Concrete Calculator

Measurement system:

Switch between imperial and metric units; existing values convert when you change systems.

Pour type:

The calculator changes dimension labels and formulas to match the selected pour.

Identical pours:

Use 1 for a single pour; enter a whole number for repeated matching sections.

pours

Hole or pier diameter:

Enter one round section diameter; identical pours multiplies it.

{{ depthLabel }}:

Concrete volume:

Enter one pour volume; identical pours multiplies it before waste.

Waste allowance: {{ formatNumber(waste_percent, 0) }}%

Use 5-15% for many field estimates; confirm with the supplier or installer before ordering.

Ready-mix rounding:

Quarter-yard rounding is a practical quote-check default; choose Exact for pure volume math.

Selected bag size:

Choose the bag size you expect to buy; yields are approximate and should be checked on the bag label.

Check concrete inputs

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Selected bag price:

Used only for the selected bag row and bag-vs-ready-mix cost comparison.

$ per bag

Ready-mix price:

Applied to the rounded ready-mix ticket, before delivery, short-load, pump, tax, or labor charges.

$ /yd3

Concrete density:

Leave 0 to omit the weight estimate; use a supplier or mix-design value when known.

Metric	Estimate	Order note	Copy
Enter valid concrete dimensions to build the takeoff table.
{{ row.metric }}	{{ row.estimate }}	{{ row.note }}

Mix size	Bags to buy	Yield and rounding note	Copy
Enter valid concrete dimensions to compare bag counts.
{{ row.mixSize }}	{{ row.bagsDisplay }}	{{ row.note }}

Check	Status	Detail	Copy
Enter valid concrete dimensions to show pour guidance.
{{ row.check }}	{{ row.status }}	{{ row.detail }}

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Concrete volume is a field-measurement problem before it becomes a buying problem. A slab, footing, trench, pier, or post hole must be reduced to a volume, then adjusted for repeated pours, uneven ground, form variation, spillage, and supplier ordering rules.

The main unit for ready-mix ordering in the United States is the cubic yard. Metric projects usually speak in cubic meters. Bagged concrete is different because each bag has an approximate mixed yield in cubic feet or liters, so the same pour can look small as a ready-mix ticket and still become a large number of bags.

The useful estimate separates the measured shape from the ordering margin. A 12 ft by 10 ft slab at 4 in thick is about 1.48 yd3 before extra allowance. Adding 10% raises the amount to about 1.63 yd3, and a supplier ticket rounded up to the nearest quarter yard becomes 1.75 yd3. That difference is not a math error. It is the practical gap between volume, buffer, and purchase increment.

A volume estimate does not verify structural design, reinforcement, sub-base preparation, drainage, local code, concrete strength, slump, curing, delivery access, or placement rate. It gives a clear quantity starting point so those checks can happen before ordering material.

Technical Details:

Concrete takeoff math is governed by geometry and unit conversion. Rectangular pours use plan area times thickness or depth. Round piers use circle area times filled depth. A known-volume takeoff skips the shape math and starts from the supplied volume. Repeated matching pours multiply the base volume before any allowance is added.

Waste allowance is a percentage added to the base volume. Industry ordering guidance commonly treats a small contingency as part of a sound ready-mix order because plan dimensions rarely capture every low spot, irregular excavation edge, form movement, or cleanup need. The calculator lets the allowance range from 0% to 40%, with guidance status changing below 5%, from 5% to 15%, and above 15%.

Concrete takeoff flow from measured shape through base volume to waste allowance, ticket rounding, and bag counts. — The same measured volume can lead to different purchase quantities once waste allowance, ready-mix ticket rounding, and bag yields are applied.

Formula Core:

The core calculation uses meters internally, then displays cubic meters, cubic feet, and cubic yards. The same equations apply to imperial and metric inputs after conversion.

\begin{matrix} V_{rect} & = & L \times W \times D \times N \\ V_{round} & = & π \times {(\frac{d}{2})}^{2} \times H \times N \\ V_{final} & = & V_{base} \times (1 + \frac{R}{100}) \\ B_{bags} & = & ⌈ \frac{V_{final ft3}}{Y} ⌉ \end{matrix}

Concrete takeoff symbols and meanings
Symbol	Meaning	Result field affected
L, W, and D	Rectangular length, width, and slab thickness or footing depth after unit conversion.	Base concrete volume
d and H	Round pier or post-hole diameter and filled depth.	Total footprint area and Base concrete volume
N	Identical pours, rounded to at least one whole matching section.	Pour type row and all volume rows
R	Waste allowance percent, limited to 0% through 40%.	Waste allowance volume and Final concrete volume
Y	Mixed yield per bag in cubic feet.	Bag Order rows and Bag Count Comparison

Bag counts are rounded up because a partial bag cannot be purchased as a usable fraction. The built-in bag yields are approximate mixed volumes, so the product label should take priority when a specific mix lists a different yield.

Bag yields used by the concrete calculator
Bag size	Yield used	How the row is used
40 lb / 18.1 kg	0.300 cu ft	Small-bag comparison row.
50 lb / 22.7 kg	0.375 cu ft	Middle-bag comparison row.
60 lb / 27.2 kg	0.450 cu ft	Common hand-mix comparison row.
80 lb / 36.3 kg	0.600 cu ft	Default selected-bag row and larger bag comparison.

Ready-mix rounding is applied to the final cubic-yard volume. Exact mode keeps the calculated amount. Quarter-yard, half-yard, and whole-yard modes round upward, then report the extra volume created by that ticket increment.

Concrete guidance thresholds
Result cue	Rule used	Meaning
Bag-friendly	Final volume is less than 0.5 yd3.	Bagged mix is likely practical for many small jobs.
Small pour	Final volume is at least 0.5 yd3 and less than 1 yd3.	Compare bag labor with a small ready-mix quote.
Crossover	Final volume is at least 1 yd3 and no more than 2 yd3.	Both bag labor and ready-mix dispatch need a cost and logistics check.
Ready-mix likely	Final volume is greater than 2 yd3.	Delivery is likely more practical for most crews.

Everyday Use & Decision Guide:

Set Measurement system first so the default units match the job. Use Imperial for feet, inches, and yd3. Use Metric for meters, centimeters, and m3. Switching systems converts current values, so check the displayed units before reading the result tables.

Choose the Pour type from the shape you measured. Slab or pad and Footing or trench use length, width, and depth. Round pier or post hole uses diameter and filled depth. Known volume is useful when a drawing, estimator, or supplier already gave you one volume and you only need waste, bag, ticket, and guidance checks.

Concrete Order Snapshot is the first sanity check. It shows the final volume, pour type, order lane, repeated pour count, selected bag count, and ready-mix ticket.
Concrete Takeoff is the main record view. It lists Total footprint area, Base concrete volume, Waste allowance volume, Final concrete volume, Ready-mix ticket, Selected bag order, optional cost, and optional weight.
Bag Order compares 40, 50, 60, and 80 lb bags using each bag yield and rounded whole-bag count.
Pour Guidance turns volume, waste, depth, bag count, and ticket size into review statuses such as Typical range, Crew planning, Short-load likely, or Truck planning.
Bag Count Comparison shows the whole-bag count for each mix size so a large selected-bag number is harder to miss.
JSON is useful when the exact inputs and outputs need to move into a quote note or job record.

For many simple pours, a waste setting between 5% and 15% is a practical first pass. Use less only when measurements and forms are tight enough to justify it. Use more for rough excavation, thickened edges, irregular forms, extra cleanup room, or supplier minimums. The Waste allowance status will flag values below 5% as Low buffer and values above 15% as High buffer.

Do not treat the cheapest material row as the full job cost. The optional bag and ready-mix prices cover material only. Delivery, short-load fees, pump charges, tools, reinforcement, tax, base prep, curing supplies, and labor are outside those numbers.

Before ordering, compare Final concrete volume, Ready-mix ticket, Selected bag order, and the Assumptions row. If those agree with the measured shape, product label, supplier quote, and site access, the estimate is ready for a concrete conversation with the supplier or installer.

Step-by-Step Guide:

Use this sequence when you want a concrete quantity that can be checked against bag labels and ready-mix quotes.

Set Measurement system. Confirm that length, depth, volume, and density units changed to the system you intend to use.
Choose Pour type. For a slab or footing, fill Slab length or Footing length, the matching width field, and Slab thickness or Footing depth. For a round pier, fill Hole or pier diameter and Pier or hole depth. For a known takeoff, enter Concrete volume.
Enter Identical pours as a whole count. If the input is blank or fractional, the calculator snaps it to at least 1 matching pour.
Set Waste allowance. Watch Pour Guidance for Low buffer, Typical range, or High buffer before trusting the final quantity.
Choose Ready-mix rounding. Use Exact volume for pure math, or round up to 0.25 yd3, 0.5 yd3, or whole yd3 when matching a supplier ticket increment.
Pick Selected bag size. Check Bag Order and Bag Count Comparison to see whether the selected bag count is practical for the crew and mixing setup.
Open Advanced only when prices or weight matter. Fill Selected bag price and Ready-mix price for material-only cost comparison, or enter Concrete density to show Estimated concrete weight.
If the red Check concrete inputs alert appears, fix the named field. Result rows stay empty until every required dimension or known volume is greater than zero.
Review Concrete Takeoff, Bag Order, and Pour Guidance before copying or downloading tables, chart data, or JSON.

Interpreting Results:

The order conversation usually starts with Final concrete volume and Ready-mix ticket. Final concrete volume is the calculated amount after waste. Ready-mix ticket is the cubic-yard quantity after the chosen upward rounding rule.

Base concrete volume is the measured shape before extra allowance.
Waste allowance volume is the added buffer created by the waste percent.
Selected bag order is rounded to whole bags for the chosen bag size.
Bag labor moves to Crew planning above 40 selected bags and High count above 80 selected bags.
Ready-mix quote shows Short-load likely below 1 yd3 and Truck planning above 10 yd3.

A green or positive-looking status does not mean the pour is structurally correct. Common band for slab thickness only means the entered thickness sits in a familiar light-to-medium planning range. Footing depth, reinforcement, soil, frost depth, load, and code requirements still need the project drawing or a qualified reviewer.

The best verification cue is agreement across the result rows. Check that Total footprint area, Base concrete volume, Waste allowance volume, Ready-mix ticket, and Selected bag order all describe the same real job. If one row looks surprising, recheck units, repeated pours, depth, and bag yield before using the quantity.

Worked Examples:

Small slab with ready-mix rounding

A 12 ft by 10 ft slab at 4 in thick with 1 identical pour and 10% waste produces a Base concrete volume of about 1.48 yd3 and a Final concrete volume of about 1.63 yd3. With Ready-mix rounding set to 0.25 yd3, Ready-mix ticket becomes 1.75 yd3. The default 80 lb row shows 74 bags, which explains why the Order lane is Crossover rather than an automatic bag job.

Deck piers with a moderate bag count

Six round holes at 12 in diameter and 36 in filled depth total about 15.6 cu ft after 10% waste, or roughly 0.58 yd3. If the selected bag is 60 lb, Selected bag order is 35 bags because each 60 lb bag is modeled at 0.45 cu ft. Order lane lands on Small pour, so bag labor, mixer access, and short-load pricing should all be compared.

Known metric volume from a separate takeoff

A drawing takeoff that already gives 0.45 m3 for one section can use Known volume. With 2 identical pours and 5% waste, Final concrete volume is 0.945 m3 / 1.24 yd3. Quarter-yard rounding raises Ready-mix ticket to 1.25 yd3, and Volume source in Pour Guidance reminds you that the entered known volume was trusted before allowance was added.

Troubleshooting a missing result table

If a slab estimate shows Check concrete inputs and the first message says Slab width must be greater than zero, the result tables remain empty. Enter a positive Slab width, then reopen Concrete Takeoff. The table should now show Total footprint area, Base concrete volume, and the downstream ordering rows.

FAQ:

Why does the ready-mix ticket exceed the final volume?

The Ready-mix ticket rounds Final concrete volume upward when quarter-yard, half-yard, or whole-yard rounding is selected. The Ready-mix ticket row reports the extra rounded volume so you can see the difference.

Why are bag counts always whole numbers?

Bag Order divides final cubic feet by each bag yield, then rounds up. A calculated need of 73.3 bags becomes 74 bags because a partial bag cannot cover the remaining concrete volume by itself.

Can I use the cost comparison as an installed price?

No. Ready-mix material cost and selected-bag cost use only the optional material prices you enter. Delivery, short-load, pump, tax, reinforcement, equipment, base prep, curing, and labor are not included.

What does the density field change?

Concrete density only controls the optional Estimated concrete weight row. Leave it at 0 when weight is not needed, or enter a supplier or mix-design value when a rough load check matters.

Why did the calculator ask me to check inputs?

The red alert appears when a required dimension or known volume is missing, zero, or invalid. Fix the named field, such as Hole or pier diameter or Known concrete volume, and the result rows will return.

Glossary:

Base concrete volume: The measured shape volume before waste allowance is added.
Final concrete volume: The base volume plus the selected waste allowance.
Ready-mix ticket: The cubic-yard quantity after the selected upward rounding increment is applied.
Waste allowance: The extra percentage added for field variation, spillage, irregular forms, and ordering margin.
Bag yield: The approximate mixed volume one bag supplies, measured here in cubic feet.
Order lane: The volume-based guidance label that compares bag-friendly, small-pour, crossover, and ready-mix likely ranges.

References:

CIP 31 - Ordering Ready Mixed Concrete, National Ready Mixed Concrete Association.
Concrete Mix Product No. 1101 Data Sheet, QUIKRETE.
Appendix C - Proposed Revisions to the AASHTO Standard Specifications for Highway Bridges, Federal Highway Administration, October 2006.