How many yards of concrete do I need for a 40×30 slab | how much concrete do i need for a 40×30 slab at 4″, 5″ and 6″ 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 40×30 (1200 sq ft) slab at 4 inch, 5 inch or 6 inch thick.

Generally standard thickness of slab is 4 inch thick in normal conditions, if 40×30 slab have heavy traffic and heavy load, you should take depth 5 or 6 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.

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**How many yards of concrete do I need for a 40×30 slab**

**At 4″ thickness of slab**

To determine the how much concrete do I need for a 40×30 slab solve in following steps:-

Step 1 :- calculate the volume in cubic feet:- we have given 40×30 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 = 40′×30′×0.33′ = 396 cubic feet.

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 yards of concrete you needed for 40×30 slab at 4 inch thick in cubic yard = 396/27 = 14.6, round it 15 cubic yards.

Step 3 :- Add 10% extra :- considering extra 10% wastage during mixing and pouring, so 10% of 14.6 cubic yard = 1.46, add 14.6 + 1.46 = 16 cubic yard.

At 4 inches thickness, for a 40×30 slab, generally, you will need approximately 15 cubic yards or 396 cubic feet of concrete. Always you should purchase 5 to 10% more premixed concrete than required. 4″ thick slab of 40×30 is ideal in normal load condition.

**How many yards of concrete do I need for a 40×30 slab at 5″ thick**

At 5 inches thickness, for a 40×30 slab, generally, you will need approximately 19 cubic yards or 499 cubic feet of premixed concrete. Math’s calculation:- 1) square footage of slab = 40×30 = 1200 sq ft, 2) 5″ thickness in inches = 5÷12 = 0.416 feet, 3) volume of slab in cubic feet = 1200×0.416 = 499 cubic feet, and 4) volume of slab in cubic yards = 499÷27 = 19 cubic yards. Thus, you will need 19 cubic yards of premixed concrete for a 40×30 slab at 5 inches thick.

**How many yards of concrete do I need for a 40×30 slab at 6″ thick**

At 6 inches thickness, for a 40×30 slab, generally, you will need approximately 23 cubic yards or 600 cubic feet of premixed concrete. Math’s calculation:- 1) square footage of slab = 40×30 = 1200 sq ft, 2) 6″ thickness in inches = 6÷12 = 0.5 feet, 3) volume of slab in cubic feet = 1200×0.5 = 600 cubic feet, and 4) volume of slab in cubic yards = 600÷27 = 23 cubic yards. Thus, you will need 22 cubic yards of premixed concrete for a 40×30 slab at 6 inches thick.

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**Conclusion:-**

At 4 inches thickness, for a 40×30 slab, generally, you will need approximately 15 cubic yards or 396 cubic feet of concrete. At 5″ thickness of 40×30 slab, 19 cubic yards or 499 cubic feet of concrete will be necessary. At 6″ thickness of 40×30 slab, 23 cubic yards or 600 cubic feet of concrete will be required.