How to use the concrete calculator
- Pick the shape. Choose slab, footing, wall, round column, square column, round pad, steps or curb and gutter.
- Enter the dimensions. Type each dimension and choose its unit. Every field has its own unit, so the length can be in feet while the thickness is in inches.
- Read the result. The result shows the cubic yards to order, the bags needed in each bag size and the weight. Add your own price to see a cost, then download the estimate as a PDF or share it on WhatsApp.
What is a concrete calculator?
A concrete calculator is a tool that turns the dimensions of a pour into a volume of concrete. It multiplies the dimensions, then converts the volume into the units concrete is sold in: cubic yards or cubic metres for ready-mix, and bags for pre-mixed concrete.
This online calculator covers eight shapes. It works out the concrete volume from the formula for each shape, adds a waste allowance, and gives the cubic yards, the square feet of a flat pour, the weight and, if you enter a price, an estimated cost.
Cement and concrete are not the same thing. Quikrete describes its Concrete Mix as a blend of portland cement, sand, and gravel or stone: cement is the binder inside concrete. A search for a cement calculator is usually a search for this kind of concrete calculator.
Features
- Eight shapes: slab, footing, wall, round column, square column, round pad, steps, and curb and gutter
- A live 3D preview with your dimensions on it, and a plan view, that redraw as you type
- A separate unit for every field: feet, inches, yards, metres, centimetres or millimetres
- Volume in cubic yards, cubic feet and cubic metres
- Bag counts for 40 lb, 50 lb, 60 lb and 80 lb bags
- Weight in pounds, short tons and kilograms
- An adjustable waste allowance and a quantity field for repeated pieces
- A cost estimate from your own price per cubic yard or per bag
- A one-page PDF of the estimate with the drawing, the inputs and every result
- A WhatsApp share button for the estimate
What you can use it for
- A patio, a shed base or a garage floor (slab)
- Footings under a wall, a deck or an addition (footing)
- A poured concrete wall or a foundation wall (wall)
- Piers and posts in round or square forms (round column, square column)
- A round pad for a hot tub, a fire pit or a grain bin (round pad)
- Front steps and back steps (steps)
- A curb and gutter along a drive or a street (curb and gutter)
Concrete formulas for each shape
Every formula gives a volume. Convert all dimensions to the same unit before you multiply. The calculator converts each field to feet, so the first answer is in cubic feet.
| Shape | Formula |
|---|---|
| Slab | Length × width × thickness |
| Footing | Length × width × depth |
| Wall | Length × height × thickness |
| Round column | π × (diameter ÷ 2)² × height |
| Square column | Width × depth × height |
| Round pad | π × (diameter ÷ 2)² × thickness |
| Steps | Width × rise × run × (1 + 2 + … + number of steps) |
| Curb and gutter | Length × ((curb depth + gutter width) × flag thickness + curb depth × curb height) |
To convert the result: 1 cubic yard = 27 cubic feet, and 1 cubic foot = 0.0283 cubic metres.
The steps formula is for solid steps, where the concrete under each step goes down to the ground. The curb formula treats the curb and gutter as two rectangles: a flat base under the whole width, and the curb standing on it.
Worked example: a 10 ft by 10 ft slab, 4 inches thick
These are the numbers the calculator shows when the page opens.
- Convert the thickness to feet: 4 in ÷ 12 = 0.333 ft.
- Multiply: 10 ft × 10 ft × 0.333 ft = 33.33 cubic feet.
- Convert to cubic yards: 33.33 ÷ 27 = 1.23 cubic yards.
- Add 10% waste: 33.33 × 1.10 = 36.67 cubic feet, which is 1.36 cubic yards or 1.04 cubic metres.
- In 80 lb bags: 36.67 ÷ 0.60 = 61.1, so 62 bags.
- Weight at 145 lb per cubic foot: 36.67 × 145 = about 5,317 lb, which is 2.66 short tons.
Bags of concrete per cubic yard
A bag of concrete mix is sold by its dry weight, but what matters is its yield: the volume of mixed concrete one bag makes. The bag count is the volume to order divided by the yield, rounded up to a full bag.
| Bag size | Yield per bag | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 cubic feet | 90 |
| 50 lb | 0.375 cubic feet | 72 |
| 60 lb | 0.45 cubic feet | 60 |
| 80 lb | 0.60 cubic feet | 45 |
The yields are the approximate values in the Quikrete Concrete Mix data sheet (product 1101, revised October 2022). Another mix can yield a different amount. The yield printed on the bag you buy is the one to trust.
How much concrete to order: the waste allowance
The waste allowance is extra concrete added to the exact volume. It covers ground that is not level, forms that bow, spills and concrete left in the mixer or the chute.
The calculator starts at 10%. Change it to fit your job: lower for a small, well-formed pour, higher for rough or hand-dug ground. Set it to 0 to see the exact volume.
The formula is: volume to order = exact volume × (1 + waste ÷ 100).
How much concrete weighs
The weight is the volume to order times the weight of one cubic foot of concrete. The calculator offers three values.
| Choice | Weight per cubic foot | Weight per cubic yard | Source |
|---|---|---|---|
| Normal-weight concrete | 145 lb | 3,915 lb | Federal Highway Administration report FHWA-HRT-05-057 |
| Reinforced concrete | 150 lb | 4,050 lb | The same report: reinforced concrete is generally taken as 5 lb per cubic foot more |
| Bagged concrete mix | 140 lb | 3,780 lb | Quikrete Concrete Mix data sheet (approximate unit weight) |
The weight of real concrete changes with the stone in the mix and the water content. The Federal Highway Administration figure applies to concrete up to 5,000 psi.
What the calculator includes
- Each dimension can be up to 10,000 in its unit. Quantity can be 1 to 1,000, steps 1 to 50 and waste 0 to 50%.
- The steps shape has no landing and assumes solid steps.
- The calculator handles one shape at a time. For an L-shaped slab, split it into rectangles, calculate each one and add the results.
- The calculator does not subtract door or window openings from a wall, or the post from a post hole.
- The preview is a drawing, not a scale plan. The labels always show the real dimensions, but a very small dimension is drawn thicker and a very long shape is shortened.
- A website cannot attach a file to a WhatsApp chat by itself. On a phone, the share button opens your share menu with the PDF, and you pick WhatsApp. On a browser that cannot share files, the PDF is downloaded and WhatsApp opens with the numbers as text.
Is it private?
Yes. The calculation runs in your browser, and the PDF is made in your browser too. The numbers you type are not sent to our server and are not saved. The site stores one thing on your device: your light or dark theme choice.
If you press the WhatsApp button, the estimate goes to WhatsApp or to your device's share menu. From that point WhatsApp handles it under its own privacy policy.
Tips for an accurate estimate
- Measure the formed area, not the plan: forms that bow out or a subgrade that dips add volume.
- Enter the thickness in inches and let the unit picker convert it. Mixing feet and inches is the most common mistake.
- Split an L-shaped or irregular pour into rectangles and circles, calculate each one, then add the results.
- Keep the waste allowance on. A short pour costs more than a little leftover concrete.
- For footings, walls and steps, check the size and strength your local building code requires before you order.
Built for every concrete and hardscape job
One site for the whole job, from the first measurement to the order.
For homeowners and DIY
- Bag counts by size for small pours
- A live 3D preview of the shape
- A PDF to take to the store
- A plain how-to on every page
For contractors
- Slabs, footings, walls, columns, steps and curbs
- A waste allowance you set
- Cost from your own price
- Share the estimate on WhatsApp
For landscapers
- Gravel, sand and pea gravel in tons and yards
- Pavers, paver base and polymeric sand
- Retaining wall blocks and drainage gravel
- Block, brick and mortar counts
For estimators
- Imperial and metric units in every field
- A named source for every figure
- Formulas with worked examples
- Rebar grid with weight and stock bars
- 21
- Calculators
- 17
- Published sources
- 2
- Languages
- 100%
- Free, no sign-up
Related calculators
Frequently asked questions
- How do I calculate cubic yards of concrete?
- Multiply the length, width and thickness in feet to get cubic feet, then divide by 27. For example, 10 ft × 10 ft × 0.333 ft is 33.33 cubic feet, which is 1.23 cubic yards.
- How much concrete do I need for a 10 x 10 slab?
- A 10 ft by 10 ft slab that is 4 inches thick needs 1.23 cubic yards, or 1.36 cubic yards with 10% waste. At 6 inches thick it needs 1.85 cubic yards before waste.
- How many 80 lb bags of concrete make a cubic yard?
- 45 bags. The Quikrete Concrete Mix data sheet gives a yield of about 0.60 cubic feet for an 80 lb bag, and a cubic yard is 27 cubic feet. For 60 lb bags the number is 60.
- How much does a cubic yard of concrete weigh?
- About 3,915 lb at 145 lb per cubic foot, the Federal Highway Administration figure for normal-weight concrete. At 150 lb per cubic foot, often used for reinforced concrete, it is 4,050 lb.
- How do I calculate concrete by the square foot?
- Multiply the area in square feet by the thickness in feet, then divide by 27 to get cubic yards. 100 square feet at 4 inches thick is 100 × 0.333 ÷ 27 = 1.23 cubic yards before waste.
- Is a cement calculator the same as a concrete calculator?
- Usually, yes. Cement is one ingredient of concrete, with sand, gravel and water. When people ask how much cement they need for a slab or a footing, they normally mean how much concrete, which is what this calculator works out.
- Can I mix feet, inches and metric units?
- Yes. Every field has its own unit. You can enter the length in feet, the thickness in inches or millimetres, and read the answer in cubic yards and cubic metres.
- Does the calculator know the price of concrete?
- No. Concrete prices change by place and by supplier, so the calculator has no built-in prices. Enter your own price per cubic yard or per bag to get a cost.
- Can I save or send the result?
- Yes. Download PDF saves a one-page estimate with the drawing, your dimensions and every result. Share on WhatsApp sends that PDF through your phone's share menu, or opens WhatsApp with the numbers as text when the browser cannot share files.
- Is the result exact?
- No. It is an estimate based on the dimensions you enter. Uneven ground, form movement and spills change the real amount, which is why the calculator adds a waste allowance.
Sources
Every figure this calculator uses comes from the published sources below. The formulas are on this page, so any result can be checked by hand.
- Quikrete, Concrete Mix No. 1101: data sheet and product page. Bag yields: 0.30 ft³ (40 lb), 0.375 ft³ (50 lb), 0.45 ft³ (60 lb) and 0.60 ft³ (80 lb); bags per pallet: 80, 56 and 42.
- Federal Highway Administration (FHWA), Report FHWA-HRT-05-057. Normal-weight concrete: 145 lb per cubic foot (1.96 tons per cubic yard).