Fence Calculator

Posts, rails, pickets, concrete, and cost per foot by fence type. Updated for 2026.

Last reviewed July 2026 · Free · Nothing you enter is stored

How this calculator works

Post count = length ÷ 8 ft spacing + 1, with two 50 lb bags of concrete per post. Wood privacy fences use 3 rails per section at 6 ft height (2 at 4 ft) and 2.18 pickets per linear foot for solid 5.5" pickets. Costs use 2026 national averages per linear foot installed — wood $32, vinyl $40, chain-link $25 — and DIY materials at roughly half that.

The waste allowance

This calculator adds about 10% to the picket count and rounds post and rail counts up to whole units. Pickets are where the buffer earns its keep: a fence line is never a perfect multiple of picket-plus-gap, so the last picket in each run gets ripped narrower, and a run that ends at a gate or a corner post usually takes two ripped pickets rather than one. On top of that, a pack of fence pickets always contains a few boards with a knot at the wrong place, a split end or a bow you would not want at eye level along a straight run. Concrete is the other place to be generous. Bags are cheap next to the labour of digging a hole, and a hole that ends up an inch wider than planned because the soil crumbled will swallow the difference without warning.

How deep the posts go

The working rule, and the one Quikrete publishes, is that the buried portion of the post should be one third to one half of the length standing above ground, plus another 6 inches at the bottom for a gravel drainage base. It is a rule of thumb rather than a code figure, but it is the one the trade runs on and it scales sensibly.

For a 6 foot privacy fence that means 2 to 3 feet of post in the ground, so the hole is dug 2 ft 6 in to 3 ft 6 in deep once the gravel is accounted for, and the post itself needs to be 8 to 9 feet long. For a 4 foot fence it means 16 to 24 inches of burial plus the gravel. Take the deeper end of the range for corner posts, gate posts and anything in soft or sandy soil, because those are the posts carrying lateral load rather than just standing there.

The 6 inches of gravel is not padding to save concrete. It gives the end grain of the post somewhere to drain to, which is the difference between a post that lasts and a post that rots from the bottom up while the fence above it still looks fine.

Concrete per post is a formula, not a chart

There is no manufacturer chart of concrete quantities for 4x4 and 6x6 posts at varying depths, and anyone presenting one has calculated it themselves. What Quikrete does publish is a single worked example: two 50 lb bags, each yielding 0.375 cubic feet for a total of 0.75 cubic feet, to set a 3 inch post in a 9 inch diameter hole 30 inches deep.

Everything else comes from geometry. The concrete volume is the volume of the hole minus the volume of the post inside it, and the bag count is that figure divided by the yield printed on the bag. The hole is a cylinder, so its volume is pi times the radius squared times the depth, and the post is a rectangular prism of its actual dimensions, which are 3.5 inches for a 4x4 and 5.5 inches for a 6x6 rather than the nominal numbers. Work in inches and divide by 1,728 to get cubic feet.

Two things move the answer more than people expect. Hole diameter is squared in that formula, so going from a 10 inch hole to a 12 inch hole is not a 20% increase in concrete but roughly 44%. And the gravel base occupies the bottom 6 inches, so the concrete depth is the hole depth less 6 inches. The table below works through the common combinations on exactly that basis.

Frost depth, and whether it applies to your fence

IRC section R403.1.4 sets footing depth at 12 inches minimum, or the local frost depth if that is deeper. That local figure ranges from effectively 0 inches in southern Florida to 60 inches or more in northern Minnesota and Maine, and your building department publishes it.

The honest caveat is that this provision governs footings for structural foundations. Whether it extends to fence posts varies by jurisdiction, and in many places fences are treated as accessory structures that are exempt from footing depth requirements altogether. Sites that state flatly that the IRC requires fence posts below the frost line are overreaching. Check your own municipality's fence permit rules before you commit to a hole depth, because the answer is local and it is easy to find.

What is not in dispute is the physics behind the rule. Water in the soil expands as it freezes and lifts whatever it can get purchase on, and a concrete cylinder with a rough surface is exactly that. A post that does not reach stable ground in a hard-freezing climate will heave a little each winter and settle imperfectly each spring, and after a few cycles the fence line is visibly uneven. Whether or not code requires it where you live, in a cold climate the deeper hole is the one that stays straight.

Spacing, rails and pickets

Posts are conventionally set at 6 or 8 foot intervals. Those numbers are trade convention tied to the rail and panel lengths sold at retail rather than a codified standard, which is worth knowing because it means the spacing is a choice. Eight feet suits standard 8 foot rails and full panels and keeps the post count down; six feet costs more posts but gives a stiffer fence, and it is the sensible choice for heavy panels or exposed windy sites.

Rail counts follow the same kind of convention. Two rails is normal for fences under about 4 feet, and three for privacy fences of 5 to 6 feet and up, where the extra rail keeps long pickets from cupping and twisting away from the line. Again, convention rather than code.

Pickets are pure arithmetic. Take the fence length in inches, divide by the picket width plus the gap width, and add about 10% as a buffer. A solid privacy fence uses a gap of zero, so the divisor is simply the picket width; a spaced picket fence with 5.5 inch pickets and a 2 inch gap divides by 7.5. The 10% covers ripped end pickets and the boards in every pack that are not straight enough to use.

Water is what actually kills a fence post

Almost every prematurely failed wooden fence post fails at the same place, which is the few inches immediately at and below ground level. Above that the post dries after rain; below it, sitting in a concrete cup with nowhere to drain, it stays wet. Pressure treatment slows that down, it does not stop it, and a cut end that was never re-treated is the fastest route in.

The gravel base at the bottom of the hole is the first defence. It gives water that runs down the post a path into the surrounding soil instead of pooling against the end grain. Setting a post directly onto the bottom of a concrete-filled hole builds a bucket, and a bucket is what you get.

The second defence is the shape of the concrete at the top. Quikrete specifies crowning it, sloping the surface away from the post on all sides so rain sheds off rather than sitting in the joint between wood and concrete. It takes a minute per post with a trowel while the mix is still workable, and it is skipped constantly. A flat or dished top holds a ring of water against the post after every rainfall, which is precisely the condition you spent the gravel avoiding.

Concrete per post by hole size and depth

No manufacturer publishes a chart like this, so these figures are calculated: the volume of the hole as a cylinder, less the volume of the post inside it, divided by the 0.375 cubic foot yield of a 50 lb bag. Concrete depth is the hole depth less the 6 inch gravel base. Post dimensions are actual, not nominal.

The first row is Quikrete's own published example — two 50 lb bags for a 3 inch post in a 9 inch hole 30 inches deep — and it computes to almost exactly two bags on this method, which is the check that the method is sound. The remaining rows are calculated the same way and rounded up to the next whole bag.

What goes wrong when setting fence posts

No gravel at the bottom of the hole. Setting the post straight onto concrete builds a sealed cup around the end grain. Water runs down the post, collects there and rots it from the bottom while the fence above still looks sound. Six inches of gravel gives it somewhere to drain.

Assuming the frost-depth rule applies to fences. IRC R403.1.4 governs footings for structural foundations. Fences are often accessory structures exempt from it, and whether the rule extends to posts varies by jurisdiction. Check the local fence permit rules rather than asserting a blanket requirement in either direction.

Leaving the concrete flat or dished at the top. Quikrete specifies crowning the concrete so it slopes away from the post on every side. A flat top holds a ring of standing water against the wood after every rainfall, which undoes the drainage the gravel was there to provide.

Buying concrete off a rule of thumb instead of the hole. Bag counts depend on hole diameter squared, so a 12 inch hole takes roughly 44% more concrete than a 10 inch one at the same depth. Two bags a post is a fair guess for a small hole and well short for a 6x6.

Treating 8 foot spacing as a rule. Six and eight feet are conventions tied to the rail and panel lengths sold at retail, not a standard. Heavy panels, tall privacy fences and exposed windy sites are better at six feet, and the extra posts cost less than a fence that leans.

Frequently asked questions

Why your state changes the price (but not the quantity)

How much fencing you need is physics — it doesn't care where you live. What it costs does. Labor rates, delivery distance, fuel, and local demand move installed prices by roughly 45 points from end to end: Arkansas, Mississippi, North Carolina sit near the bottom of the range, while Alaska, Hawaii, New York sit at the top. The Price this for selector at the top of the calculator applies a published construction cost index for your state to the 2026 national averages, so the dollar figures move and the material list stays put.

Treat the result as a budgeting range, not a quote. Two metros inside the same state can differ by more than the statewide index suggests, and a single busy contractor can outweigh both. See the full cost index for all 50 states and where the price data comes from.