet, you need 10 bags.
Gravel and stone are often sold by weight rather than volume. The weight of a cubic yard depends on the stone, its size and how wet it is, so this calculator does not guess it. Give the supplier the cubic yards and ask them to convert for the material you choose.
Measuring in meters
Choose Meters and enter meters and centimeters. A slab 3 m by 3 m and 10 cm thick is 3 x 3 x 0.10 = 0.90 m³, which is 31.78 cubic feet or 1.18 cubic yards. Concrete bags sold in other countries differ, so enter the yield in liters printed on your bag in the bag size box.
Questions and answers
How do I calculate cubic yards?
Multiply length x width x depth, all in feet, to get cubic feet, then divide by 27. A 10 ft by 10 ft slab 4 inches thick is 10 x 10 x 0.333 = 33.33 cubic feet, or 1.23 cubic yards.
How many 80 lb bags of concrete make a cubic yard?
QUIKRETE states that an 80 lb bag of its Concrete Mix yields about 0.60 cubic feet. A cubic yard is 27 cubic feet, and 27 / 0.60 = 45, so 45 bags. With 60 lb bags (0.45 cu ft) it is 60 bags, and with 40 lb bags (0.30 cu ft) it is 90.
Why does the calculator round bags up?
Stores sell whole bags, and being short in the middle of a pour is worse than having part of a bag left. Any fraction of a bag counts as one more bag.
Should I add extra for waste?
Many people add 5 to 10 percent for an uneven base, spills and forms that bow out. That is a common allowance, not a rule. Enter your own figure under Extra for waste.
How thick should a concrete slab be?
That depends on what it carries and on your local building code. The calculator only works out the volume. QUIKRETE says its Concrete Mix is designed for pours 2 inches (50 mm) thick or more.
How many cubic feet are in a cubic yard?
Exactly 27, because a yard is 3 feet and 3 x 3 x 3 = 27.
Sources
Checked on 7 October 2026. If a rule has changed, please tell us.