CalcReady Mix Concrete Calculator
Last updated: 2026-08-24
TL;DR: To calculate ready-mix concrete volume in cubic yards, multiply the slab’s length (feet) by its width (feet) by its depth (inches converted to feet by dividing by 12), then divide the total cubic feet by 27, using the formula: cubic yards = (length in ft × width in ft × (depth in in ÷ 12)) / 27.
What Is the Ready Mix Concrete Calculator?
The Ready Mix Concrete Calculator estimates the exact volume of concrete you need for a slab, footing, or column project before you order from a concrete supplier. Instead of guessing and risking costly over-ordering or a short pour, this tool converts your project’s three dimensions—length, width, and depth—directly into cubic yards, the standard unit used by ready-mix concrete trucks.
Whether you are pouring a patio slab, a rectangular foundation footing, or a vertical column, this calculator saves time and money. Ready-mix concrete is typically ordered by the cubic yard, with a minimum delivery often around 1 to 3 cubic yards. A single cubic yard covers 81 square feet at 4 inches deep. Misjudging the volume by even half a yard can result in a $50–$100 surcharge for a short load or the headache of disposing of leftover concrete. This tool eliminates that guesswork.
How to Use the Calculator
Follow these three simple steps to get your concrete volume in cubic yards. The calculator accepts measurements in feet for length and width, and inches for depth (or height, for columns).
- Choose the shape of your pour. Select from Slab (flat, rectangular surface), Footing (horizontal support base), or Column (vertical cylindrical or rectangular pillar). The shape determines whether the calculator treats depth as thickness (slab/footing) or height (column).
- Enter the dimensions. Input the length (ft), width (ft), and depth (in) into the corresponding fields. For a column, depth equals the height of the column in inches. All measurements must be in their correct units—feet for length and width, inches for depth.
- Click calculate. The calculator instantly returns the result in cubic yards, rounded to two decimal places (e.g., 3.47 cubic yards). Use this number to order your ready-mix concrete.
Formula and Calculation Method
The calculator performs a straightforward three-step conversion. First, it converts the depth from inches to feet because length and width are already in feet. Then it calculates the total cubic feet of the pour. Finally, it converts cubic feet into cubic yards, since concrete is purchased by the cubic yard.
The formula in plain language:
- Convert depth from inches to feet: depth (ft) = depth (in) ÷ 12
- Find the volume in cubic feet: cubic feet = length (ft) × width (ft) × depth (ft)
- Convert to cubic yards: cubic yards = cubic feet ÷ 27
Mathematically:
cubic yards = (length × width × (depth ÷ 12)) ÷ 27
Worked example with real numbers:
Suppose you are pouring a concrete patio slab that is 12 feet long, 10 feet wide, and 6 inches deep.
- Step 1: Depth in feet = 6 ÷ 12 = 0.5 ft
- Step 2: Cubic feet = 12 × 10 × 0.5 = 60 cubic feet
- Step 3: Cubic yards = 60 ÷ 27 = 2.22 cubic yards
You would order 2.25 cubic yards (2.22 rounded up slightly) to ensure you have enough concrete for the slab, accounting for small variations in the ground or formwork.
Practical Examples
| Project Type | Length (ft) | Width (ft) | Depth (in) | Calculated Cubic Yards | What It Means |
|---|---|---|---|---|---|
| Small concrete pad (garbage can or AC unit) | 4 | 4 | 4 | 0.20 | Less than 1 yard—order from a batch plant with a short-load fee, or mix bagged concrete. |
| Standard walkway | 20 | 3 | 4 | 0.74 | Just under 1 cubic yard. Most suppliers require a 1-yard minimum, so you’d order 1 yard and use the excess for stepping stones or a small pad. |
| Large garage foundation | 24 | 20 | 5 | 7.41 | Order 7.5 cubic yards. A standard concrete truck holds about 10 yards, so one truckload will cover this pour. |
| Square column (height as depth) | 0.5 (6 in width) | 0.5 (6 in width) | 72 (height) | 0.17 | Very small volume—mix by hand or use a 60-lb bag calculator. Ready-mix minimums make this impractical for truck delivery. |
Tips for Accurate Results
Always convert units before calculating. The most common mistake is forgetting that depth is entered in inches while length and width are in feet. If you accidentally enter depth as 6 (feet) instead of 6 (inches), your result will be 12 times too large—meaning you’d order 26.67 cubic yards when you only need 2.22 yards. The calculator handles the inches-to-feet conversion internally, but do not pre-convert depth to feet yourself.
Measure from the actual forms, not from plan drawings. When pouring a slab, measure the inside dimensions of your wood forms or the excavated hole. Forms can bow inward or outward by an inch or two, changing the actual volume. Always take three measurements along the length and width and use the average for the most accurate result.
Account for over-excavation or sloppy forms. If your trench for a footing is wider than planned, or the ground is uneven, add 5% to 10% to the calculated volume. The formula assumes perfectly straight, uniform dimensions—real-world conditions rarely are. Adding a small waste factor (0.5 to 1.0 cubic yards for large pours) prevents a short pour.
For columns, remember that ‘depth’ means height. The calculator uses the same input field name ‘depth’ for all shapes. For a column, enter the column’s height in inches, not its diameter or cross-section. The length and width fields represent the column’s cross-sectional dimensions (e.g., 1 foot by 1 foot for a 12-inch square column).
Frequently Asked Questions
How do I convert my calculated cubic yards into bags of concrete mix?
Ready-mix concrete comes by the truck, but smaller projects often use bagged concrete. Each 60-pound bag yields about 0.45 cubic feet of concrete, and each 80-pound bag yields about 0.60 cubic feet. Since there are 27 cubic feet in a cubic yard, divide your cubic yard result by the bag yield. For example, a 0.50 cubic yard slab (13.5 cubic feet) requires 30 bags of 60-pound mix (13.5 ÷ 0.45 = 30) or 23 bags of 80-pound mix (13.5 ÷ 0.60 = 22.5, round up to 23). Note that bagged concrete has lower compressive strength than ready-mix and is only practical for volumes under 1 cubic yard.
Why is concrete measured in cubic yards and not cubic feet?
Ready-mix concrete trucks carry concrete in revolving drums with capacities measured in cubic yards (a standard truck holds 8 to 10 cubic yards). Because a cubic yard is 27 times larger than a cubic foot, using cubic yards keeps the numbers manageable for ordering. A 30-foot by 20-foot slab at 4 inches deep equals 7.4 cubic yards—ordering “7.4 cubic yards” is much clearer than “200 cubic feet.” The construction industry adopted cubic yards decades ago for consistency across batch plants, delivery trucks, and job site forms.
What happens if I order too little or too much ready-mix concrete?
Ordering too little concrete is the bigger problem. If the truck runs out before your pour is complete, you cannot simply add more after a delay—it creates a cold joint, a weak seam where old concrete meets new. You would need to tear out and repour, or live with a structurally compromised slab. Most contractors order 5% to 10% extra (e.g., 2.2 cubic yards calculated → order 2.5 cubic yards). Ordering too much means paying for unused concrete that hardens in the truck—the driver must dispose of it, and you will be billed for the overage. This is less damaging than a short pour but still costs money. Use the calculator precisely and then add a small waste factor to balance the risk.
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FAQ
What is a Ready Mix Concrete Calculator used for?
This calculator estimates the volume of ready mix concrete needed for a project based on dimensions like length, width, and depth. It helps you avoid over-ordering or under-ordering material, saving both time and money on construction or DIY projects.
Does the calculator account for waste or spillage?
Yes, most Ready Mix Concrete Calculators include an optional waste factor, typically 5-10%, to cover spillage, uneven subgrades, or slight over-excavation. This ensures you have enough concrete to complete the job without running short.
What units of measurement can I use with this calculator?
The calculator supports both imperial units (such as feet and inches) and metric units (such as meters and centimeters) for inputting dimensions. It then provides the concrete volume in cubic yards or cubic meters, depending on your selected system.
Can I use this calculator for irregularly shaped areas like circles or columns?
Yes, many Ready Mix Concrete Calculators offer options for different shapes, including slabs, columns, footings, and circular patios. You simply input the specific dimensions for the shape, and the calculator will compute the precise volume needed.