Concrete bags calculator
Turn hole diameter, depth and the number of holes into a bag count for 50, 60 and 80 pound mixes, with the volume math shown.
Concrete bags needed
Enter your measurements and the result updates as you type.
Overview
Two numbers decide how much mix a set of holes needs: the volume of each hole and the yield of the bag you buy. This calculator treats each hole as a cylinder, converts the total to cubic feet, and then to bags by the published yield for 50, 60 and 80 pound mixes.
Yields differ per bag size (0.375, 0.45 and 0.6 cubic feet respectively), and bag counts round up, so the "right" answer is whichever whole number of bags is on the shortlist for your hole set.
Common mistakes
- Forgetting to convert inches to feet before multiplying, which is the classic order-of-magnitude error in concrete math.
- Using a bag "coverage" number meant for topping or patio slabs on post holes, which have completely different depth profiles.
- Rounding bag totals down to the next whole bag because the decimal is close, leaving the number of holes half set.
Related calculators
- Fence post concrete calculator Work out how many bags of concrete mix each fence post footer needs, accounting for the post itself, based on hole and post dimensions.
- Fence post calculator Calculate line posts, corner posts and end posts from run length and spacing, with concrete for each post included in the take-off.
- Fence cost calculator Estimate total fence cost from run length, height and your local material and labor rates, with the budget math shown.
Related reading
In-depth guides
Frequently asked questions
How many bags of concrete are in a 10 by 24 inch hole?
A 10 inch by 24 inch hole is about 1.09 cubic feet of volume. At 0.45 cu ft per 60 lb bag that is 2.4 bags, so 3 bags set the hole; at 0.6 cu ft per 80 lb bag it is 1.8 bags, so 2. The calculator does this for any size you enter.
What is the formula for bags of concrete needed?
Find each hole's volume as pi times the radius squared times the depth (in feet: inches divided by 12 for diameter and for depth), multiply by the number of holes, then divide the total cubic feet by the yield of your bag size and round up.
Does the formula subtract the post?
Not by default: this calculator treats a set of empty holes, which is the right model for filling holes or when the post diameter is not set by the concrete volume. The post concrete calculator subtracts a centered post when you need footer volume with a post inside.
Which bag size is the cheapest way to fill my holes?
Compare the cost per cubic foot across sizes at your store: 80 lb bags yield 0.6 cu ft, 60 lb bags 0.45 cu ft and 50 lb bags 0.375 cu ft, so the bigger bags are usually (not always) the better value per yard once quickset is off the table.
How many bags for a deck post or a fence corner footer?
Run the same model at a wider hole: corners commonly get a larger diameter, lifting both the cubic feet and the bag total. Enter the corner-hole size and multiply by the corner count to keep a spread footer honest.
How much concrete is in a 60 lb bag?
60 lb bags of standard mix yield about 0.45 cubic feet of cured concrete. That is the conversion this calculator uses for per-bag totals across the 60 lb shortlist.
Do fast-setting mixes have the same yield?
Approximate yes: published yields for quickset and standard mix are close for the same bag weight, so this calculator's bag counts hold for either. Only the working time changes, which no calculator can spend for you.
Why are bag counts rounded up?
A bag is sold as a whole unit, so the real purchase list has to be whole numbers and one extra bag is cheaper insurance than one missing mid-install. The result shows 2.4 bags as 3 bags of 60 lb, which is what lands in the cart.