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Quikrete Bags Calculator

Enter your post hole dimensions and post size to get an exact bag count per post and for your entire fence project — 50 lb, 60 lb, and 80 lb bags all supported.

Quick Reference — 80 lb Bags Per Post

Hole Diameter	24" Deep	30" Deep	36" Deep
8" diameter	1 bag	2 bags	2 bags
10" diameter	2 bags	2 bags	3 bags
12" diameter	2 bags	3 bags	4 bags
14" diameter	3 bags	4 bags	5 bags

Use the calculator below for exact numbers based on your specific dimensions.

1Post and Hole Dimensions

Rule of thumb: Dig holes 3 times the post width in diameter. For a 4×4 post (3.5" actual) dig a 10-12" diameter hole. For a 6×6 post (5.5" actual) dig a 14-16" hole. Depth should be 1/3 to 1/2 the above-ground post height.

Post Size (quick select)

Hole Diameter

inches

Diameter of the dug hole — not the post

Hole Depth

ftin

Post Width (actual size)

inches actual(4×4 = 3.5", 6×6 = 5.5")

Number of Posts

Total posts in your project

2Bag Settings

Bag Size

Yield per bag from Quikrete product data sheets

Concrete Type

How to Use This Quikrete Bags Calculator

Follow these five steps to get an accurate material estimate for your fencing project.

Use the Post Size Quick-Select: Start by selecting your post type (e.g., 4x4 or 6x6). This will auto-fill the "Post Width" (actual size) and input a "Hole Diameter" based on industry-standard recommendations. You can adjust the hole diameter manually if necessary.
Set the Hole Depth: Adjust the hole depth based on your planned fence height and local frost lines. The standard rule of thumb is that fence post holes should be dug to a depth equal to one-third ($1/3$) to one-half ($1/2$) of the above-ground height of the post. Regardless of fence height, 24 inches is generally considered the absolute minimum depth for stability.
Enter Total Number of Posts: Input how many posts are in your fence run.
Select Bag Size: Choose which specific product you intend to buy. Note that while 80 lb bags generally provide the best financial value for larger projects, 50 lb Fast-Setting bags are significantly easier to handle if you are working solo.
Select Concrete Type: Choose between "Standard Mix" or "Fast-Setting." After clicking calculate, scroll down to the results to find specific installation instructions tailored to that concrete type.

The Formula

This calculator determines the net volume of concrete required by calculating the volume of the dug hole (cylinder) and subtracting the volume of the post being inserted (rectangular prism). All dimensional inputs (inches) are converted to feet for the final calculation.

Hole Volume = $\pi \times radius^2 \times depth$ (in feet)
Post Volume = $actualWidth^2 \times depth$ (in feet)
Bags Per Post = Net Volume / Bag Yield (rounded up to next whole bag)

We use specific product yield data provided by Quikrete for high-strength concrete mixes to ensure accuracy:

50 lb bag: Yields 0.375 cubic feet.
60 lb bag: Yields 0.45 cubic feet.
80 lb bag: Yields 0.60 cubic feet.

Frequently Asked Questions

How many 80 lb bags of Quikrete for a standard 4x4 fence post in a 10 inch hole at 24 inches deep?

You need **2 bags** (80 lb) for this specific scenario. While the raw net volume is roughly 0.925 cubic feet, one 80 lb bag only yields 0.6 cubic feet. You must purchase two bags, even though you won't use the full second bag.

Should I use Fast-Setting or standard Quikrete for fence posts?

For most homeowners, Fast-Setting Quikrete is superior for setting fence posts because it requires no mixing in a wheelbarrow. You set the post, pour the dry concrete from the bag into the hole, and add water on top. Standard concrete is slightly stronger and often cheaper, but requires labor-intensive pre-mixing before pouring.

How long to wait before attaching fence panels to Fast-Setting versus standard concrete?

If using Fast-Setting Quikrete, you can generally begin attaching fence panels or loading the post in **4 hours**. For standard concrete mixes, you should wait at least **24 to 48 hours** for the concrete to properly cure before subjecting the post to any load.

How much water to add per bag of Quikrete?

If using standard mix (mixed beforehand), you need approximately 3 quarts of water per 80 lb bag. If using Fast-Setting concrete (dry pour method), you don't use a specific measured amount; you pour water onto the dry mix until the mix is completely saturated.

Do Sakrete and other brands use the same bag yields as Quikrete?

Yes, generally. Pre-mix concrete is sold based on standard weights and industry-standard yields. An 80 lb bag of standard high-strength concrete mix will yield approximately 0.6 cubic feet, whether it is branded as Quikrete, Sakrete, or a generic store brand.

Do I need to mix Quikrete Fast-Setting or just pour it dry?

Just pour it dry. This is the intended "no-mix" method for setting fence posts or mailbox posts. You level the post, fill the hole with the dry Fast-Setting mix, then saturate it thoroughly with water. The water percolates through the dry mix, initiating the curing process without manual mixing.