Concrete Calculator
Tells you exactly how many yards or bags to buy.
Sources checked 8 November 2026
Concrete calculator
How to calculate concrete volume: feet and inches to cubic yards
Concrete is sold by the cubic yard, and a yard is 27 cubic feet. So the whole job is: turn every size into feet, multiply them for cubic feet, divide by 27 to convert cubic feet to cubic yards, then add a little extra for spillage, uneven ground and forms that bow. Below are the steps for the sizes in the calculator above; they update as you type.
Read the tape into feet
10′ 0″ = 10 ft. 10′ 0″ = 10 ft. 4″ = 4 ÷ 12 = 0.333 ft.
Multiply for cubic feet
10.00 × 10.00 × 0.333 = 33.33 cu ft
Divide by 27 for cubic yards
33.33 ÷ 27 = 1.23 cu yd
Add the extra
1.23 × 1.10 = 1.36 cu yd. That is the number to order.
Bags: divide by the yield, round up
36.67 cu ft ÷ 0.60 = 61.1, so 62 bags of 80 lb.
Cubic yards = length × width × thickness ÷ 27 × (1 + extra)
10.00 × 10.00 × 0.333 = 33.33 cu ft; ÷ 27 = 1.23 cu yd; × 1.10 = 1.36 cu yd
All sizes in feet. Extra is 10% unless you change it.
If you already know the area in square feet, skip the first multiplication: square feet × thickness in feet ÷ 27 gives cubic yards. The square footage calculator works out the area of any shape. A 4 in slab is 0.333 ft thick, so 100 sq ft at 4 in is 33.33 cu ft, or 1.23 cu yd before the extra.
People often ask for a cement calculator when they mean concrete. Cement is one ingredient of the mix; the bags and the truck sell concrete, and that is what this page counts.
Formulas for footings, walls, round columns and steps
Every shape is the same three steps; only the multiplication changes. Sizes are in feet, and each example uses 10% extra.
Footing
Length × width × depth. A footing 20 ft long, 2 ft wide and 1 ft deep holds 40.00 cu ft, or 1.48 cu yd. With the extra, order 1.63 cu yd or 74 bags of 80 lb.
Wall
Length × height × thickness. A wall 20 ft long, 8 ft high and 8 in thick (0.667 ft) holds 106.67 cu ft, or 3.95 cu yd. Order 4.35 cu yd with the extra.
Round column or post hole
3.1416 × (diameter ÷ 2)² × height × number of columns. Four tubes 12 in across and 4 ft high hold 12.57 cu ft, or 0.47 cu yd: 24 bags of 80 lb with the extra.
Steps
Solid steps poured on the ground are a stack of blocks: the bottom step is one rise tall, the second two rises, and so on. So the volume is width × run × rise × (1 + 2 + … + number of steps). Four steps with a 7 in rise, an 11 in run and a 3 ft width hold 16.04 cu ft, or 0.59 cu yd. A formula that multiplies by one rise per step counts 4 rises here instead of 10, and comes up short.
How many square feet a yard of concrete covers
One cubic yard spread at 4 in covers 81 sq ft. Thicker pours cover less:
| Thickness | Sq ft per cu yd |
|---|---|
| 3.5 in | 92.6 |
| 4 in | 81 |
| 5 in | 64.8 |
| 6 in | 54 |
| 8 in | 40.5 |
Worked out: 27 cu ft ÷ (thickness in inches ÷ 12). No extra added.
Bag yield: 40, 60 and 80 lb
A bag's yield is the volume of concrete it makes once mixed. Divide the cubic feet you need by the yield and round up.
| Bag | Yield per bag | Bags for 1 cu yd | Bags on a pallet |
|---|---|---|---|
| 80 lb | 0.60 cu ft | 45 | 42 |
| 60 lb | 0.45 cu ft | 60 | 56 |
| 40 lb | 0.30 cu ft | 90 | 80 |
Yield: Quikrete and Sakrete data sheets. Pallets: Quikrete. Bags for a yard: 27 ÷ yield, before any extra.
Sakrete prints 45 bags of 80 lb to a yard, the same count the yield gives.
How thick to pour
The makers' project sheets and the residential code give these thicknesses. Your local code and the load on the slab come first.
| Job | Thickness | Source |
|---|---|---|
| Sidewalk | at least 4 in | Quikrete project sheet |
| Patio | 4 in | Quikrete project sheet |
| Driveway, cars | 4 in | Quikrete project sheet |
| Driveway, trucks or heavy vehicles | 5 to 6 in | Quikrete project sheet |
| Shed base | 4 to 6 in, by load | Quikrete project sheet |
| Garage floor | 4 in typical; 5 to 6 in for heavy vehicles | Quikrete project sheet |
| House floor slab, code | not less than 3 1/2 in | 2025 California Residential Code |
Quikrete 1101 and Sakrete High-Strength are rated for pours 2 in thick or more. For a thinner layer, use a topping or resurfacing mix.
Bags or a ready-mix truck
Bags come stacked on pallets: 42 bags of 80 lb, 56 of 60 lb or 80 of 40 lb to a pallet, so the shopping list above shows how many pallets and loose bags make up your count.
Ready-mix plants sell by the cubic yard, rounded up to 1/4 or 1/2 yd steps, so give the plant your estimate in cubic yards with the extra included. Ready-mix concrete typically comes in a truck mixer that carries 8 to 12 cu yd, and an order under 5 cu yd often carries a short-load charge.
Ready-mix concrete pricing is set by each plant, so this page counts the concrete, not the concrete cost. Ask the plant for its price per yard, its step, its minimum and that charge before you choose.
The extra matters most with a truck: running short in the middle of a pour means a cold joint or a second delivery. NRMCA advises ordering 4 to 10% over the plan volume; the calculator starts at 10%, Sakrete's figure.
Concrete calculator FAQ
How much concrete do I need?
To find how much concrete you need, multiply length × width × thickness in feet, divide by 27 for cubic yards, and add 4 to 10% extra. A 10 × 10 ft slab at 4 inches is 1.23 cu yd; with 10% extra, order 1.36 cu yd.
How many square feet does a yard of concrete cover?
92.6 sq ft at 3 1/2 in, 81 at 4 in, 64.8 at 5 in and 54 at 6 in, before any extra.
How many 80 lb bags make a yard?
45: each 80 lb bag makes 0.60 cu ft, and a yard is 27 cu ft. It takes 60 bags of 60 lb or 90 of 40 lb.
How many bags of concrete for a 10x10 slab?
At 4 in thick with 10% extra: 62 bags of 80 lb, 82 of 60 lb or 123 of 40 lb (1.36 cu yd).
Should I buy bags or ready-mix?
Compare the bag count, a pallet or more of heavy lifting and mixing, with what the plant charges for your yardage, its order step and any short-load charge under 5 cu yd. The shopping list above gives both sides.
How thick should a slab or driveway be?
Sidewalks and patios 4 in, a driveway for cars 4 in and one for trucks 5 to 6 in, per Quikrete's project sheets. The residential code asks for at least 3 1/2 in under a house floor. Bagged mix needs 2 in or more.
Related calculators
Sources
Every yield, pallet count, thickness and ordering figure on this page comes from these documents, checked 8 November 2026.
- Quikrete, Concrete Mix No. 1101 data sheet, revised October 2022
- Quikrete, Concrete Mix 1101 product page
- Sakrete, High-Strength Concrete Mix page and technical data sheet
- Sakrete, Estimating Bagged Concrete Jobs
- NRMCA, CIP 31 Ordering Ready Mixed Concrete
- NRMCA, CIP 8 Discrepancies in Yield
- Quikrete project sheet, Concrete Driveways and Curbs
- Quikrete project sheet, Concrete Sidewalks and Small Slabs
- Quikrete project sheet, Concrete Patios
- 2025 California Residential Code, section R506.1 (IRC based)
- Sonoco, Sonotube Round brochure
- Sonoco, Sonotube Concrete Forming Products brochure
- Jefferson County, Missouri, ready-mix bid tabulation, February 2020
- Grannas Bros., ready-mix calculator page
- Vertigraph, How to Calculate Concrete Yardage