Figuring out how much concrete you need for a project can seem complicated, but it’s actually pretty straightforward once you know the basics. Here’s a step-by-step guide to calculating the number of concrete bags required for your particular project.

## Quick Answers

Here are some quick answers to common questions about calculating concrete needs:

– Estimate 1 bag of concrete covers about 0.6 cubic feet volume (60 lbs bag)

– Most concrete bag labels specify yield in cubic feet

– Measure the volume (length x width x depth) of your project in feet to estimate needed bags

– Add 10-20% extra for wastage and overage

– Consider concrete thickness (usually 4-6 inches) based on project type

– Use an online concrete calculator for complex shapes

## Step 1: Determine the Volume of Concrete Needed

First, you need to calculate the total volume of concrete required for your project. This will depend on the size and scope of what you are building or repairing. Here are some things to consider:

- Measure the length, width and depth of the area to be concreted. Multiply L x W x D to get the total volume in cubic feet.
- Check the thickness required – this is usually between 4-6 inches for most projects like slabs, footings and foundations. The thickness impacts total volume.
- For complex shapes like curved walls or Odd forms, break it down into basic geometric shapes like squares, circles and triangles.
- Consider any gravel or substrate that will sit under the poured concrete and adjust depth accordingly.
- Add approximately 10% extra volume to account for wastage or overpour on site.

Let’s look at an example:

You need to pour a concrete slab that will be 20 ft long x 10 ft wide x 4 inches thick. The basic volume would be:

Length: 20 ft

Width: 10 ft

Thickness: 0.33 ft (4 inches converted to feet)

Volume: 20 x 10 x 0.33 = 66 cubic ft

Now we add 10% for wastage/overpour = 66 x 0.1 = 6.6 cubic ft

Total volume needed = 66 + 6.6 = 72.6 cubic ft

## Step 2: Estimate Concrete Bag Requirements

Now that you know the total concrete volume needed, you can estimate the number of bags required. Here’s how:

- Check the yield on the concrete bag – this tells you volume per bag (usually 0.5-0.75 cubic ft).
- Divide your total volume by the per bag yield to get approximate bags needed.
- Round up to the nearest whole bag for purchase – you can’t buy part bags!
- Consider adding 10-20% extra bags for wastage, overpour or returns.

Let’s continue our example:

The concrete bags specify a 0.6 cubic ft yield per bag.

Our total volume calculated is 72.6 cubic ft.

Bags needed = Volume / Yield per bag

= 72.6 cu ft / 0.6 cu ft per bag

= 121 bags

Rounding up gives us 125 bags for the project. Add 10% for overage and we get 138 bags to purchase.

## Step 3: Check Concrete Coverage Area

It’s useful to also estimate the coverage area a given amount of concrete achieves. This helps plan the pour and finish the slab properly. Some typical coverage guidelines are:

- 1 cubic yard of concrete covers 100-110 sq ft area at 4 inches thick
- 1 bag of concrete covers approx 8-10 sq ft area at 4 inch thickness
- Double the depth to double the coverage area

So for our example with 138 bags:

At 8 sq ft per bag that gives: 138 x 8 = 1104 sq ft coverage area

Our slab is 20 x 10 = 200 sq ft

So we have plenty of concrete to complete the pour and finish properly.

## Step 4: Order and Pick Up Concrete

Now that you’ve calculated the concrete requirements for your project, you can place an order and arrange pickup or delivery. Some tips for ordering:

- Order early – at least 48 hours ahead – to ensure stock is available.
- Choose your concrete mix – common are 3000 or 3500 psi standard mixes.
- Specify number of bags or cubic yards needed.
- Discuss delivery date/time and any special instructions.
- Make sure you have equipment/help ready for unloading.

When collecting bags yourself:

- Make sure vehicle is suitable for heavy load.
- Load carefully and evenly distribute weight.
- Secure bags tightly so they don’t shift and spill.
- Cover load with tarpaulin for weather protection.

## Other Factors When Ordering Concrete

Some other considerations when purchasing concrete include:

- Slump – a measure of concrete workability. Standard is 4 inches.
- Air entrainment – for freeze/thaw resistance.
- Reinforcement – rebar, fiber mesh for strength.
- Special exposure – sulfate resistant concrete etc.

Discuss these with your concrete supplier to ensure you get the right mix for the job.

## Estimating Concrete via Online Calculators

For complex curved, circular or irregular shaped projects, an online concrete calculator can be useful. You input the dimensions and it computes the volume and bags required.

Some popular concrete calculators include:

These tools allow you to handle curved walls, odd shapes, tube footings and other complex projects with ease.

## Key Takeaways

Here are some key tips to remember when estimating concrete needs:

- Calculate total volume in cubic feet – Length x Width x Thickness
- Allow 10% extra volume for wastage and overpour
- Check yield per bag on the concrete label
- Divide total volume by yield per bag to get bags required
- Round up and add overage bags for safety
- Plan for adequate coverage area based on slab size
- Order early and discuss mix, delivery etc. with supplier
- Use online calculators for complex shaped projects

With the techniques above, you can accurately estimate your concrete requirements. Keep in mind it’s better to have leftover bags than run short halfway through a pour. Calculate carefully and add a safety margin of extra concrete. This will ensure you can finish the project with no problems.

## Frequently Asked Questions

### What size bag of concrete should I use?

The most common bag sizes for concrete are:

- 60 lb bag – Yields 0.5 cubic ft
- 80 lb bag – Yields 0.65-0.7 cubic ft
- 94 lb bag – Yields 0.75 cubic ft

For most DIY projects, the 60 lb or 80 lb bags are preferred for easier handling.

### How many bags of concrete per cubic yard?

There are approximately 28-30 x 80 lb bags of concrete per cubic yard. Here is the full breakdown:

- 60 lb bags – 54 bags per cubic yard
- 80 lb bags – 36 bags per cubic yard
- 94 lb bags – 30 bags per cubic yard

So 1 yard = 36 x 80 lb bags is a good rule of thumb.

### How long does bagged concrete last?

Bagged concrete can last up to 12 months in sealed, dry storage. The bags should be stacked flat off the ground and protected from moisture. Discard any bags that are ripped or hardened.

### What PSI rating is best for concrete?

3000-4500 PSI concrete is suitable for most residential applications like foundations, footings, slabs and walkways. Higher strengths up to 5000 PSI may be used for driveways, garage slabs and patios.

## Conclusion

Estimating concrete needs for your DIY project doesn’t have to be confusing. By following the simple steps outlined here, you can determine exactly how many bags of concrete are required. Always calculate the volume carefully, add extra for wastage, and confirm coverage area based on slab size. With the right planning and preparations, you can ensure you purchase the perfect concrete quantity for a successful pour.