Calculate exact concrete volume for slabs, footings, and columns. Instantly find out how many cubic yards or pre-mixed bags (60lb/80lb) you need to buy.
Concrete Calculator
Instantly estimate exact yards and premixed bag limits required for slabs, footings, and stairs.
Plot Dimensions
Total Volume
Premixed Bag Estimates
*Built-in algorithm assuming standard yield rates. Buy ~10% extra for spillage contingency.
How to Calculate Concrete Volume mathematically
Whether you are pouring a small DIY patio or setting sonotubes for a deck, buying the wrong amount of concrete is an expensive mistake. Concrete is universally measured and sold in exactly two ways: Cubic Yards (for large automated truck deliveries) and Pre-mixed Bags (for manual mixing).
To manually calculate the cubic yards required for a standard rectangular slab of concrete, use this formula:
Length (ft) × Width (ft) × Depth (ft) = Total Cubic Feet Total Cubic Feet ÷ 27 = Total Cubic Yards Note on Depth: Most concrete slabs are poured 4 inches thick. You must divide 4 by 12 (0.33) to convert inches into feet before running the primary multiplication block. Our calculator handles this conversion dynamically for you.
The Premixed Bag Estimator Guide
If your project is smaller than a cubic yard, you will be buying bags of pre-mixed concrete from a hardware store. Standard yields per bag are incredibly rigid:
- 40lb = 0.011 cubic yards
- 60lb = 0.017 cubic yards
- 80lb = 0.022 cubic yards
When to Order a Ready-Mix Truck instead?
The golden rule of DIY concrete is the "1.5 Yard Threshold".
Mixing one cubic yard of concrete by hand requires wrestling with entirely too many 80lb bags (about 45 bags). If your calculator output shows anything over 1.5 cubic yards, standard industry practice is to call a local ready-mix plant and have a physical cement truck deliver the batch wet.
Frequently Asked Questions
How much concrete do I need for a 10x10 foot slab at 4 inches thick?
A 10x10 slab poured at the standard residential depth of 4 inches requires exactly 1.23 cubic yards of concrete. This translates to roughly 56 x 80-lb bags of pre-mix.
Should I factor in spillage or waste?
Yes. Absolute mathematical volume rarely translates perfectly to real life. The ground may be slightly uneven, forms might bow, or spills can occur. Always add a 10% waste contingency margin to your final bag count or yardage order to avoid being short during the cure window.
The tools and calculators provided on The Simple Toolbox are intended for educational and informational purposes only. They do not constitute financial, legal, tax, or professional advice. While we strive to keep calculations accurate, numbers are based on user inputs and standard assumptions that may not apply to your specific situation. Always consult with a certified professional (such as a CPA, financial advisor, or attorney) before making significant financial or business decisions.
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