Concrete Calculator
Calculate cubic yards, cubic feet, and 60lb/80lb premixed bags.
A concrete calculator - or concrete slab estimator, concrete measurement calculator, or concrete pad calculator - estimates how much concrete you'll need for a slab, footing, column, or other pour, in cubic yards, cubic feet, and the number of premixed bags required. Getting this estimate right matters because concrete is typically sold and priced in fixed increments - ordering too little can halt a pour partway through, while overordering wastes money on unused material.
Enter the length, width, and depth of your project (or the dimensions for a footing, column, or circular slab) to answer how much concrete do i need for the pour.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 10ft x 10ft slab at 4 inches thick | 1.23 Cubic Yards (56 bags @ 80lb) | 33.3 cubic feet requires ~1.23 yards of concrete. |
Popular Scenarios & Specific Calculations
Why Concrete Is Measured in Cubic Yards
Ready-mix concrete is typically ordered by the cubic yard from suppliers, since that's the standard unit for truck-delivered concrete in the U.S. This calculator converts your project's length, width, and depth (all typically measured in feet and inches) into cubic yards by dividing the total cubic footage by 27, the number of cubic feet in a cubic yard.
Bagged Concrete vs. Ready-Mix Delivery
For small projects, premixed bags (commonly sold in 60 lb and 80 lb sizes) are more practical than ordering a truck delivery, which usually has a minimum order size. An 80 lb bag yields approximately 0.6 cubic feet of mixed concrete, meaning it takes roughly 45 bags to equal one cubic yard - for larger pours, ready-mix delivery becomes more cost-effective despite the delivery minimum.
Always Order a Buffer Above the Calculated Amount
Because ground isn't perfectly level, forms can shift slightly, and some material is inevitably lost to spillage or absorption into the sub-base, most contractors add a 5-10% buffer above the calculated volume when ordering concrete. Running short partway through a pour is a much bigger problem than having a small amount left over, since concrete begins hardening quickly once mixed.
How to Use the Concrete Calculator
- Open the Concrete Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the concrete calculator works.
Frequently Asked Questions
How many 80lb bags of concrete make a cubic yard?
It takes approximately 45 bags of 80lb premixed concrete to equal one cubic yard.
How much concrete do I need for a 10x10 slab?
For a 10ft x 10ft slab at a standard 4-inch thickness, you'd need about 1.23 cubic yards of concrete (100 sq ft x 0.33 ft depth = 33.3 cubic feet, divided by 27).
Should I order extra concrete beyond the calculated amount?
Yes, most contractors add a 5-10% buffer to account for uneven ground, form shifting, and material loss - running short mid-pour is a bigger problem than having some left over.
What's the difference between 60lb and 80lb bags of concrete?
They contain the same concrete mix at different bag sizes - an 80lb bag yields more mixed concrete per bag (roughly 0.6 cubic feet) than a 60lb bag, so fewer 80lb bags are needed for the same job.
How thick should a concrete slab be?
A standard residential slab (like a patio or walkway) is commonly 4 inches thick, while slabs supporting heavier loads (like a driveway or garage floor) are often 5-6 inches or more - check local building codes for specific requirements.
When should I order ready-mix instead of bagged concrete?
For larger pours (typically more than 1-2 cubic yards), ready-mix delivery is usually more cost-effective and less labor-intensive than mixing dozens of bags by hand, despite most suppliers having a minimum order quantity.
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Last updated: September 29, 2026.