Concrete & Masonry
Slabs, footings, columns and bag counts. The biggest cluster in the trades.
Concrete
Slabs & patios
Calculate how many cubic yards of concrete and how many 60 lb or 80 lb bags you need for a slab, patio or driveway.
Rebar
Slab reinforcement
Calculate how much rebar a concrete slab needs — bar count, total linear feet, number of 20 ft sticks to buy and the steel weight — from the slab size, grid spacing and bar size.
Concrete Bags
Small pours
Find out how many bags of pre-mixed concrete you need for a given volume, by bag size (40, 60 or 80 lb).
Concrete & Masonry guides
The formulas, conversions and how-tos behind these calculators.
How Many 80 lb Bags of Concrete Are in a Yard?
You need 45 × 80 lb bags to make one cubic yard of concrete. Here's the math and the counts for 60 and 40 lb bags too.
How Much Does a Bag of Concrete Weigh?
Concrete comes in 40, 50, 60 and 80 lb bags. The number on the bag is its dry weight before you add water.
How Thick Should a Concrete Slab Be?
4 inches is standard for patios and walkways; driveways need 5–6 inches. A thickness chart by application.
How Much Does Concrete Cost Per Yard?
Ready-mix concrete runs about $125–$165 per cubic yard delivered, before short-load and other fees.
How Many Square Feet Does a Yard of Concrete Cover?
One cubic yard covers 81 ft² at 4 inches thick. Coverage depends entirely on slab thickness.
How Much Rebar Do I Need for a Concrete Slab?
Work out rebar for a slab: lay a two-way grid at 12–18 in on center, count the bars each way, total the length and add ~10% for laps. Worked example inside.
Rebar Size & Spacing Chart (Weight, Diameter & Grid)
Rebar sizes #3–#6 with diameter and weight per foot, plus the on-center spacing to use by application. A quick reference for sizing a slab mat.