How Much Concrete for a 12×12 Slab?

4-inch slab estimate

Order quantity

1.956

yd³ of concrete

Includes 10% overage.

Base volume: 1.78 yd³

With 10% overage: 1.956 yd³

Confirm your supplier’s ordering increment. Bag counts below include the same overage.

Base volume (ft³)

cubic feet

60 lb bags

118

bags (inc. 10% waste)

80 lb bags

bags (inc. 10% waste)

Need a different size or thickness? Use the full calculator to get an estimate.

Calculate another size

Compare delivery for 1.956 yd³ with transporting and mixing 88 × 80 lb bags. Ask about minimum orders, access and delivery fees.

12 × 12 ft slab: thickness comparison

Same 144 ft² footprint, with 10% overage. Depths illustrate quantities, not structural recommendations. Bag yield: 0.60 ft³ per 80 lb bag.

Thickness	Base yd³	With overage yd³	80 lb bags
4 in	1.778	1.956	88
5 in	2.222	2.444	110
6 in	2.667	2.933	132
8 in	3.556	3.911	176

The 4-inch example needs 1.956 yd³ with overage. Confirm supplier order increments and delivery charges before ordering.

Calculation method

The formula is: Volume = Length × Width × Thickness. Convert thickness from inches to feet first, then divide by 27 to get cubic yards.

12 ft × 12 ft slab, 4 in thick; step by step

Step 1; Volume 12 × 12 × (4 ÷ 12) ft = 48 cu ft
Step 2; Cubic Yards 48 ÷ 27 = 1.78 cu yd
Step 3; Add 10% Waste 48 × 1.10 = 52.80 cu ft
Step 4; 60 lb Bags 52.80 ÷ 0.45 = ~118 bags
Step 5; 80 lb Bags 52.80 ÷ 0.60 = ~88 bags

Practical Tips for a 12×12 Slab

Use the specified thickness. The 4-inch figure here is a quantity example, not a structural recommendation.
Allow for overage. 10% is a starting allowance, not a universal specification. Allow for uneven ground and spillage.
Compact your sub-base first. 4–6 inches of gravel under the slab prevents settling and cracking.
Don't thin the mix with extra water. It makes mixing easier but weakens the concrete significantly.
Cure for at least 7 days. Keep the slab moist after pouring. This dramatically increases final strength.
Round up, not down. You cannot pour half a slab and come back; you'll get a visible cold joint.

Assumptions

QUIKRETE Concrete Mix technical data provides the 0.45 ft³ and 0.60 ft³ bag yields used here. Other mixes can have different yields.

◦ Slab dimensions: 12 ft × 12 ft at 4 inches thick. Changing thickness changes all totals.
◦ Concrete yield: 60 lb bags = 0.45 cu ft; 80 lb bags = 0.60 cu ft. Standard manufacturer figures.
◦ Waste factor: 10% applied. Increase to 15% for rough terrain or irregular shapes.
◦ Results are estimates only: Confirm quantities with your concrete supplier before ordering.

Questions

A 12×12 ft slab at 4 inches thick requires 48 cubic feet (1.78 cubic yards) of concrete. With a 10% waste factor, that's about 118 bags of 60 lb mix or 88 bags of 80 lb mix.

Compare the complete delivery quote with transporting and mixing 118 sixty-pound bags or 88 eighty-pound bags. Confirm supplier minimums, truck access and available mixing equipment.

Use the thickness specified for your project. The table above shows how quantity changes at different depths; it does not determine structural adequacy.

One cubic yard equals 27 cubic feet. At standard yields, you need about 60 bags of 60 lb mix or 45 bags of 80 lb mix per cubic yard; before adding a waste factor.

Setting, drying and curing are different processes. Follow the selected mix instructions and the project specification for curing, walking and loading times; weather and temperature affect them.