Concrete

Concrete Calculator

Enter the project shape, surface dimensions, slab depth, and waste factor to estimate concrete volume and bag counts.

Planning estimate

This calculator provides a planning estimate only. Material coverage, compaction, waste, surface conditions, product yield, and installation methods can change the final quantity needed. Always check the product label and local supplier guidance before purchasing materials.

How To Use This Calculator

Step 1 Choose the shape that matches the pour. Use rectangle for slabs, patios, walkways, shed pads, and driveway panels. Use circle for round pads, and custom area when you already know the square footage.
Step 2 Enter slab depth in inches. Four inches is common for many small slabs, while six inches or more may be used for heavier loads or local requirements.
Step 3 Keep the waste factor visible while planning. The calculator shows the clean volume and the adjusted volume so you can compare exact math with a practical shopping quantity.

What The Result Means

The concrete result separates volume from bag count because those are different buying decisions. Cubic yards help when ordering ready-mix or comparing delivery quotes. Bag counts help for small projects where you are buying dry mix. The 40 lb, 60 lb, and 80 lb estimates use generic yields and should be checked against the product label.

If you are still measuring the surface, use the square footage calculator first, then bring the area back to this concrete calculator.

Before You Buy

Confirm whether the project needs permits, reinforcement, expansion joints, or a specific slab thickness.
Check the concrete bag yield printed on the exact product you plan to buy.
Measure the formed area after stakes and boards are set, not only from the first sketch.
Plan water, mixing, wheelbarrow access, and cleanup before opening bags.

Accuracy Notes

Uneven subgrade can add volume beyond the rectangular calculation.
Small pours can lose material to mixing tubs, tools, and spillage.
Ready-mix orders are usually rounded by supplier policy, not by this calculator alone.

Formula

Cubic feet = area_sqft × depth_inches / 12

Cubic yards = cubic_feet / 27

Adjusted volume = volume × (1 + waste_factor)

Bags = adjusted_cubic_feet / bag_yield

Example Project

A 10 ft by 10 ft patio at 4 in thick is 33.33 cubic feet, or 1.23 cubic yards, before waste.

Waste Factor

Use 5-10% for simple forms and clean bases. Increase the allowance for uneven subgrade, hand mixing, long edges, or small pours where spill loss matters.

Unit Notes

Depth is entered in inches because slab thickness is commonly specified as 4 in or 6 in. Results include cubic feet, cubic yards, and cubic meters.

Common Mistakes

Using inches as feet for slab depth.
Ordering exact volume with no allowance for uneven base.
Assuming every bag size has the same yield.

FAQ

How many 80 lb bags are in one cubic yard?

Using a generic 0.60 cubic foot yield, one cubic yard takes about 45 bags. Product labels can differ, so confirm the yield before buying.

Should I use cubic yards or bag counts?

Use cubic yards when ordering ready-mix or bulk material. Use bag counts for small slabs, post pads, walkways, and repair work.

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