Concrete Yard Calculator
This concrete yard calculator turns the measurements of a slab, footing, wall, column or round pad into cubic yards, with the extra allowance, cubic feet, cubic metres, weight, truckloads and bag count. Add up to six sections (as rectangles or circles) to calculate a whole project in one go, and the calculator adds them together. Tap the i button beside any field for an explanation.
A cubic yard is a cube 3 feet on each side, so it holds 27 cubic feet, or about 0.765 cubic metres. Everything on this page follows from that single fact.
Quick answer: cubic yards = length (ft) × width (ft) × depth (in) ÷ 324. A 12 × 20 ft slab that is 4 in thick holds 2.96 cubic yards. Add about 10% extra, which makes 3.26, and order 3.5 yards.
Calculate cubic yards of concrete
Example values are loaded so you can see a result straight away. Change any field and the numbers update.
1. Choose your units
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2. Describe what you are pouring
Add one section for each separate shape, such as a slab, a footing and some post holes. The calculator adds them together.
3. Extra allowance, price and bags
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Where the volume goes
If the depth is off
Concrete needed with extra if every section is deeper or shallower by the amount shown. Your measurement is the orange bar.
| Section | Volume | Share |
|---|---|---|
| Total with extra allowance | 100% |
Bags needed by size
Same concrete, different bag sizes. Your selected size is orange.
Truckload plan
Shown as full trucks first. Your plant may split the order evenly instead.
Estimates for planning only. Prices shown are examples you can edit, not quotes. Confirm measurements on site and follow your local building code. See our Disclaimer.
How to calculate yards of concrete
If you want to check the calculator by hand, or work out a quick figure on site, the method for any rectangular shape is four steps:
- Convert every measurement to feet. Divide inches by 12. A 4 in slab is 0.333 ft thick.
- Multiply length × width × depth to get cubic feet.
- Divide by 27 to get cubic yards.
- Add an allowance, usually 5% to 10%, and round up to the order size your supplier uses.
Worked example: a 12 × 20 ft slab, 4 in thick
The slab holds 12 × 20 × 0.333 = 80 cubic feet. Divided by 27, that is 2.96 cubic yards. Adding 10% gives 3.26 cubic yards, and a plant working in quarter-yard steps would take the order as 3.5 yards.
The 324 shortcut
When the depth is in inches, there is a faster way to figure yards of concrete: length in feet × width in feet × depth in inches ÷ 324. The number comes from 27 × 12, the two conversions folded into one. The same slab gives 12 × 20 × 4 ÷ 324 = 2.96, the same answer as the long method. It is easy to do on a phone calculator while standing in the yard.
Round shapes: columns, piers and round pads
For a circle, the area is 0.7854 × diameter × diameter. Multiply by the depth in feet and divide by 27. A 10 ft round pad that is 4 in thick holds 0.7854 × 10 × 10 × 0.333 ÷ 27 = 0.97 cubic yards. A single 12 in post hole that is 3 ft deep holds 0.7854 × 1 × 1 × 3 ÷ 27 = 0.09 cubic yards, which is why a set of deck footings adds up to far less than people fear.
Formulas for common shapes
Every shape below uses feet for all measurements. Convert inches first, then divide the result by 27 for cubic yards.
| Shape | Formula (feet) | Example | Result |
|---|---|---|---|
| Slab, patio or pad | length × width × depth ÷ 27 | 12 × 20 ft, 4 in thick | 2.96 yd³ |
| Footing or grade beam | run × width × depth ÷ 27 | 40 ft run, 16 in wide, 8 in deep | 1.32 yd³ |
| Wall | length × thickness × height ÷ 27 | 20 ft long, 8 in thick, 4 ft high | 1.98 yd³ |
| Round pad | 0.7854 × diameter² × depth ÷ 27 | 10 ft across, 4 in thick | 0.97 yd³ |
| Column, pier or post hole | 0.7854 × diameter² × depth ÷ 27 | 12 in across, 3 ft deep | 0.09 yd³ |
Footings and walls are where unit mistakes happen, because they are measured in two different units. A footing that is 16 in wide and 8 in deep is 1.33 ft by 0.67 ft. In the calculator you avoid the conversion by choosing feet for the run and typing the width in feet, then picking inches for the depth.
Calculating several pours at once
Real projects rarely have one shape. Take a small backyard job: a 12 × 16 ft patio that is 4 in thick, a 4 × 4 ft landing that is 6 in thick, and six round footings, each 10 in across and 36 in deep. Entered as three sections, the calculator gives:
- Patio: 2.37 cubic yards
- Landing: 0.30 cubic yards
- Six footings: 0.36 cubic yards
The total is 3.03 cubic yards. With 10% extra that is 3.33, ordered as 3.50 yards. Ordering one combined volume instead of three small ones also helps with price, because small orders often carry a minimum-load charge.
How far does a yard of concrete go?
This is the question behind the search for how much concrete you need for a given area. One cubic yard covers 324 divided by the thickness in inches, in square feet. At 4 in that is 81 square feet, and at 6 in it is 54.
| Thickness | Area covered by 1 cubic yard | Yards for 100 sq ft |
|---|---|---|
| 2 in | 162 sq ft | 0.62 yd³ |
| 3 in | 108 sq ft | 0.93 yd³ |
| 3.5 in | 92.6 sq ft | 1.08 yd³ |
| 4 in | 81 sq ft | 1.23 yd³ |
| 5 in | 64.8 sq ft | 1.54 yd³ |
| 6 in | 54 sq ft | 1.85 yd³ |
| 8 in | 40.5 sq ft | 2.47 yd³ |
| 12 in | 27 sq ft | 3.70 yd³ |
Use the table to sanity-check any quote or estimate. If someone tells you a 400 sq ft slab at 4 in needs 3 yards, 400 ÷ 81 shows it needs closer to 5.
Cubic yards for common projects
These figures show the order size for typical jobs, with 10% extra and rounding up to the next quarter yard.
| Project | Size and thickness | Cubic yards | Order (10% extra) |
|---|---|---|---|
| Shed pad | 8 × 10 ft, 4 in | 0.99 | 1.25 |
| Small patio | 12 × 12 ft, 4 in | 1.78 | 2.00 |
| Sidewalk | 3 × 40 ft, 4 in | 1.48 | 1.75 |
| Driveway | 12 × 40 ft, 5 in | 7.41 | 8.25 |
| Two-car garage floor | 24 × 24 ft, 5 in | 8.89 | 10.00 |
Treat these as starting points. Your own dimensions, thicker edges and uneven ground will move the numbers, which is what the calculator is for.
How much extra concrete should you order?
Adding 5% to 10% is the usual rule. The ground is never perfectly level, forms bow slightly under the weight of wet concrete, and some always stays in the chute and wheelbarrow. A pour that comes up short is a bigger problem than leftover concrete, because a second batch arriving late leaves a cold joint that is weaker and shows on the surface.
Use the low end, 5%, for a carefully prepared, level base with rigid forms. Use the high end, or a little more, for an irregular excavation, a thin slab spread over a large area, or a first-time pour. On a 4 in slab, an error of half an inch in the average depth is a 12.5% change in volume, which is why the calculator charts the effect of depth on your order.
How many bags of concrete are in a yard?
For small jobs such as a post footing, a set of steps or a small pad, bagged mix is practical. The yield is printed on each bag, and the usual figures are in the table. They give the number of bags in one cubic yard and the weight of dry mix you would handle.
| Bag size | Typical yield (cu ft) | Bags per cubic yard | Dry mix per cubic yard |
|---|---|---|---|
| 40 lb bag | 0.30 | 90 | 3,600 lb |
| 50 lb bag | 0.375 | 72 | 3,600 lb |
| 60 lb bag | 0.45 | 60 | 3,600 lb |
| 80 lb bag | 0.6 | 45 | 3,600 lb |
The weight of dry mix for a yard (3,600 lb) is lower than the weight of the poured concrete (about 4,000 lb), because the rest is the water you add. Check the yield on the brand you buy, since it can differ slightly between manufacturers.
For your own numbers, our concrete bag calculator shows the bag count for every size, and handles fence post holes and round columns too. Past about 1 cubic yard, a truck is almost always the more sensible choice.
How much does a yard of concrete weigh?
A cubic yard of normal-weight concrete weighs roughly 4,000 pounds, a little over two tons. The calculator uses 150 pounds per cubic foot, a common planning figure, which comes to 4,050 pounds per yard. In metric terms that is about 2,400 kilograms per cubic metre, or 1,837 kilograms per cubic yard.
The weight matters before the pour as much as after it. A fully loaded mixer truck is very heavy, so ask the plant whether the delivery route and your driveway, lawn, septic cover or pavers can carry it. If not, a pump truck or a shorter chute may be needed, and either can add to the bill.
Cubic yards, cubic feet and cubic metres
The calculator reports your volume in more than one unit, since suppliers and plans do not always agree. These are the conversions it uses.
| Starting volume | In cubic feet or yards | In cubic metres | In litres |
|---|---|---|---|
| 1 cubic yard | 27 cubic feet | 0.7646 cubic metres | 764.6 litres |
| 1 cubic foot | 0.0370 cubic yards | 0.0283 cubic metres | 28.32 litres |
| 1 cubic metre | 1.308 cubic yards | 35.31 cubic feet | 1,000 litres |
If your supplier quotes in cubic metres and you measured in feet, switch the calculator to metric, or multiply cubic yards by 0.7646. Conversion factors like these are published by the National Institute of Standards and Technology.
How much is a yard of concrete?
Ready-mix is priced per cubic yard, and the price depends on the strength of the mix, how far the truck travels, the season and the local market. Small orders often add a short-load or minimum-delivery charge. Ask two or three plants for the price per yard, the delivery fee and the minimum load, then enter them in the calculator above for a quick estimate of the concrete bill.
For the full cost of a slab, including the gravel base, reinforcement and labour, use our concrete slab cost calculator, which prices each of those separately and compares ready-mix with bagged mix.
Ordering from a ready-mix plant
Once you know the yards, the order itself is a short conversation. Have these details ready:
- Volume. Give the rounded figure from the calculator, including the allowance.
- What you are pouring. A patio, a footing and a driveway can call for different mixes, so describe the job and let the plant recommend one.
- Access. Tell them about gates, slopes, soft ground and overhead wires, and how close the truck can get.
- Timing. Ready-mix has a limited window, often about 90 minutes from batching, before it must be discharged, so have forms, base, helpers and finishing tools ready before the truck arrives.
A full mixer carries roughly 10 cubic yards at most, and many plants load less, so a large order becomes several trucks. The truckload chart in the results shows how your order would split.
Common mistakes when figuring yards of concrete
- Mixing units. Feet for length and inches for depth is the classic error. Convert before multiplying, or use the 324 shortcut.
- Using the wrong diameter. A post hole is wider than the post. Measure the hole, not the post.
- Forgetting the thicker edges. Many slabs have a thicker perimeter or footing. Enter it as its own section.
- Measuring depth once. Check it at the corners and the middle. Low spots swallow concrete.
This page is for planning only. For structural slabs, heavy loads or poor soil, ask a professional to specify the work.
Concrete yard calculator FAQ
How do I calculate yards of concrete?
Multiply length, width and depth in feet to get cubic feet, then divide by 27. If the depth is in inches, you can use the shortcut length (ft) × width (ft) × depth (in) ÷ 324. Add 5% to 10% extra and round up to the order size your supplier uses.
How many yards of concrete do I need for a 10 × 10 slab?
A 10 × 10 ft slab that is 4 inches thick holds 1.23 cubic yards. With 10% extra that is 1.36, which you would order as 1.50 yards. At 6 inches thick it holds 1.85 cubic yards before any extra.
How many bags of concrete make a yard?
One cubic yard needs about 45 bags of 80 lb mix, 60 bags of 60 lb mix, 72 bags of 50 lb mix or 90 bags of 40 lb mix, based on the common yields of 0.60, 0.45, 0.375 and 0.30 cubic feet per bag. Always check the yield printed on the bag you buy.
How much does a yard of concrete weigh?
About 4,000 pounds, a little over two tons. This calculator uses 150 lb per cubic foot, which is 4,050 lb per cubic yard, or roughly 1,837 kg.
How do I calculate yards of concrete for a round column or post hole?
Find the area of the circle with 0.7854 × diameter × diameter, using feet. Multiply by the depth in feet and divide by 27. A 12 in wide, 3 ft deep hole needs about 0.09 cubic yards, or 2.4 cubic feet.
How much extra concrete should I order?
Most people add 5% to 10% for uneven ground, spillage and forms that flex, then round up to the next quarter yard. A pour that runs short is a bigger problem than a small amount left over.
How much is a yard of concrete?
The price depends on your local plant, the mix, the delivery distance and the season, so call two or three suppliers. Our concrete slab cost calculator lets you enter the price per yard and see the full cost of a slab.
Can I use this calculator for walls, footings and driveways?
Yes. Choose rectangle for walls, footings, steps and driveways, and circle for columns, piers and round pads. Add one section for each shape, and the calculator adds the volumes together.
Sources and further reading
The volume formulas are standard geometry, and a cubic yard is exactly 27 cubic feet. Normal-weight concrete is taken as 150 lb per cubic foot, a common planning figure. For product details and industry guidance, go to the source:
- NIST Special Publication 811, Guide for the Use of the International System of Units (unit conversion factors)
- QUIKRETE Concrete Mix (bag sizes, with the data sheet for yield)
- National Ready Mixed Concrete Association (industry guidance on ready-mixed concrete)
- American Cement Association (cement and concrete research and education)
Codes are adopted locally and change over time, so confirm the rules with your local building department.
Plan the rest of the project
If you are building a wall instead of pouring one, the concrete block calculator counts the blocks you need. To measure an odd-shaped area, use the square footage calculator, and browse the concrete calculators hub for more tools like this one.