How many fence posts do I need?
The post count is the run divided by your spacing, plus one for the closing post. Six to eight feet on center is the usual range. Go tighter for tall boards or a windy site.
Setting out the run before you dig
Call 811 before a shovel goes in the ground. The service is free, most states require two to three business days’ notice, and fence post holes are one of the most common places homeowners hit a buried gas, power or telecom line. In Canada 811 is the health line. File the locate at ClickBeforeYouDig.com or through your provincial one-call (Ontario One Call, Info-Excavation in Quebec, Utility Safety Partners in AB/SK/MB, BC 1 Call) and allow three to five business days. Ontario One Call is five by statute.
While you’re waiting on the locate, establish where your boundary really sits. Take it from a survey pin or a surveyor, not from the neighbor’s hedge. Moving a finished fence costs many times what a survey does.
Check the height rules at the same time. Six feet is the usual maximum in rear and side yards, three to four feet in a front yard or front setback. The model code exempts fences up to 7 ft from a building permit (IRC R105.2) and most jurisdictions follow it, so what usually binds is zoning rather than a permit.
Canadian bylaws are written in metric and run a little more generous. Toronto allows 2.0 m (6 ft 7 in) in rear and side yards, 2.5 m against a lane, and 1.2 m (4 ft) in a front yard.
Then measure the fence line rather than the property line, and measure on center. Drive a stake at every corner and every gate post, run a taut mason’s line between them, and take your run along that line, since that’s the number the calculator wants.
Don’t work post to post from one end, because the error compounds. A quarter inch of drift per section over thirteen sections is more than three inches of wander by the far corner, and you’ll see it from the house. Set the corner and gate posts in concrete first, let them cure, then space the intermediate posts against the string.
Deal with gates and the awkward last section on purpose. Subtract each gate opening from the run before you divide, and remember the opening isn’t the gate width.
Allow roughly three-quarters of an inch to an inch on the latch side, plus whatever the hinge hardware needs, plus an extra inch or two of ground clearance so the gate still swings once the posts have moved a season. Then spread any shortfall across the whole run instead of leaving a stub. Thirteen bays at 7 ft 8 in reads as deliberate. Twelve bays at 8 ft plus a 4 ft runt at the end doesn’t.
Post holes, concrete and the frost line
A post hole wants to be about three times the width of the post. Call it ten to twelve inches for a nominal 4x4 (which actually measures 3 1/2 inches). Depth is where the rule of thumb runs out. A third to a half of the above-ground height is the accepted range, so twenty-four inches is the shallow minimum for a six foot fence. Most installers want thirty-six under a privacy run.
In cold climates the frost line governs instead, and it varies enormously. Design frost depth is effectively zero in Florida, where codes still want twelve inches to reach stable bearing soil. It’s around forty-two inches in the Twin Cities and sixty to eighty inches in northern Minnesota and North Dakota. A footing that stops short of frost gets jacked a little every winter until the fence leans.
Concrete quantity follows the hole, not the post count. A 50 lb bag of fast-setting mix yields about 0.375 cubic feet (the Canadian equivalent is a 30 kg, or 66 lb, bag at about 0.50). Quikrete’s own chart puts two bags around a 4 inch post in a 10 inch hole two feet deep, and that’s where this calculator’s default comes from.
Scale up and the number climbs fast. A 12 inch hole thirty inches deep holds close to 1.75 cubic feet once you deduct the post, which is four to five bags. Work out your real hole volume before ordering and buy two or three bags spare. Dry-pour fast-setting mix straight into the hole with water on top, unless the ground is bone dry.
Do you have to use concrete at all? Not necessarily. Compacted angular gravel drains, and that matters because posts rot at the ground line, where a concrete collar holds water against the lumber. If you do use concrete, crown the top of the collar so it sheds rather than dishing it.
Two-part expanding polyurethane post mix is the third option. Manufacturers rate a single 33 oz pack as replacing two 50 lb bags of concrete, and it sets in minutes, though it’s sold for non-structural posts only.
Whatever you set them in, buy posts stamped for ground contact. Above-ground UC3B stock carries far less preservative and tends to fail years sooner in soil. Ground-contact stock is AWPA use category UC4A in the US and CSA O80 UC4A in Canada.
Cost, materials and when this calculator doesn’t fit
Budget in two parts, because the calculator prices pickets only. Picket choice swings a quote more than anything else. Wood fence materials as a whole commonly run $10 to $30 per linear foot (US pricing), with labor another $5 to $20 on top. Installed, a six foot wood privacy fence typically lands somewhere around $25 to $50 per linear foot, pressure-treated pine (SPF in Canada) at the lower end and cedar toward the upper. Cedar is a local species out West, though, so the gap between the two narrows there.
Vinyl runs roughly $40 to $85 installed, with a six foot privacy run usually landing at $40 to $60. It never needs staining, which usually makes it the cheaper option measured over twenty years. Add posts, rails, concrete, hardware and stain to the picket figure to get a realistic materials total.
The arithmetic here assumes a stick-built fence, where you choose the post spacing and cut pickets to suit. Pre-made panels invert that completely. A panel is a fixed six or eight feet wide, so the post spacing has to equal the panel width plus the post, exactly, and there’s no tidy way to narrow a panel that doesn’t fit.
With panels you set one bay at a time (dig the next hole, offer the panel up to locate the post, plumb, then concrete) rather than setting a whole line of posts and hoping. If your ground is uneven or you want the fence to follow contours, stick-built is the more forgiving choice.
Slopes need a decision before you buy lumber. You either step the fence, keeping each bay level and dropping it a fixed amount at every post (which leaves a triangular gap under each bay), or you rack it so the frame follows the grade. Racking is practical with stick-built fences and with panels sold as rackable, not with rigid ones. Stepping needs longer posts than the flat calculation implies, so add the total fall of the run to the uphill post length before ordering.
Neither approach changes the post count the calculator gives you, but both change the post lengths and the picket cuts.
How many fence posts for a 100 ft fence
Fourteen at 8 ft spacing, sixteen at 7 ft, or eighteen at 6 ft. Divide 100 by the spacing, round up to whole sections and add one for the closing post.
At 8 ft that’s 100 divided by 8, or 12.5, so thirteen sections and fourteen posts, with the leftover shared out evenly across every bay.
That count assumes one straight run with no corners. Every corner, end and change of direction is its own post and can’t be shared with the neighboring bay’s spacing. An L-shaped 100 ft fence with a single corner therefore takes fifteen rather than fourteen, and each gate adds a pair of its own.
Size them differently as well. Corner, end and gate posts carry the load, so they’re normally 4×6 or 6×6, set deeper and in more concrete than the line posts between them. The section count drives the rest of the order rather than the post count (thirteen bays at three rails each is thirty-nine rails).
How many bags of concrete per fence post
A 4×4 in a 10 in hole, 24 in deep, takes two 80 lb bags. Three 60 lb or four 40 lb bags do the same job. The hole holds about 0.92 cu ft once you deduct the post, and bags yield 0.60, 0.45 and 0.30 cu ft respectively, so the 60s and 40s land just over a whole-bag boundary and you round up.
Fill height explains the gap between that arithmetic and the charts. Quikrete puts two 50 lb bags of fast-setting mix on the same hole, which is 0.75 cu ft. It’s short of 0.92 until you remember their instruction to stop 3 to 4 in below grade and cap with soil, which brings the requirement down to about 0.79.
Note too that Quikrete sizes the hole at three times the post width, so 12 in for a 4×4 rather than 10. That takes the same 24 in hole to about 1.4 cu ft at full depth, or 1.2 stopping short of grade (three 80 lb bags rather than two).
Scale up honestly from there. A 12 in hole 30 in deep is 1.75 cu ft after the post, so four 60 lb bags. A 6×6 gate post in an 18 in hole 36 in deep needs about 4.7 cu ft — eight 80 lb bags for that one post. Buy two or three spares. Running short mid-pour costs more than the waste.
How far apart should fence posts be
Six to eight feet on center for wood. Eight is the practical ceiling, since that’s about as far as a 2×4 rail spans before it sags. Chain link goes to 10 ft, split rail to about 10 ft 4 in on standard 11 ft rails, and vinyl is locked to the panel width.
Match the spacing to the material rather than a single rule. Wood privacy at 6 ft costs more posts but stiffens a tall run and keeps rails from bowing in wind. 8 ft is fine at 4 to 6 ft tall on sheltered ground. Chain link’s 10 ft maximum comes from ASTM F567, the industry installation standard, and assumes a top rail or top tension wire carrying the fabric.
Vinyl and aluminum give you no choice at all. The post has to land at panel width plus post width, with no slack, and a panel can’t be neatly narrowed. Field and wire fencing runs 12 to 16 ft between line posts, with braced corner assemblies doing the real work. The 16 ft figure is the maximum in USDA NRCS and land-grant extension specifications for standard woven wire, and provincial agriculture extension gives the same number in Canada.
Common questions
How deep should fence posts be?
Go a third of the above-ground height, or below your frost line, whichever is deeper. For a 6 ft fence that’s usually 24–30 in across the South, 36–42 in through the northern states, and 42–72 in in Canada depending on the province. Add 6 in of gravel in the bottom so the post can drain.
How far apart should posts be?
Most wood fences run six to eight feet on center. Eight is the usual maximum for pre-made panels, and closer spacing stiffens a tall or exposed fence.
How much concrete per post?
Figure two 50 lb bags per 18 in of concrete in a 10 in hole around a 4×4. That’s the Quikrete post chart figure for a 24 in hole with 6 in of gravel under the post. Go below a frost line and it climbs (a 30 in hole takes three, a 48 in hole five). Dry-pour it and wet it in place unless the ground is very dry.
Do I need a permit to build a fence?
Usually not at standard heights, but rules are local. The model code (IRC R105.2) exempts fences up to 7 ft from a building permit, and most jurisdictions follow it. Toronto needs no permit at or under 2.0 m. Zoning still binds: typically six feet in rear and side yards, three to four in a front yard or setback, a variance above that. Check with your building or zoning department and any HOA, which often sets stricter height, style and color rules.
How many pickets do I need for a 100 foot fence?
With standard 5 1/2 inch pickets and half-inch gaps, each picket eats 6 inches of run, so 100 feet is 1,200 inches divided by 6, or 200 pickets. Butted tight with no gap the same run takes about 218. Gap width is the biggest driver by far, so settle it before ordering, and add a handful spare for splits and cull boards.
Should I set fence posts in concrete or gravel?
Concrete gives the most rigid post and it’s the right answer for corner, end and gate posts. Compacted angular gravel drains freely and lets a line post be reset later, which suits wet ground. Concrete’s weakness is that the collar holds water at the ground line, where posts rot. Crown the top so it sheds, and always use ground-contact rated lumber.
How do I space fence posts around a gate?
Treat the gate as a fixed opening and set its two posts first, then divide the remaining run. The post-to-post opening is the gate leaf plus roughly three-quarters of an inch to an inch on the latch side, plus the hinge allowance. Use a heavier post on the hinge side (4x6 or 6x6) and set it deeper than a line post, because a gate hangs its whole weight on it.
What length posts do I need for a 6 foot fence?
Add the burial depth to the finished height. A six foot fence set twenty-four inches deep (the shallow end of the one-third-to-one-half rule) needs eight foot posts, which is why 8 ft is the stock length. Go to the thirty-six inches most installers prefer, or let a deep frost line push the hole deeper, and you’ll want ten foot posts trimmed level once the concrete has set.
How many posts do I need for a 100 ft fence with a gate?
Count each side of the gate as its own run. A 4 ft gate leaves 96 ft of fence. Split as 50 ft and 46 ft, that’s eight posts and seven at 8 ft spacing, fifteen in total against fourteen for an ungated line. The two flanking the opening are the gate posts, so set those first, heavier and deeper, and space everything else off them.
Can fence posts be 10 feet apart?
On chain link, wire and ranch rail, yes. On a boarded wood fence, no. A 2×4 rail visibly sags past about 8 ft, and the boarded face acts as a sail in wind. Ten-foot bays in wood need 2×6 rails on edge or a mid-bay support, plus bigger posts to match, which usually costs more than the posts you saved.
How much concrete do I need for a whole 100 ft fence?
Figure twenty-eight 80 lb bags for fourteen line posts at two apiece, plus extra for the deeper corner and gate holes. Call it 34 to 36. Bagged concrete comes 42 to a pallet at 80 lb, and a full pallet usually prices better than three dozen loose bags. The leftovers are handy for a mailbox or clothesline post.