Estimate concrete for fence posts, deck posts, mailbox posts, and small round post holes. Enter hole size, post size, quantity, and waste to get concrete per hole, cubic yards, 60 lb bags, and 80 lb bags.
6 holes, 12 in diameter x 30 in concrete depth
Hole depth and width should follow frost, soil, fence, deck, gate, product, inspection, or code requirements. This only estimates concrete volume around the post.
Recent post hole estimates will appear here.
Post hole concrete estimates stay local. This is material volume math, not a code or load check.
Inputs and recent answers stay in this browser tab and are not sent to a server.
Estimate concrete bags for fence posts.
Plan concrete for deck support holes.
Subtract post volume from round hole volume.
Compare hole sizes before buying concrete.
11.52 ft3 total, about 0.43 yd3, 20 eighty-pound bags
11.52 ft3 total, about 0.43 yd3, 20 eighty-pound bags
0.96 ft3, about 2 eighty-pound bags
9.24 ft3 total, about 16 eighty-pound bags
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Plain-language answers about when to use the tool, what it does with your inputs, what to double-check, and how privacy works.
Use it when your task matches one of these common needs: Estimate concrete bags for fence posts. Plan concrete for deck support holes. It works best when you already know the measurements, amounts, units, or options the page asks for.
In plain language: The calculator finds round hole volume, subtracts the round post volume inside the hole, multiplies the net fill by the number of holes, adds waste, converts to cubic yards, and rounds 60 lb and 80 lb bag counts up. The examples on the page are there so you can compare your inputs with a worked example before copying the answer.
Hole diameter: the width across the round hole in inches. Hole depth: the depth filled with concrete in inches. Post diameter: the round-equivalent width of the post that takes up space inside the hole. Quantity: how many matching holes to estimate. Waste percent: extra concrete for uneven holes, overfill, spillage, and ordering cushion.
Read the headline estimate first, then check the material, waste, coverage, and unit lines. For project tools, the supporting lines are often the difference between a rough idea and a list you can actually shop from.
Post depth, hole width, gravel base, frost depth, uplift, gate loads, deck loads, soil, drainage, bracing, product instructions, and local code can change what you actually need. Also check the unit, scale, mode, and result limit because small input changes can change the answer.
The post occupies part of the hole, so concrete only fills the space around it. Subtracting the post keeps the estimate closer than treating the whole hole as concrete.
Use the closest equivalent diameter for a rough estimate or calculate the square post area separately. For big jobs, a contractor takeoff is safer.
With a 4 inch post in each hole and 10% waste, the default example needs about 11.52 cubic feet of concrete total, or 20 eighty-pound bags.
The default 12 inch by 30 inch hole with a 4 inch post uses about 3.3 eighty-pound bags per hole after 10% waste, so six holes round up to 20 bags total.
Yes if the post sits in the concrete while the hole is filled. The post takes up space, so subtracting it keeps the bag count closer than filling the whole hole as solid concrete.
A square post does not subtract perfectly with a round diameter field. For a quick estimate, enter the post width as the diameter. For important or expensive work, calculate the square post volume separately.
No. If your plan uses gravel at the bottom, subtract that depth from the concrete depth or estimate the gravel separately.
Use it only for the concrete volume around the post. Deck and gate posts can need deeper holes, wider holes, bracing, uplift checks, frost protection, and inspections.
No. The calculator uses the depth you enter. Fence height, soil, frost line, wind, gate load, deck load, and local code can all change the depth.
Concrete bags are sold as whole bags. The calculator rounds up after waste because running short during a post pour is worse than having a little left over.
Yes, but use the yield printed on the product bag if it differs from the common 60 lb and 80 lb bag assumptions used by this calculator.
No. The calculator runs in your browser tab. Your recent answers stay only on the page while you use it, and they are not sent to a server.