To calculate how many bags of concrete you need for an 12×20 slab, you’ll first need to determine the thickness of the slab you want. Standard concrete slabs are typically 4 inches thick, but you may want a different thickness depending on your project.

Concrete is a blended mix of Portland cement, sand, aggregate, water with approve ingredient. Cement is acts as binder or adhesive materials to bind the components of concrete all together to create workable paste. Sand acts as filler material that fills the voids and gap between components of concrete and remove the air. Aggregate, stone, or gravel used to strengthen the concrete strength.

To determine how many bags of premixed concrete you will need, divide the total cubic yards needed by the yield. Use the following yields per each bag size: A 40 pound bag yields 0.011 cubic yards, 60 pound bag yields 0.017 cubic yards, 50 pound bag yields 0.0138 cubic yards and 80 pound bag yields 0.022 cubic yards.

If you measure their yields in cubic feet, then yields per each bag size are following: A 40 pound bag yields 0.30 cubic feet, 60 pound bag yields 0.45 cubic feet, 50 pound bag yields 0.375 cubic feet and 80 pound bag yields 0.60 cubic feet.

To figure the amount of yards of concrete you will need, take the all measurements Length in feet, width in feet and thickness in inches. Convert thickness in feet. Multiply its length, width and thickness to get cubic footage. Multiply the total cubic footage by 0.037 to get total yards of concrete needed.

**How many bags of concrete do i need for a 12×20 slab**

The amount of concrete you need for a 12×20 slab depends on how thick it will be. So, for a 4-inch slab you’ll need 2.96 cubic yards (134 80lb bags), a 5-inch slab requires 3.70 cubic yards (167 80lb bags) and a 6-inch slab requires 4.44 cubic yards (200 80lb bags).

**How many bags of concrete do i need for a 12×20 slab at 3 inches thick**

At 3 inches thick, for a 12×20 slab you would need approximately either 100 80-Pound, 134 60-pound, or 200 40-pound bags of premixed concrete. If you measure in yards, 2.22 cubic yards (or 60 cubic feet) of concrete will be required.

**Let’s do calculation and proceeds following steps:**

1. Convert 3″ thickness in feet = 3/12 = 0.25′

2. Volume of concrete in cubic feet = 12 × 20 × 0.25 = 60 cubic feet

3. Volume of concrete in yards = 60 × 0.037 = 2.22 cubic yards.

4. Estimate No. of 80lb bags = 60/0.60 = 100 bags

5. Estimate No. of 60lb bags = 60/0.45 = 134 bags

6. Estimate No. of 40lb bags = 60/0.30 = 200 bags.

**How many bags of concrete do i need for a 12×20 slab at 4 inches thick**

At 4 inches thick, for a 12×20 slab you would need approximately either 134 80-Pound, 178 60-pound, or 267 40-pound bags of premixed concrete. If you measure in yards, 2.96 cubic yards (or 80 cubic feet) of concrete will be required.

**Let’s do calculation and proceeds following steps:**

1. Convert 4″ thickness in feet = 4/12 = 0.333′

2. Volume of concrete in cubic feet = 12 × 20 × 0.333 = 80 cubic feet

3. Volume of concrete in yards = 80 × 0.037 = 2.96 cubic yards.

4. Estimate No. of 80lb bags = 80/0.60 = 134 bags

5. Estimate No. of 60lb bags = 80/0.45 = 178 bags

6. Estimate No. of 40lb bags = 80/0.30 = 267 bags.

**How many bags of concrete do i need for a 12×20 slab at 5 inches thick**

At 5 inches thick, for a 12×20 slab you would need approximately either 167 80-Pound, 223 60-pound, or 334 40-pound bags of premixed concrete. If you measure in yards, 3.70 cubic yards (100 cubic feet) of concrete will be required.

**Let’s do calculation and proceeds following steps:**

1. Convert 5″ thickness in feet = 5/12 = 0.417′

2. Volume of concrete in cubic feet = 12 × 20 × 0.417 = 100 cubic feet

3. Volume of concrete in yards = 100 × 0.037 = 3.70 cubic yards.

4. Estimate No. of 80lb bags = 100/0.60 = 167 bags

5. Estimate No. of 60lb bags = 100/0.45 = 223 bags

6. Estimate No. of 40lb bags = 100/0.30 = 334 bags.

**How many bags of concrete do i need for a 12×20 slab at 6 inches thick**

At 6 inches thick, for a 12×20 slab you would need approximately either 200 80-Pound, 267 60-pound, or 400 40-pound **bags** of premixed concrete. If you measure in yards, 4.44 cubic yards (or 120 cubic feet) of concrete will be required.

**Let’s do calculation and proceeds following steps:**

1. Convert 6″ thickness in feet = 6/12 = 0.5′

2. Volume of concrete in cubic feet = 12 × 20 × 0.5 = 120 cubic feet

3. Volume of concrete in yards = 120 × 0.037 = 4.44 cubic yards.

4. Estimate No. of 80lb bags = 120/0.60 = 200 bags

5. Estimate No. of 60lb bags = 120/0.45 = 267 bags

6. Estimate No. of 40lb bags = 120/0.30 = 400 bags.

**Here’s are table for how much concrete do i need for a 12×20 slab:**

SL.no. |
Thickness |
Amount in Cubic Feet |
Amount in Cubic Yards |
#80 lb |
#60 lb |

1 | 2″ | 1.48 | 67 | 89 | 134 |

2 | 3″ | 2.22 | 100 | 134 | 200 |

3 | 4″ | 2.96 | 134 | 178 | 267 |

4 | 5″ | 3.70 | 167 | 223 | 334 |

5 | 6″ | 4.44 | 200 | 267 | 400 |

**Cost estimate for a 12×20 slab**

The cost of a 12×20 slab can vary based on factors like location, materials used, and labor costs. On average, you might expect to pay between $4 and $8 per square foot for a basic 4″ to 8″ thick concrete slab. Therefore, a 12’x20′ slab could cost roughly between $960 to $1,920, excluding additional expenses like site preparation or finishing touches.

**How much does a 12’×20’×4″ concrete slab cost?**

A 4″ thick slab will cost an average cost of $4 per square foot. So, based on the national average, a 12’×20’×4″ concrete slab may cost about $960 (since 240 times $4 = $960).

**How much does a 12’×20’×5″ concrete slab cost?**

A 5″ thick slab will cost an average cost of $5 per square foot. So, based on the national average, a 12’×20’×5″ concrete slab may cost about $1,200 (since 240 times $5 = $1,200).

**How much does a 12’×20’×6″ concrete slab cost?**

A 6″ thick slab will cost an average cost of $6 per square foot. So, based on the national average, a 12’×20’×6″ concrete slab may cost about $1,440 (since 240 times $6 = $1,440).

**How much does a 12’×20’×8″ concrete slab cost?**

A 8″ thick slab will cost an average cost of $8 per square foot. So, based on the national average, a 12’×20’×8″ concrete slab may cost about $1,920 (since 240 times $8 = $1,920).

**Conclusions:**

If you have a 12×20 slab with 4″ thick, you’ll need approximately either 134- 80lb, or 178- 60lb (2.96 yards, or 80 cubic feet) bags of premixed concrete which will cost an average of $576 including labour.