Concrete Slab Calculator
Estimate cubic yards, slab weight, and 40/60/80-lb bag counts in seconds. Preview your pour in 3D, stack sections, and plan with less waste.
Concrete Slab Formula, 4-Inch Coverage, and Bag Math
A strong concrete slab calculator page should answer more than one question. Users want the slab formula, cubic feet to cubic yards conversion, a 4-inch slab rule of thumb, and realistic bag math before they commit to bagged mix or ready-mix. This page keeps those slab decisions close to the calculator so you can measure once and order with more confidence.
Volume formula
For a rectangular slab, multiply length × width × thickness to get cubic volume. If thickness is entered in inches, convert it first so your slab math stays consistent.
Yards conversion
Concrete is commonly ordered in cubic yards, so once you have cubic feet, divide by 27 to get the number suppliers expect.
4-inch quick rule of thumb: about 81 sq ft per cubic yard
A 4-inch slab covers roughly 81 square feet per cubic yard, which makes it a fast sense-check for patios, pads, and small walkways before you rely on the final total.
Bag logic used by this calculator
Bag counts follow the same logic used in the tool: about 0.3 ft³ per 40-lb bag, 0.45 ft³ per 60-lb bag, and 0.6 ft³ per 80-lb bag, rounded up so you do not under-order.