How Many Bags of Concrete Do You Need for a 10x10 Slab?
A 10 ft by 10 ft slab at 4 inches thick is one of the most common small concrete projects. Here is the exact quantity, the bag count, and how the numbers change with thickness and waste.
A 10 ft by 10 ft slab at 4 inches thick is one of the most common small concrete projects: a patio, a shed base, a hot-tub pad. The quantity is small enough that bagged mix is realistic, but large enough that running short mid-pour is a real risk. This post works the numbers from the geometry up, then shows how thickness and waste change the answer.
The geometry
Volume equals length times width times thickness, with the thickness converted to feet. For a 10 ft by 10 ft slab at 4 in thick:
10 ft × 10 ft × (4 in ÷ 12) = 100 ft² × 0.333 ft = 33.33 ft³.
Dividing by 27 gives 1.23 cubic yards. That is the base geometric quantity — the number the drawing could defend.
How many bags?
An 80 lb bag of concrete mix typically yields about 0.60 ft³. Dividing 33.33 ft³ by 0.60 gives 55.6 bags, which rounds up to 56 bags. A 60 lb bag yields about 0.45 ft³ and would require 74 bags. Always use the yield printed on the actual bag, since yields vary by product and mix design.
Adding waste
A tight, well-formed pour on a prepared base can get by with 5 % waste. A hand-mixed pour with wheelbarrows and an uneven subgrade needs 10 % to 12 %. At 10 % waste, 33.33 ft³ becomes 36.67 ft³, which is 61 bags at 0.60 ft³ per bag. The difference between 56 and 61 bags is the cost of a short pour, so the waste allowance is worth taking seriously.
What if the thickness changes?
Volume scales directly with thickness. A 10 ft by 10 ft slab at 5 in thick is 41.67 ft³, or about 70 bags at 0.60 ft³. At 6 in thick it is 50 ft³, or 84 bags. Going from 4 in to 6 in adds 50 % to the material, which is why thickness is the single most important input on a small slab and should be verified against the actual base, not assumed.
Ready-mix or bags?
At 1.23 yd³, this slab sits right at the edge where ready-mix becomes competitive. A short-load ready-mix order of 1.5 yd³ plus a delivery fee often costs less than 60 bags plus the labor of mixing, but the crossover depends on local prices and the supplier's short-load minimum. Run both numbers through the concrete cost calculator before deciding.
Practical notes
Measure the slab inside the forms, not the stake line. Prepare and compact the base before pouring. Order one or two extra bags beyond the calculated count for defects and spillage. Do not apply a waste percentage twice — once in the thickness and once in the percentage field. And remember that a quantity estimate is not a structural design: reinforcement, subgrade capacity and code requirements are separate decisions.