Concrete Slab Calculator
Work out how much concrete a slab, footing, column pour or a batch of fence post holes needs: pick the shape, enter its real dimensions, and get the volume in cubic yards and cubic meters plus the number of pre-mixed bags to buy.
Result
This page opens the concrete calculator set up for a slab pour: enter the length and width in feet or meters, and the thickness in inches or centimeters, since slab thickness is almost always specified in the smaller unit even when the footprint is measured in the larger one. The calculator multiplies the three together to get volume.
A standard 4-inch slab is typical for a shed floor, a patio or a walkway, while driveways and structural slabs commonly go to 5 or 6 inches — small changes in thickness move the bag count more than most people expect, since volume scales linearly with it. A 10 × 10 ft slab at 4 inches is 33.33 ft³ (about 1.23 yd³); the same slab at 6 inches jumps to 50 ft³ (about 1.85 yd³), roughly 50% more material.
Once the volume is set, pick your bag size — 40, 60 or 80 lb pre-mix are the common retail sizes — and the calculator rounds up to a whole number of bags using the published typical yield for that size. Tick the waste checkbox to add 10% for spillage and an uneven subgrade before the bag count is calculated. Everything runs locally in your browser.