A concrete calculator is a free tool that turns the dimensions of a pour into the material it needs, such as cubic yards of ready-mix, bags of concrete, weight and cost. GeniesMag brings these tools together in one place, grouped by the job you are doing, so you can size a slab, a footing, a column or a whole driveway in seconds.
Every calculator here is free, needs no sign-up, and runs entirely in your browser, so nothing you enter is stored. Each one shows the exact formula it uses and the primary sources behind its numbers, such as bag yields and unit weights, reviewed by Prof. Dr. Khalil Mudassar, PhD. Pick a category below, jump to a popular tool, or read how concrete is calculated further down the page.
Concrete Calculators by Category
The concrete tools are organised into four areas that follow a real project, from working out how much to order, to pouring flatwork, to foundations and structural elements. Open a category to see every calculator in it.
Most-Used Concrete Calculators
These are the tools people reach for first, whatever the project.
How to Calculate Concrete
Concrete is sold by volume, so every estimate starts by working out the space the pour will fill and converting it to cubic yards. For a rectangular slab or footing the volume is length times width times thickness, with every dimension in the same unit.
Because concrete is priced by the cubic yard and one cubic yard is 27 cubic feet, the concrete calculator works in feet, finds the cubic feet, and divides by 27. Thickness is usually given in inches, so it is divided by 12 first; a 4 inch slab is 0.333 feet thick. A waste allowance covers an uneven sub-base, spillage and over-excavation, so you do not run short mid-pour.
Round shapes use the area of a circle instead. A column or a sonotube pier is pi times the radius squared times the height, and the concrete column calculator handles both round and square sections.
A worked example
Say you are pouring a patio slab 12 feet long, 12 feet wide and 4 inches thick. First convert the thickness to feet: 4 divided by 12 is 0.333 feet. The volume is 12 times 12 times 0.333, which is 48 cubic feet. Divide by 27 and that is 1.78 cubic yards. Adding a 10 percent waste allowance brings it to about 1.96 cubic yards, roughly 88 eighty-pound bags, which is exactly the point where a short-load ready-mix delivery starts to beat mixing by hand. The concrete slab calculator runs this for your own dimensions and shows the bags, weight and area too.
Bags or ready-mix?
Small pours are mixed from bags; larger ones are delivered as ready-mix by the truck. A standard 80 pound bag of concrete mix yields about 0.60 cubic feet, so it takes roughly 45 bags to make a single cubic yard. That is why most jobs past one to two cubic yards are easier and cheaper as ready-mix. The concrete bag calculator gives a bag count for a small pour, and the bagged vs ready-mix calculator compares the two for your volume.
How thick should the concrete be?
Thickness drives the whole estimate, because it multiplies the entire area. Flatwork is commonly 4 inches thick for patios and walkways, and 5 to 6 inches for driveways and garage floors that carry vehicles. These are common figures, not a specification; the thickness a load-bearing slab needs comes from your plans, local code or an engineer. The concrete slab calculator turns whatever thickness you enter into the volume to order.
Planning a Concrete Pour
Most concrete projects follow the same four steps, and there is a tool for each one.
- Size the pour. Work out the volume in cubic yards from the length, width and thickness, and add a waste allowance. Start with the concrete calculator or a shape-specific tool such as the footing or stairs calculator.
- Reinforce it. Decide the rebar grid or wire mesh, then count the steel with the rebar calculator or wire mesh calculator.
- Order and deliver. Decide between bags and ready-mix, then plan the delivery with the truck calculator and, if access is tight, the pump cost calculator.
- Finish and cure. Place control joints and let the concrete cure, checking the strength gain with the curing time calculator and the joint spacing with the control joint calculator.
The category hubs above group every tool by the stage of the job, so you can move from one step to the next without hunting for the right calculator.
How Much Does Concrete Cost?
The cost of a pour is the concrete plus everything around it: delivery, any short-load fee for a part truck, a pump if the truck cannot reach, reinforcement, labour and finishing. Prices vary by region, mix strength, delivery distance and the size of the order, so the tools price a job from the figures you enter rather than quoting a single national number.
Three things move the price most: the volume, which sets how much concrete and how many truck loads you need; the mix, since a higher-strength concrete costs more per yard; and access, because a part-load short fee or a pump can add a fixed cost on top of the concrete itself. Working the volume out accurately first is what keeps the rest of the estimate honest.
Start with the volume, then price it: the concrete cost calculator totals a pour by the yard with delivery and short-load fees, the concrete slab cost calculator splits a slab into material, labour and finishing, and the concrete driveway cost calculator adds the gravel base and reinforcement. For delivery logistics, the concrete truck calculator works out how many loads you need and the concrete pump cost calculator budgets a pump.
Concrete Basics
A few terms come up across every concrete estimate. Each one has a tool that works with it.
Portland cement and the mix
Concrete is a mix of Portland cement, sand, gravel and water. The cement is the binder; the sand and gravel are the aggregate. The proportions are written as a ratio such as 1:2:3 (cement : sand : gravel). The concrete mix calculator splits a volume into those parts, and the cement calculator works out the bags of Portland cement.
Water-cement ratio and strength
The water-cement ratio, the weight of water divided by the weight of cement, largely sets how strong the hardened concrete will be: less water, within reason, means higher strength. Strength is quoted in pounds per square inch, such as 3,000 or 4,000 psi. The water cement ratio calculator sizes the mix water, and the compressive strength calculator turns a cylinder break into psi.
Weight and the cubic yard
Normal-weight concrete weighs about 150 pounds per cubic foot, so one cubic yard, at 27 cubic feet, weighs roughly 4,050 pounds, close to two short tons. The concrete weight calculator gives the weight of any volume, which matters for access, the sub-base and truck loads.
Rebar and reinforcement
Concrete is strong in compression but weak in tension, so slabs and footings are reinforced with steel: reinforcing bar, or rebar, in a grid, or welded wire mesh. The concrete rebar calculator counts the bars for a grid, the rebar weight calculator gives their weight, and the wire mesh calculator sizes welded sheets.
Curing and strength over time
Concrete gains strength through a chemical reaction that continues for weeks, fast at first and then slowly. On the standard ACI 209 curve, moist-cured concrete reaches about 70 percent of its 28-day strength at 7 days. The concrete curing time calculator estimates the strength at any age, and the control joint spacing calculator places the saw cuts that stop a slab cracking as it cures.
Common Mistakes When Estimating Concrete
A few errors come up again and again. The calculators guard against them, but they are worth knowing.
Mixing up feet and inches
Thickness is usually measured in inches but the volume formula works in feet, so a 4 inch slab is 0.333 feet, not 4. Entering the thickness in the wrong unit shrinks the result twelvefold. Keep length and width in feet and thickness in inches, as every tool labels its fields.
Forgetting the waste allowance
The raw geometry assumes a perfectly level base and no spillage. Real pours lose concrete to an uneven sub-base, the forms and the barrow, so ordering the exact calculated volume leaves you short. A 5 to 10 percent allowance covers it, and running short mid-pour risks a cold joint.
Counting bags by weight instead of volume
Bags are sold by weight but cover by volume. An 80 pound bag yields only about 0.60 cubic feet, so it takes roughly 45 of them to make one cubic yard. Judging coverage by the weight on the bag badly overestimates how far a pallet will go. The concrete bag calculator works it out by volume.
Frequently Asked Questions
How much concrete do I need?
Multiply length by width by thickness, with every dimension in feet, then divide by 27 for cubic yards and add 5 to 10 percent for waste. A 10 by 10 foot slab at 4 inches thick is about 1.23 cubic yards before waste. The concrete calculator does this for any shape.
How many bags of concrete are in a cubic yard?
About 45 eighty-pound bags, since one bag yields roughly 0.60 cubic feet and a cubic yard is 27 cubic feet. It is about 60 sixty-pound bags or 90 forty-pound bags. Past one to two cubic yards, ready-mix is usually easier than bags.
How much does a yard of concrete weigh?
Around 4,050 pounds, or close to two short tons, for normal-weight concrete at about 150 pounds per cubic foot. The concrete weight calculator gives the weight of your exact volume.
How thick should a concrete slab be?
Commonly 4 inches for patios and walkways, and 5 to 6 inches for driveways and garage floors that carry vehicles. The required thickness for a load-bearing slab comes from your plans or local code; the tools estimate the concrete, not the thickness.
How much does concrete cost?
It depends on the mix, the region, the delivery and the size of the order, so there is no single price. Size the pour first, then price it with the concrete cost calculator, which includes delivery and short-load fees.
Is it cheaper to use bags or ready-mix?
For a small pour under about a cubic yard, bags can be cheaper and simpler. Past one to two cubic yards, ready-mix usually wins on both cost and effort, because that much concrete is dozens of bags to mix by hand. The bagged vs ready-mix calculator compares them for your job.
How long does concrete take to cure?
Concrete keeps gaining strength for weeks. On the ACI 209 curve, moist-cured concrete is near 70 percent of its 28-day strength at 7 days, and close to full strength at 28 days. The curing time calculator estimates the strength at any age.
How much concrete does a 24 by 24 foot garage floor need?
A 24 by 24 foot slab at 4 inches thick is about 7.1 cubic yards before waste, or close to 7.8 with a 10 percent allowance. At 6 inches, for a floor that parks heavy vehicles, it is about 10.7 cubic yards. The garage floor calculator adds a thickened perimeter edge.
How many trucks will my pour need?
That depends on the load size your supplier delivers, which varies, so ask them before you order. Once you know it, the concrete truck calculator divides your volume by that load size, rounds up, and works out how to space the trucks so the concrete does not set between them.
Do the calculators show metric results?
Some do. A number of the tools show results in cubic meters, kilograms or metric tons next to the imperial figures, but not every calculator offers metric yet, so check the results of the tool you are using.
Do the calculators store my data?
No. Every calculation runs in your browser, there is no sign-up, and nothing you enter is stored or sent anywhere.
Ready to start? Browse the four concrete categories or open the concrete calculator to size your pour now.