How many yards of concrete do I need for a 40×80 slab? To calculate the amount of concrete needed for a slab, you’ll need to multiply the length, width, and depth (thickness) of the slab in feet to get the volume in cubic feet, and then convert it to cubic yards. Assuming a typical slab thickness of 4 inches (which is 1/3 of a foot), here’s the calculation:

1. Calculate the volume in cubic feet: Volume = Length (feet) × Width (feet) × Depth (feet), Volume = 40 ft × 80 ft × (1/3) ft = 1067 cubic feet.

2. Convert the volume to cubic yards (since 1 cubic yard = 27 cubic feet): Volume (cubic yards) = 1067 cubic feet / 27 cubic feet per cubic yard ≈ 39.5 cubic yards

So, you’ll need approximately 39.5 cubic yards of concrete for a 40×80 slab with a thickness of 4 inches. Keep in mind that it’s a good idea to order a little extra concrete to account for variations and spillage.

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 40×80 (3200 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 40×80 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 40×80 slab**

**At 4″ thickness of slab**

To determine the how much concrete do I need for a 40×80 slab solve in following steps:-

Step 1 :- calculate the volume in cubic feet:- we have given 40×80 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′×80′×0.33′ = 1056 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 40×80 slab at 4 inch thick in cubic yard = 1056/27 = 39.11, round it 40 cubic yards.

Step 3 :- Add 10% extra :- considering extra 10% wastage during mixing and pouring, so 10% of 39.11 cubic yard = 3.911, add 39.11 + 3.911 = 43.021 cubic yard.

At 4 inches thickness, for a 40×80 slab, generally, you will need approximately 40 cubic yards or 1056 cubic feet of concrete. Always you should purchase 5 to 10% more premixed concrete than required. 4″ thick slab of 40×80 is ideal in normal load condition.

**How many yards of concrete do I need for a 40×80 slab at 5″ thick**

At 5 inches thickness, for a 40×80 slab, generally, you will need approximately 50 cubic yards or 1334 cubic feet of premixed concrete. Math’s calculation:- 1) square footage of slab = 40×80 = 3200 sq ft, 2) 5″ thickness in inches = 5÷12 = 0.416 feet, 3) volume of slab in cubic feet = 3200×0.416 = 1334 cubic feet, and 4) volume of slab in cubic yards = 1334÷27 = 50 cubic yards. Thus, you will need 50 cubic yards of premixed concrete for a 40×80 slab at 5 inches thick.

**How many yards of concrete do I need for a 40×80 slab at 6″ thick**

At 6 inches thickness, for a 40×80 slab, generally, you will need approximately 60 cubic yards or 1600 cubic feet of premixed concrete. Math’s calculation:- 1) square footage of slab = 40×80 = 3200 sq ft, 2) 6″ thickness in inches = 6÷12 = 0.5 feet, 3) volume of slab in cubic feet = 3200×0.5 = 2600 cubic feet, and 4) volume of slab in cubic yards = 1600÷27 = 60 cubic yards. Thus, you will need 60 cubic yards of premixed concrete for a 40×80 slab at 6 inches thick.

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**Cost estimate for a 40’×80′ slab**

A typical 40×80-foot (3,200 square foot) solid concrete slab may cost range between $12,800 and $25,600. For the most part, the average price of a concrete slab is $4 to $8 per square foot includes labour. A 40×80 slab is a 3,200 square foot. Using ready-mix concrete to cover 40×80 (3,200 sq ft) at a depth of 4″ to 6″-8″, the estimated cost is range between $12,800 to $25,600 (3,200× $4 = $12,800 or 3,200×$8 = $25,600).

**How much does a 40’×80’×4″ concrete slab cost?**

At 4 inches thick, a typical 40×80-foot (3,200 square foot) solid concrete slab may cost $12,800 includes labour. For the most part, the average price of a concrete slab is $4 per square foot at 4 inches thick. Based on the national average, a 40’×80’×4″ (3,200 square feet) concrete slab may cost about $12,800 (3,200 times $4 = $12,800).

**How much does a 40’×80’×5″ concrete slab cost?**

Pouring a concrete slab may cost between $4 and $8 per square foot. A 5″ thick slab will cost an average cost of $5 per square foot. Based on the national average, a 40’×80’×5″ (3,200 square feet) concrete slab may cost about $16,000 (3,200 times $5 = $16,000).

**How much does a 40’×80’×6″ concrete slab cost?**

Pouring a concrete slab may cost between $4 and $8 per square foot. A 6″ thick slab will cost an average cost of $6 per square foot. Based on the national average, a 40’×80’×6″ (3,200 square feet) concrete slab may cost about $19,200 (3,200 times $6 = $19,200).

**How much does a 40’×80’×8″ concrete slab cost?**

Pouring a concrete slab may cost between $4 and $8 per square foot. A 8″ thick slab will cost an average cost of $8 per square foot. Based on the national average, a 40’×80’×8″ (3,200 square feet) concrete slab may cost about $25,600 (3,200 times $8 = $25,600).

**Conclusion:-**

At 4 inches thickness, for a 40×80 slab, generally, you will need approximately 40 cubic yards or 1056 cubic feet of concrete. At 5″ thickness of 40×80 slab, 50 cubic yards or 1334 cubic feet of concrete will be necessary. At 6″ thickness of 40×80 slab, 60 cubic yards or 1600 cubic feet of concrete will be required.

If you have a 40×80 slab with 4 inches thick, you would need 40 cubic yards (1056 cubic feet) of ready-mix concrete which will cost range between $12,800 to $25,600 including labour.