How Many Concrete Bags For Fence Posts

Planning how many concrete bags for fence posts starts with one honest number: how much material you actually need. This page walks through that number using the typical spacings, waste allowances and bag counts in our material data — and it starts with a warning worth taking seriously. The result here is an estimate, not a guarantee: board sizes, pack sizes and prices vary by brand, product line and region, and the label on the product you buy governs. A board that looks identical on two shelves can be a different width or length, and a deck or fence that measures the same on paper can need very different amounts of material once the cuts, the joist spacing and the waste are counted. That is why every figure below is shown as a range, and why the calculator on this page asks for your measurements instead of handing you a single magic number.

The second thing to know is that decking is counted in square feet plus the typical 5–10% waste allowance, and fencing is counted in linear feet with posts typically spaced 8 ft apart. Joists are typically spaced 12–16 in apart, screws run 2 per board per joist, and concrete per fence post is typically 1–2 50 lb bags. A cubic yard is 27 cubic feet, and an 80 lb bag of concrete yields about 0.6 cubic feet, so about 45 80 lb bags make a cubic yard. The rest of this page works through the calculation, a full worked example, cost guidance and the steps to measure, order and check your materials before you start.

How the calculation works

Concrete for fence posts is counted per post, not per cubic yard. Our material data gives a typical 1–2 50 lb bags per post, or about half to one 80 lb bag per post. For larger footings the maths changes: a cubic yard is 27 cubic feet, an 80 lb bag yields about 0.6 cubic feet, so about 45 80 lb bags make a cubic yard, and a 60 lb bag yields about 0.45 cubic feet, so about 60 60 lb bags make a cubic yard. Add the typical 10% extra for waste and uneven ground. The calculator gives ranges, because hole size and depth vary by soil and by local frost depth.

Worked example: concrete for 16 fence posts

Step 1 — count the posts. A 120 ft fence with posts typically spaced 8 ft apart needs 120 ÷ 8 + 1 = 16 posts.

Step 2 — bags per post. Concrete per fence post is typically 1–2 50 lb bags, or about half to one 80 lb bag. 16 posts × 1–2 bags = 16–32 50 lb bags.

Step 3 — check the hole. A deeper or wider hole needs more concrete, so measure your hole size before you buy. Result: about 16–32 50 lb bags for 16 posts — an estimate, because hole size and depth move the count.

Cost guidance

Costs on this page are ranges, labelled typical retail range — check the current shelf price before budgeting. No single national price is quoted, because decking, fencing, concrete and fastener prices vary by brand, product line, region and retailer, and a price that is right in one store can be wrong in the next. The way to budget is to multiply, not to guess: take the quantities from the worked example, multiply each by the shelf price of the exact product you have chosen, then add joists, screws, concrete, footings and delivery. The material moves the price most — composite costs more per square foot than pressure-treated wood, cedar sits between them and redwood costs more still, while vinyl fencing costs more per foot than wood fencing.

Two cost traps catch first-time buyers. The first is ordering the low end of the range and then paying a second delivery charge for the boards or pickets that finish the job. The second is forgetting the frame and the consumables: joists, screws, concrete and footings together are a meaningful share of a deck or fence job. Compare the total, not the per-board price, and keep spare boards or pickets from the same batch for future repairs. If you are hiring the work out, labour is usually quoted separately per square foot for decks or per linear foot for fences, and varies by region and by the ground conditions — a sloped site costs more than a flat one, so get the quote against the same measurements you used for the material count.

Step by step: measure, calculate, order

1. Measure twice. Measure the deck length and width, or the fence line, in feet, at the longest points, and note every gate, corner and change of direction. Ground is rarely flat — measure the slope, sketch the shape on paper, and convert inches to decimal feet (6 in = 0.5 ft) before multiplying.

2. Choose the material and the spacing. Pick the decking or fencing material first, then the joist spacing your product needs and the post spacing for your fence. The spacing decision belongs before the order, not after delivery, because it sets the joist, screw and post counts.

3. Use the calculator on this page. Enter the area or the length, the material and the spacing. The tool returns a range — plan on the high end. Check the product label against the calculator's assumed board width and spacing; if your boards are wider, the board count goes down but the area stays the same.

4. Order and check the delivery. Order the high end of the range, all from the same batch where it matters, and check the boards for warping and damage before building starts. Keep screws and concrete dry and within their shelf life.

5. Before you start building. Check the property line, local height rules and any permit needs, mark the post holes, and make sure you have spare boards, screws and concrete within reach. Finding you are a board short with the frame up is the most expensive kind of shortfall.

Common mistakes to avoid

The first mistake is measuring the deck or fence once and trusting it. Ground slopes, corners are rarely square and a fence line that looks straight can wander by a foot over its length — measure in sections and use the longest run. The second mistake is forgetting the waste allowance: boards are cut, ends are trimmed and a bad board is replaced, so the typical 5–10% extra is not padding, it is the job. The third mistake is buying the low end of every range at once — the low end of the board count, the low end of the screw count and the low end of the concrete count — which leaves no margin for a single bad cut. Buy the high end of the ranges that matter and keep the spares; a spare board from the same batch costs far less than a second trip. The fourth mistake is ignoring the ground: posts set too shallow or in too little concrete will lean, and footings above the frost line will heave, so dig to the depth your area needs and check local code before you pour.

Frequently asked questions

How many concrete bags do I need per fence post?

Typically 1–2 50 lb bags per post, or about half to one 80 lb bag per post. Deeper and wider holes need more — measure your hole size before you buy, and add the typical 10% extra for waste.

How many bags of concrete are in a cubic yard?

About 45 80 lb bags or about 60 60 lb bags per cubic yard. A cubic yard is 27 cubic feet, an 80 lb bag yields about 0.6 cubic feet and a 60 lb bag yields about 0.45 cubic feet.

How deep should a fence post hole be?

It depends on the fence height and the local frost depth — the hole should go below the frost line where frost heave is a risk. Check local code and your soil before you dig.

Can I set fence posts without concrete?

Some posts are set in compacted gravel, which drains better and is easier to replace later, but concrete holds better in soft soil and for tall fences. Follow the product instructions and local code.

What should I check before buying concrete?

Check the bag size and yield on the label, the hole size and depth, and the frost depth for your area. Buy a few extra bags — a post set in too little concrete will lean.

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