Concrete calculator FAQ
A few things to check before you turn an estimate into an order.
How many 60 lb or 80 lb bags make a cubic yard?
With the nominal yields used here, one cubic yard needs 60 of the 60 lb bags (27 ÷ 0.45), or 45 of the 80 lb bags (27 ÷ 0.60), before waste. These are alternatives. Check the yield for your specific product.
Why do the bag yields matter?
Bag weight is not finished volume. This calculator uses approximately 0.45 ft³ per 60 lb bag and 0.60 ft³ per 80 lb bag, as published for QUIKRETE Concrete Mix No. 1101. Lightweight, specialty, and other mixes may have different yields. Do not apply these numbers to every product.
How much waste should I add?
The calculator starts at 10%, but you can choose 0–50%. That starting point is an allowance, not a manufacturer recommendation or a guarantee. Uneven ground, spills, and measurement uncertainty can change what you need. Check with your supplier for your project.
What is the difference between a slab and a footing here?
Both use length × width × depth. The slab labels its vertical measurement thickness; the footing labels it depth. The calculator does not decide which size is safe or suitable for a foundation.
Does the column estimate subtract a post or hollow center?
No. It estimates a solid cylinder from its full diameter and height. A hole with a post or a hollow tube needs a different volume calculation.
Can I enter metric dimensions?
Yes. Enter lengths in meters and thickness, depth, or column diameter in millimeters, as labeled. Switching units converts complete measurements exactly. An unfinished or invalid entry stays with the unit where you typed it, and each shape keeps its own entries.
Why did my result disappear after I changed a field?
Results are cleared whenever an input changes so you do not order from an old estimate. Select Calculate concrete again.
Why round up when the displayed volume looks like a whole number of bags?
The displayed volume has only two decimal places. Bag counts use the full value, including any amount above a whole-bag boundary. A small positive project can show less than 0.01 cubic feet and still require one bag.
Is zero an error?
A valid zero dimension produces zero volume and zero bags. A missing or invalid measurement does not produce an estimate. Check your dimensions if a zero result was unexpected.
Is this structural engineering advice?
No. These are material estimates only. Follow local requirements and consult a qualified professional about structural design, reinforcement, strength, and safe dimensions.