Concrete & Masonry calculators
Slabs, footings, bags vs. ready-mix, blocks and walls.
About this calculator
The concrete slab calculator turns the size and thickness of a patio, pad, sidewalk or shed floor into cubic yards, the number of 40, 60 or 80 lb bags and a ready-mix order. It also suggests a control-joint layout and compares the cost of bags and ready-mix at your own prices.
How to measure
Measure the inside of your forms, not the outside of the boards, in feet. Use the circle shape for round pads. Enter the thickness you will actually pour. A slab that ends up a little thicker than planned needs noticeably more concrete, so check the depth in a few spots.
Before you start
- Order a little extra. NRMCA recommends at least 4 to 10% more than the measured volume to cover waste, spillage, form bulging and uneven subgrade.
- Bags are always rounded up to whole bags, and yields differ between products, so check the yield on the bag you buy.
- For ready-mix, ask about delivery or short-load fees, the minimum load, how close the truck can get and how much time you get to unload.
- Never pour onto frozen ground, snow or ice, and check thickness and driveway rules with your building department before you pour.