Concrete slab calculator
Enter your slab size to see how many cubic yards of concrete you need and how many 60 lb or 80 lb bags that is, with the math shown.
Concrete needed
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Enter your slab size.
The math, step by step
These are estimates. Bag yields come from the bag label and assume the recommended amount of water. Uneven or soft ground can eat up a lot more concrete than the math shows, so measure the depth in a few spots. Bags are heavy. Check your truck's payload before hauling them.
How we calculated this
Volume is length × width × thickness. Thickness is converted to feet (inches ÷ 12) or meters (centimeters ÷ 100) first. Cubic feet are divided by 27 to get cubic yards. Then the waste percentage is added on top.
Bags are rounded up to whole bags. A mixed 80 lb bag of standard concrete mix makes about 0.60 cubic feet. A 60 lb bag makes about 0.45 cubic feet. That's about 45 bags of 80 lb mix, or 60 bags of 60 lb mix, per cubic yard. High-strength and fast-setting mixes can yield a little differently, so check your bag.
For metric slabs, cubic meters are converted with 1 cubic meter = 35.31 cubic feet = 1.308 cubic yards.
Bags or ready-mix: under about 1 cubic yard, bags are usually the easy choice. From about 1 to 2 cubic yards, get a delivery quote and compare it with a day of mixing. Over about 2 cubic yards, ready-mix delivery is usually cheaper and much less work. Many suppliers add a short-load fee on small orders, so ask.
Sources and where they disagree
- Bag yields: Quikrete's Concrete Mix data sheet lists about 0.45 cubic feet for a 60 lb bag and 0.60 cubic feet for an 80 lb bag. A building supplier's guide gives the same 60 and 45 bags per yard. Some older forum posts quote 2/3 cubic foot for an 80 lb bag. This tool uses the lower 0.60 figure, so you're less likely to run short. Other brands and high-strength mixes can differ a little.
- Bags vs. ready-mix: no source gives an exact cutover, and they disagree. SlashGear compares about $270 in bags per cubic yard with roughly $300 to $350 for 2 yards of ready-mix before delivery fees. That points to delivery winning somewhere around 1 to 2 yards. The supplier guide above says small projects rarely need a truck, and that a full truck holds 9 to 10 yards. Short-load fees and minimum orders vary a lot by supplier, so get a quote.
- Waste: most guides suggest adding 5 to 10%. This tool starts at 10%.
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- Pickup truck loads – How many trips for gravel base, sand, or topsoil.
- Trailer loads: pavers, blocks, and stone – How much your trailer can safely carry per trip.
- Dump run – Hauling off old broken concrete.
Figures and sources last reviewed November 2026.