How much concrete will 1 bag of cement make?

Quick Answer

One 80 lb bag of cement will make about 2 ft3 of concrete. This is enough concrete to cover a 2 ft x 1 ft area at 4 inches thick. The exact yield will vary based on the mix design.

How Much Concrete Does 1 Bag of Cement Make?

The amount of concrete that 1 bag of cement will make depends on the mix design used. Concrete is made up of cement, water, aggregates (sand and gravel), and sometimes other additives. The proportion of each ingredient in the mix determines the yield.

Here are some typical concrete mix designs and their yields per 80 lb bag of cement:

1:2:3 Mix

A basic concrete mix ratio is 1 part cement, 2 parts sand, and 3 parts aggregate (gravel). This is often referred to as a 1:2:3 mix.

For this mix:

  • 1 bag (80 lbs) of cement
  • 160 lbs sand (2 x 80 lbs cement)
  • 240 lbs gravel (3 x 80 lbs cement)

With this ratio, 1 bag of cement will make right around 0.5 cubic feet of concrete.

1:2:4 Mix

A richer concrete mix contains more aggregate. A 1:2:4 mix contains:

  • 1 bag (80 lbs) cement
  • 160 lbs sand
  • 320 lbs gravel

This mix has less void space than a 1:2:3 mix, so 1 bag of cement will yield approximately 0.45 cubic feet of concrete.

1:3:5 Mix

An even richer mix is 1:3:5:

  • 1 bag (80 lbs) cement
  • 240 lbs sand
  • 400 lbs gravel

With more sand and aggregate, 1 bag of cement makes about 0.4 cubic feet of concrete with a 1:3:5 mix.

High Strength Concrete Mix

For high strength concrete used in structural applications, the mix usually contains less aggregate and more cement. A typical high strength mix is something like 1:1:2.

With less space taken up by aggregate, 80 lbs of cement will yield around 0.3 cubic feet of high strength concrete.

Bags of Concrete vs Bags of Cement

It’s important to distinguish between bags of cement and bags of concrete. While 1 bag of cement makes about 0.4-0.5 ft3 of concrete, 1 bag of premixed concrete will make more, about 0.6 ft3.

This is because premixed concrete already contains the sand and gravel, the bag only needs water added. With cement, you have to mix in the aggregates yourself.

So 1 bag of concrete (premixed) yields about 25% more volume than 1 bag of cement.

Formulas for Concrete Yield from Cement

There are a couple ways to calculate the theoretical yield of concrete from a given quantity of cement:

Weight Method

Take the weight of cement and divide it by the weight of cement per cubic foot of concrete based on the mix design.

For example, with an 80 lb bag and a mix design calling for 500 lbs of cement per cubic yard (0.5 lb per ft3):

  • 80 lbs cement
  • 0.5 lb cement/ft3 concrete
  • 80 / 0.5 = 160 ft3 concrete

Volume Method

Determine the absolute volumes of each ingredient required for your mix design per cubic foot of concrete.

Add the volumes together to get the total volume for 1 ft3.

Divide the volume of cement from 1 bag by the total volume per ft3.

For example, with a 1:2:3 mix:

  • Cement: 1 ft3
  • Sand: 2 ft3
  • Gravel: 3 ft3
  • Total: 6 ft3 per ft3 concrete

An 80 lb bag of cement contains approximately 0.5 ft3 of cement.

0.5 ft3 cement / 6 ft3 total per ft3 concrete = 0.083 ft3 concrete per bag

So in theory, 1 bag would make 0.083 ft3 or roughly 1/12 ft3 of concrete.

Factors Affecting Yield

The actual yield of concrete produced from a bag of cement will be affected by a variety of factors:

Mixing Efficiency

Thorough mixing allows the cement to fully react with the water and creates a more homogeneous batter. Insufficient mixing can result in pockets of dry cement and lower overall yield.

Water Content

The water-cement ratio determines how hydrated the cement becomes. Too much water will make a weak concrete that shrinks as it dries. Too little water will prevent full curing and result in lower yield.

Aggregate Moisture

If the sand and gravel contain excess moisture, this effectively increases the water content, which can reduce yield.

Compaction

Proper compaction of the placed concrete eliminates air voids and settles the aggregates together. Poor compaction results in a lower density and less yield from the same quantity of cement.

Curing

Curing keeps concrete moist while it sets up to prevent cracking and develop strength. Inadequate curing can reduce ultimate yield.

Entrapped Air

Air bubbles that get trapped in the concrete take up space and lower yield. Using air entrainers purposely introduces tiny air pockets to increase freeze-thaw resistance. But too much unintended air content will greatly reduce yield.

Settling

Settling of heavier aggregates during concrete placement results in reduced yield compared to the theoretical volume.

Concrete Yield Table

Here is a table showing the approximate concrete yield from 1 bag (80 lbs) of cement based on some common mix ratios:

Mix Ratio Yield ft3 per 80 lb Bag
1:2:3 0.5
1:2:4 0.45
1:3:5 0.4
1:1:2 (high strength) 0.3

As you can see, the richer mixes with more aggregate produce lower concrete yields per bag of cement.

Concrete Coverage

Based on a yield of 0.4-0.5 ft3 per 80 lb bag, here is how much area that concrete will cover at different thicknesses:

Thickness Coverage
2 inches 5.3 – 6.7 ft2
3 inches 3.6 – 4.4 ft2
4 inches 2.7 – 3.3 ft2
5 inches 2.1 – 2.7 ft2
6 inches 1.8 – 2.2 ft2

For a 4 inch thick slab or footing, you can expect 1 bag to cover 2.5 – 3 ft2.

How Many Bags for a Specific Project?

You can estimate the number of 80 lb bags needed for a project based on the volume of concrete required.

Some examples:

Concrete Slab

For a 10×12 ft slab that is 4 inches thick:

  • Volume = Length x Width x Thickness
  • Volume = 10 x 12 x (4/12) = 4 ft3

With a yield of 0.5 ft3 per bag, you would need approximately 8 bags of cement.

Concrete Footing

For a strip footing 2 feet wide by 1 foot deep and 24 feet long:

  • Volume = Length x Width x Depth
  • Volume = 24 x 2 x 1 = 48 ft3

Using the same 0.5 ft3 per bag yield, you would need about 96 bags of cement.

Cylindrical Column

For an 8 inch diameter column that is 6 feet tall:

  • Volume = πr2h
  • r = 4 in = 0.33 ft
  • h = 6 ft
  • Volume = 3.14 x (0.33)2 x 6 = 2.1 ft3

So you’d need around 4 bags of cement to make this column.

Cost Estimate

The cost of the cement is a major component of the total cost for a concrete project.

As a rough estimate, you can figure each 80 lb bag of cement will cost $5-10, with an average of around $8 per bag at today’s prices.

So if you estimate needing 100 bags of cement based on your project dimensions and mix design, the cement cost could be estimated as:

  • 100 bags x $8/bag = $800

Keep in mind this is just the cost of the cement itself. You’ll also need to estimate expenses for aggregates, any additional admixtures, tools/equipment rental, labor, etc.

But starting with bags of cement required gives you a good ballpark idea of concrete costs. Just multiply the estimated bags by current bagged cement prices.

Mixing Concrete By Hand vs Premixed

For small DIY projects, it’s possible to manually mix all the ingredients for minor concrete pours. However for larger jobs or easier mixing, premixed concrete makes sense despite the higher cost per yard.

Here’s a quick comparison:

Mixing By Hand

– Purchase bags of cement then measure out aggregates
– Mix with a shovel on the ground or in a wheelbarrow
– Labor intensive
– Good for control over mix design
– Cost effective for small projects

Premixed Concrete

– Purchase ready mix by the cubic yard from a concrete supplier
– Delivered in a truck with mixer
– No measuring or hand mixing required
– Consistent mix and less labor for contractor
– Higher cost but ideal for larger jobs

So consider how much concrete you need and your labor resources. For a few bags, mixing by hand can save money but gets tiring for bigger projects. Having premixed delivered is easier but costs more per yard.

Concrete Mixer Capacity

Many homeowners and contractors use a concrete mixer to mix up bags of concrete for medium sized jobs.

The capacity of a concrete mixer determines how much concrete can be produced per batch.

Some typical concrete mixer capacities:

Mixer Size Capacity ft3
2 ft3 mixer 2 ft3
3.5 ft3 mixer 3.5 ft3
4 ft3 mixer 4 ft3
6 ft3 mixer 6 ft3
9 ft3 mixer 9 ft3

With a yield of around 0.5 ft3 per 80 lb bag, you can estimate how many bags each batch could handle:

  • 2 ft3 mixer – 4 bags cement
  • 3.5 ft3 mixer – 7 bags cement
  • 4 ft3 mixer – 8 bags cement
  • 6 ft3 mixer – 12 bags cement
  • 9 ft3 mixer – 18 bags cement

These capacities can help match the right size mixer to the amount of concrete you need to make for your jobs.

80 lb Bag Dimensions

Cement is commonly packaged in 80 lb paper sacks or bags. The bags are designed for stability during shipping and handling on palettes.

Here are the typical dimensions for 80 lb cement bags:

  • Length – Around 24-26 inches long
  • Width – Around 10-12 inches wide
  • Thickness – 4-6 inches thick

Knowing the dimensions can help when planning storage and transportation logistics. Bags are stacked and wrapped on shipping palettes for easy forklifting.

Be sure to check the actual bag dimensions from your supplier, as they can vary slightly by brand. The key is they are sized for stability when handling large volumes together.

Conclusion

– One 80 lb bag of cement will yield around 0.4 to 0.5 ft3 of concrete
– Actual yield depends on mix design proportions and mixing efficiency
– Richer mixes with more aggregate produce lower concrete yield per bag
– Estimate around 8 bags of cement for a 2.5-3 ft2 slab 4 inches thick
– Premixing improves productivity for larger jobs but costs more per yard
– Use bag yield estimates and project dimensions to calculate total cement needs
– Check mixer capacity when planning DIY mixing for medium jobs
– 80 lb cement bags are sized for stability when palletized for shipping

Knowing how to estimate yield from bags of cement allows proper planning of material quantities for concrete projects. This saves money by only purchasing the cement needed for the job. It also prevents shortages that could cause project delays. With the right volume calculations and yield estimations, you can be confident your concrete pours will go according to plan.

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