How many bags of concrete do I need for a 3×6 slab? To calculate how many bags of concrete you need for a 3×6 slab, you’ll first need to determine the thickness of the slab you want. Typically, concrete slabs are poured at a thickness of 4 inches (0.333 feet) for residential use. Here’s how you can calculate it:

1. Calculate the volume of the slab:

Volume = Length x Width x Thickness

Volume = 3 feet x 6 feet x 0.333 feet = 6 cubic feet.

2. Convert the volume to cubic yards (since concrete is typically sold in cubic yards):

6 cubic feet ÷ 27 (cubic feet in a cubic yard) = 0.222 cubic yards

3. Now, you need to convert the volume to the number of bags of concrete. A typical 80-pound bag of concrete mix yields about 0.6 cubic feet of concrete. So, you can calculate the number of bags needed by dividing the volume by the yield per bag: 6 cubic feet ÷ 0.6 cubic feet per bag = 10 bags. So, you would need approximately 10 bag of concrete for a 3×6 slab if it’s 4 inches thick.

Concrete ready mix made of blended mix of Portland cement, sand gravel and other approved ingredient, generally, dry ready mix concrete are available in different bag size and weight condition like 40lb, 60lb bag, 80lb bag, 90lb bag and etc.

Regardless of size you need to calculate the volume of concrete in cubic yard before ordering the mixed concrete. Volume is calculated by multiplying length, width and depth of slab. In this article we have to calculate required quantity of concrete in cubic yard for a 3×6 (18 sq ft) slab at 4 inch thick.

Weight of Ready mix concrete in dry condition is about 133 lbs per cubic foot, 3600 lbs per cubic yard, or 2136 kg per cubic meter. The weight of concrete is determined by its density, which can vary based on the amount of aggregate, water, and air in the mix.

In United States, based on Imperial and US customary measurement system, 1 cubic yard is unit of measurement of volume represented by 3 feet long by 3 feet wide by 3 feet depth (3’×3’×3′ = 27 cubic feer), so 1 cubic yard is equal to 27 cubic feet.

**How many bags of concrete do I need for a 3×6 slab**

To determine how many bags of concrete you will need, divide the total cubic yards or cubic feet needed by the yields.

We know concrete bag available in 40lb, 60lb, 80lb and 90lb. 40lb bag of concrete yields about 0.011 cubic yards or 0.30 cubic feet.60lb bag of concrete yields about 0.017 cubic yards or 0.45 cubic feet. 80lb bag of concrete yields about 0.022 cubic yards or 0.60 cubic feet and 90lb bag of concrete yields about 0.025 cubic yards or 0.68 cubic feet.

**At 4 inches thick**

To determine the how many bags of concrete do I need for a 3×6 slab solve in following steps:-

Step 1 :- calculate the volume in cubic feet:- we have given 3×6 slab (length × width), consider it is 4 inch thick, 4 inch = 0.33 feet, to determine the volume of slab, you need to multiply all dimensions, such that = 3′×6′×0.33′ = 5.94 cubic foot.

Step 2 :- converting cubic feet into cubic yard:- now converting into cubic yard, you should divide it by 27, because 1 cubic yard = 27 cubic foot, so volume of concrete you needed for 3×6 slab at 4 inch thick in cubic yard = 5.94/27 = 0.22 cubic yard.

Step 3 :- Add 10% extra :- considering extra 10% wastage during mixing and pouring

Step 6:- No. of bags of 80 lb concrete = 5.94 ÷ 0.60 = 10 bags, no. of bags of 60 lb concrete = 5.94 ÷ 0.45 = 14 bags, and no. of bags of 40 lb concrete = 5.94 ÷ 0.30 = 20 bags.

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**How many bags of concrete do I need for a 3×6 slab**

At 4 inches thick, for a 3×6 slab, generally, you will need either Fourteen- 60 lb or Ten- 80 lb or Twenty- 40 pound bags of premixed concrete. Math’s calculation:- 1) square footage of slab = 3×6 = 18 sq ft, 2) 4″ thickness in inches = 4÷12 = 0.33 feet, 3) volume of slab in cubic feet = 18 ×0.33 = 5.94 cubic feet, and 4) No. of 60lb bags = 5.94÷0.45 = 14 bags, no. of 80lb bags = 5.94÷0.60 = 10 bags, and no. of bags of 40 lb concrete = 5.94÷ 0.30 = 20 bags.

**How much concrete do i need for a 3×6 slab**

At 4″ thick, for a 3×6 slab, generally, you will need 0.22 cubic yards or 5.94 cubic feet or either 14- 60 lb or 10- 80 lb or 20- 40 pound bags of premixed concrete. Always you should purchase 5 to 10% more premixed than required.

**How many yards of concrete do I need for a 3×6 slab**

At 4″ thick, for a 3×6 slab, generally, you will need approximately 0.22 cubic yards of premixed concrete. Math’s calculation:- 1) square footage of slab = 3×6 = 18 sq ft, 2) 4″ thickness in inches = 4÷12 = 0.33 feet, 3) volume of slab in cubic feet = 18×0.33 = 5.94 cubic feet, and 4) volume of slab in cubic yards = 5.94÷27 = 0.22 cubic yards. Thus, you will need 0.22 cubic yards of premixed concrete for a 3×6 slab at 4 inches thick.

**How many cubic feet of concrete do I need for a 3×6 slab**

At 4 inches thick, for a 3×6 slab, generally, you will need approximately 5.94 cubic feet of premixed concrete. Math’s calculation:- 1) square footage of slab = 3×6 = 18 sq ft, 2) 4″ thickness in inches = 4÷12 = 0.33 feet, 3) volume of slab in cubic feet = 18×0.33 = 5.94 cubic feet. Thus, you will need 5.94 cubic feet of premixed concrete for a 3×6 slab at 4 inches thick.

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**Conclusions**:-

At 4 inches thick, for a 3×6 slab you typically need fourteen 60-pound bags, ten 80-pound bags, or twenty 40-pound bags, or 5.94 cubic feet or 0.22 cubic yards of ready-mix concrete. Always buy 5-10% more ready-made mix than you need.