Ordering ready-mix concrete or buying enough pre-mixed bags for a slab, footing, or patio project requires converting the slab's dimensions into a volume — a calculation that trips people up because thickness is usually measured in inches while length and width are in feet.
This calculator handles the unit conversion automatically: enter your slab's length and width in feet and thickness in inches, and it calculates the total volume in both cubic feet and cubic yards (the unit ready-mix concrete is typically ordered in), plus how many standard bags that translates to if you're buying bagged concrete.
For anything beyond a small DIY slab, ordering ready-mix delivered by the cubic yard is usually more practical and cost-effective than buying dozens of individual bags.
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Frequently asked questions
Why is thickness measured in inches while length and width are in feet?
This just reflects common practice — slabs are typically only a few inches thick, so inches give a more precise, practical measurement than a small fraction of a foot.
Should I order extra concrete beyond the calculated amount?
Yes, ordering roughly 5-10% extra is common practice to account for spillage, uneven subgrade, and measurement variance, especially for ready-mix deliveries where running short mid-pour is a serious problem.