Concrete Calculator: Calculate Your Concrete Needs
Enter your project dimensions to calculate concrete volume, cubic yards, bag quantities, and optional material cost.
What This Tool Does
Enter the dimensions or known concrete volume for your project, choose the applicable calculation type, and the calculator determines the required concrete quantity in cubic feet and cubic yards, along with bag quantities and optional material cost where applicable.
Concrete Calculator
Calculate concrete volume, cubic yards, bag quantities, and optional material cost for your project.
How This Concrete Calculator Works
Choose your project type and enter the required dimensions or a known concrete volume. The calculator converts the result into cubic feet and cubic yards, estimates bag quantities for common bag sizes, and can calculate an optional material cost from the price you enter.
Enter Your Project Details
What If?
Try a different valid input and recalculate automatically to see how the concrete requirement changes.
Recent Calculations
Your recent calculations for this page session will appear here.
Compare Scenarios
Save up to three calculated scenarios to compare their concrete quantities side by side.
Understanding Your Result
The calculator first determines the concrete volume from your project dimensions or known volume. It then applies the selected waste allowance and converts the adjusted quantity into cubic feet, cubic yards, cubic meters, and approximate bag quantities.
- Rectangular volume = length × width × thickness.
- Round volume = π × radius² × height.
- 1 cubic yard = 27 cubic feet.
- Bag quantities use approximate reference yields and should be checked against the actual product yield before purchase.
Usage Tips
- Use consistent units and dimensions throughout a calculation.
- Adjust the waste allowance when you need additional material beyond the geometric volume.
- Bag yields vary by product, so verify the yield printed on the specific concrete mix you plan to use.
- For ready-mix orders, confirm the final quantity and supplier requirements before ordering.
Concrete Calculator
A concrete calculator helps estimate how much concrete a project requires from its dimensions or a known volume. This page explains how the calculation works, how cubic feet and cubic yards relate to one another, how bag quantities are estimated, and how the optional material-cost calculation is produced.
Quick Answer
To calculate the concrete needed for a rectangular project, multiply length by width by thickness after converting all dimensions to the same unit. The resulting cubic feet can then be divided by 27 to get cubic yards. This calculator adds the selected waste allowance and also shows approximate quantities for 40 lb, 50 lb, 60 lb, and 80 lb concrete bags.
Core formulas: Rectangular volume = length × width × thickness. Cubic yards = cubic feet ÷ 27. The calculator then applies the selected waste percentage before displaying the quantity to plan for.
What This Concrete Calculator Helps You Calculate
The calculator is designed for common concrete quantity-estimation tasks rather than structural engineering or concrete mix design. You can calculate a slab or pad, a footing or trench, a round column or post hole, or start with a known concrete volume.
| Calculation Type | Main Inputs | Primary Result |
|---|---|---|
| Slab / Pad | Length, width, thickness, number of pours | Concrete volume |
| Footing / Trench | Length, width, depth, number of pours | Concrete volume |
| Round Column / Post Hole | Diameter, height or depth, number of pours | Concrete volume |
| Known Volume | Volume and unit | Converted concrete quantity |
The results are presented as cubic feet, cubic yards, and cubic meters after the selected waste allowance is applied. The calculator also estimates how many bags would be needed using its reference yields.
How to Calculate Concrete Volume
Rectangular Slabs and Pads
A rectangular concrete slab uses three dimensions: length, width, and thickness. If length and width are measured in feet and thickness is measured in inches, the thickness is converted to feet before multiplying.
For example, a 10 ft × 10 ft slab that is 4 inches thick has a geometric volume of approximately 33.33 cubic feet. Dividing 33.33 by 27 gives approximately 1.23 cubic yards before any waste allowance is added.
Footings and Trenches
A footing or trench uses the same rectangular-volume concept. The length is combined with the width and depth to determine the volume. The calculator also allows you to enter the number of identical pours so repeated sections can be included in one calculation.
Round Columns and Post Holes
A round concrete section uses the area of a circle multiplied by its height or depth. The calculation uses the radius, which is half of the diameter, and then multiplies the result by the number of identical pours.
Known Concrete Volume
When the required volume is already known, the calculator can accept cubic feet, cubic yards, or cubic meters and convert that value into the other supported volume units.
Concrete Calculator: Cubic Yards and Cubic Feet
Concrete suppliers commonly use cubic yards when discussing ready-mix quantities, while project measurements are often calculated in feet and inches. One cubic yard equals 27 cubic feet, so converting between the two is a normal part of concrete estimating.
| Volume | Equivalent |
|---|---|
| 1 cubic yard | 27 cubic feet |
| 2 cubic yards | 54 cubic feet |
| 3 cubic yards | 81 cubic feet |
| 5 cubic yards | 135 cubic feet |
For this reason, a concrete yard calculator and a concrete volume calculator are closely related concepts. The important distinction is that this page combines the volume calculation with concrete-specific bag and cost estimates.
How Many Bags of Concrete Do You Need?
Bag quantity depends on the volume required and the yield of the particular concrete product. Bag size alone does not determine the exact amount of concrete produced. Manufacturers publish approximate yields for their products, and those values should be checked before purchasing.
For the reference yields used by this calculator, QUIKRETE Concrete Mix lists approximately 0.30 cubic feet for a 40 lb bag, 0.375 cubic feet for a 50 lb bag, 0.45 cubic feet for a 60 lb bag, and 0.60 cubic feet for an 80 lb bag.
| Bag Size | Reference Yield | Approximate Bags per Cubic Yard |
|---|---|---|
| 40 lb | 0.30 ft³ | 90 |
| 50 lb | 0.375 ft³ | 72 |
| 60 lb | 0.45 ft³ | 60 |
| 80 lb | 0.60 ft³ | 45 |
These are yield-based reference values, not universal bag counts for every concrete product. The actual product label or manufacturer data should be checked before ordering. QUIKRETE also states that its quantity calculations use approximate yields and that its calculator rounds bag quantities upward.
See the QUIKRETE Concrete Mix technical data for the published yields used as the reference basis here.
Why Add a Waste Allowance?
A geometric calculation gives the theoretical volume based on the dimensions entered. Real projects can require additional material because measured dimensions and actual placement conditions are not perfectly represented by a simple volume calculation.
The calculator therefore lets you adjust the waste allowance rather than treating one percentage as universally correct. Sakrete's estimating guidance recommends adding 10% to concrete estimates, while QUIKRETE notes that its approximate yields do not account for uneven substrate or waste.
For this reason, the waste percentage should be understood as an estimating adjustment. It is not a structural requirement and should not be interpreted as a guaranteed amount of additional concrete needed for every project.
The Sakrete guide to estimating bagged concrete jobs provides additional discussion of volume calculations and estimating allowances.
How the Concrete Cost Calculator Works
The optional cost calculation uses the price you enter rather than assuming a fixed market price. You can select ready-mix pricing per cubic yard or bagged-concrete pricing per bag.
| Cost Type | Calculation |
|---|---|
| Ready-mix | Adjusted cubic yards × price per cubic yard |
| Bagged concrete | Required bags for the selected size × price per bag |
These calculations estimate material cost only. They do not include delivery, pumping, labor, reinforcement, finishing, site preparation, taxes, permits, or other project expenses.
Practical Examples
Example 1 — 10 × 10 ft Slab at 4 Inches
User situation: A user needs a quantity estimate for a square slab.
Example inputs: 10 ft length × 10 ft width × 4 in thickness, one pour, 10% waste.
Result: About 36.67 cubic feet, or 1.36 cubic yards, after the 10% allowance.
Interpretation: Using the reference yields in the calculator, the estimated bag quantities are about 123 of the 40 lb bags, 98 of the 50 lb bags, 82 of the 60 lb bags, or 62 of the 80 lb bags.
Example 2 — 10 × 20 ft Slab at 4 Inches
User situation: A rectangular slab has twice the floor area of the first example but the same thickness.
Example inputs: 20 ft length × 10 ft width × 4 in thickness, one pour, 10% waste.
Result: About 73.33 cubic feet, or 2.72 cubic yards, after the allowance.
Interpretation: Doubling one horizontal dimension doubles the calculated volume when the other inputs remain unchanged.
Example 3 — 20 ft Footing, 8 × 8 Inches
User situation: A user is estimating concrete for a continuous rectangular footing.
Example inputs: 20 ft length × 8 in width × 8 in depth, one pour, 10% waste.
Result: About 9.78 cubic feet, or 0.36 cubic yards, after the allowance.
Interpretation: The same volume method applies to the footing, but the dimensions are expressed according to the shape of the project.
How to Get More Useful Results
Measure the project as accurately as practical and keep track of whether each dimension is expressed in feet or inches. For slabs, thickness can have a large effect on the final quantity because it is multiplied across the entire length and width.
When ordering bagged concrete, verify the yield printed on the exact product you plan to use. Different concrete mixes can have different yields even when their bag weights are similar.
When ordering ready-mix concrete, use the calculated cubic-yard result as an estimate and confirm the final quantity with your concrete supplier. The supplier can account for its ordering practices and the specific requirements of the project.
Concrete Calculator vs. Concrete Mix Calculator
The terms are sometimes used interchangeably, but they can describe different tasks. A concrete quantity calculator determines how much material is required for a specified volume. A concrete mix-design calculation can involve selecting proportions and properties for a particular concrete specification.
This SooperTools calculator is a quantity estimator. Its bag calculation tells you approximately how many bags of a selected size correspond to the calculated volume. It does not design a structural concrete mix or determine a required compressive strength.
Common Questions
How do I calculate how much concrete I need?
Calculate the project's volume from its dimensions, convert the result into cubic yards when needed, and then account for the selected waste allowance. For a rectangular area, multiply length by width by thickness after converting the measurements to compatible units.
How do I calculate cubic yards of concrete?
First calculate cubic feet. Then divide the cubic-foot result by 27 because one cubic yard contains 27 cubic feet.
How many bags of concrete do I need?
Divide the required volume by the approximate yield of the specific bagged concrete product. The number changes with both total volume and bag size.
How many 80 lb bags of concrete do I need?
The answer depends on the volume and the product yield. The calculator uses an approximate reference yield of 0.60 cubic feet per 80 lb bag for its bag estimate, so the actual product should still be checked before purchase.
How much concrete do I need for a slab?
Enter the slab length, width, thickness, number of identical pours, and waste allowance. The calculator then converts the resulting volume into cubic yards and bag quantities.
How is the concrete cost calculated?
Ready-mix cost is calculated from adjusted cubic yards multiplied by the price per cubic yard you enter. Bagged-concrete cost uses the calculated number of bags for the selected size multiplied by the price per bag.
Frequently Asked Questions
Yes. The calculator includes separate Slab / Pad and Footing / Trench modes, as well as a Round Column / Post Hole mode and a Known Volume mode.
The waste allowance increases the calculated quantity by the percentage you enter. It is an estimating adjustment and should not be treated as a universal project requirement.
Common bag sizes produce different volumes of concrete. Showing several sizes lets you compare the approximate number of bags required for the same project volume.
No. Bag quantities are estimates based on reference yields. The actual yield should be confirmed from the specific product's manufacturer information or packaging.
Yes. You can enter a ready-mix price per cubic yard or a bag price for the selected bag size. The calculator then provides an estimated material cost.
No. This tool estimates concrete quantity, cubic yards, bag quantities, and optional material cost. It does not design a structural concrete mix or select a required concrete strength.
Treat the result as an estimate. Before purchasing, confirm the specific bag yield or ready-mix supplier requirements and account for actual project conditions.
Yes. The Known Volume mode accepts cubic feet, cubic yards, or cubic meters and converts the value into the other supported units before calculating the remaining outputs.
Related SooperTools Calculators
For a general calculation involving cubic yards rather than concrete-specific bag and material planning, see the Cubic Yard Calculator.
For another construction-related planning task, see the Board and Batten Calculator.
For roof-framing calculations, the Rafter Calculator handles a separate construction measurement problem.
Limitations
- The calculator provides material estimates, not structural engineering calculations.
- Bag quantities depend on the reference yields used by the calculator and may differ for other products.
- Waste allowance is an estimating adjustment and may not reflect every project condition.
- Material cost depends on the prices entered by the user and does not represent a fixed market price.
- Cost results do not include labor, delivery, pumping, reinforcement, preparation, permits, taxes, or other project expenses.
- For structural or code-sensitive projects, project dimensions and construction requirements should be confirmed from the applicable plans, specifications, and qualified professionals.
References
- QUIKRETE Concrete Calculator for concrete quantity estimation and approximate bag calculations.
- QUIKRETE Concrete Mix Technical Data for published bag sizes and approximate product yields.
- Sakrete: Estimating Bagged Concrete Jobs for concrete volume, cubic-yard conversion, and estimating guidance.
Written by: SooperTools Editorial Team
Last updated: October 2, 2026
Important: Concrete quantities are estimates based on the information entered and the reference yields used by the calculator. Check the exact product specifications and project requirements before ordering or placing concrete.