Concrete Square Footage Calculator
This concrete square footage calculator turns a known floor area into concrete. As a concrete area calculator it multiplies the square footage by the thickness to give cubic yards, cubic feet, weight, and bag counts. It is ideal when you already know the area of a slab, patio, or sidewalk and just need the volume — a handy sidewalk cement calculator too.
How to use this calculator
- Enter the area and pick square feet, yards, or meters.
- Enter the thickness of the slab.
- Add a waste allowance.
- Read the cubic yards for ready-mix or the bag count for hand mixing.
The formula
When you already know the area, volume is simply area times thickness. Convert the thickness to feet and divide by 27 for cubic yards:
Cubic yards = (Area ft² × Thickness ft) ÷ 27
Worked example. 100 square feet at 4 inches thick: 4 inches is 0.333 ft, so 100 × 0.333 = 33.3 cubic feet, which is 1.23 cubic yards — about 56 × 80 lb bags. One cubic yard covers roughly 81 square feet at this thickness.
Frequently asked questions
How do I calculate concrete from square footage?
Multiply the area in square feet by the thickness in feet to get cubic feet, then divide by 27 for cubic yards. Enter the area directly when you already know it.
How much concrete do I need for 100 square feet?
100 square feet at 4 inches thick is about 1.23 cubic yards (33.3 cubic feet), or roughly 56 × 80 lb bags.
How much concrete for a sidewalk?
A 3 ft wide, 30 ft long walk at 4 inches thick is 90 square feet — about 1.1 cubic yards. Sidewalks are usually poured 4 inches thick.
How many square feet does a yard of concrete cover?
One cubic yard covers about 81 square feet at 4 inches, 65 at 5 inches, and 54 at 6 inches thick.