Materials calculator · concrete slab v1.1
Concrete Slab Calculator
Calculate the geometric slab requirement first, then see contingency, practical ready-mix order, bag equivalent, approximate weight and procurement cost separately.
✓No signup
✓Formula shown
✓Editable assumptions
✓US planning estimate
Step 1
Slab details
Measure the plan area, sanity-check the live project preview, set the slab thickness and quantity, then adjust procurement assumptions only if your supplier uses different values.
Slab measurement
Ordering & pricing
Advanced assumptions
Formula
Plan area × slab thickness × number of identical slabs = geometric concrete volume.
Contingency is applied to that volume before ready-mix rounding and bag conversion.
Concrete slab calculator FAQs
How much concrete do I need for a slab?
The calculator multiplies the plan area by slab thickness and by the number of identical slabs. It then shows the geometric volume, adds the contingency you selected and rounds the ready-mix quantity to your chosen order increment.
How many bags of concrete do I need?
Bag count is calculated from the adjusted concrete volume and the published yield of the bag product selected in Advanced assumptions. Different bag sizes and products have different yields, so the selected product matters.
Does the 4-inch default mean my slab should be 4 inches thick?
No. Four inches is only an editable starting value in the calculator. Slab thickness is a project-design decision and should come from the applicable plans, specification, engineer or code requirements.
Why is the ready-mix order rounded up?
Concrete suppliers commonly sell in set volume increments. JobsiteMeasure keeps the exact adjusted requirement visible, then rounds only the practical purchase quantity upward to the increment you selected.
Can I calculate an irregular concrete slab?
Yes. The shared area builder supports multiple added or subtracted shapes, so an irregular slab plan can be converted into one total area before thickness and quantity are applied.