Fence Calculator

At 8 ft spacing, 100 ft is 12.5 bays, which rounds up to 13 sections and 14 posts on a straight run. At 6 ft spacing it is 17 sections and 18 posts. On a closed loop that returns to its starting post you drop one post, so 13 and 17.

The last bay will be short. Do not leave one 4 ft stub bay next to twelve 8 ft bays: pull the spacing in evenly across the whole run instead, so 13 bays of 7 ft 8 in rather than 12 of 8 ft plus a runt. It costs the same and it is the difference between a fence that looks built and one that looks calculated.

Take whichever of these three is deepest: one third of the height above ground, a 24 in minimum, or below your local frost line. For a 6 ft fence in a 36 in frost zone that is 36 in, because the frost line wins. For the same fence in a no-frost zone it is 24 in, because the one-third rule and the minimum agree.

Frost depth is a local code number, not a regional guess: it runs from zero in southern Florida and coastal California to 42 in or more in Minnesota, North Dakota and northern Maine. Call your building department. See fence post depth for the full breakdown.

Yes, and heavier. A gate hangs its whole weight off one post and adds a swinging, slamming load every time anyone uses it, which is exactly the load a line post never sees. Use 6x6 posts instead of 4x4, dig the hole 6 in deeper and 2 in wider in diameter, and set them in concrete even if you set the line posts in tamped gravel.

This calculator counts gate posts separately for exactly that reason and gives them their own concrete figure. For a gate wider than about 5 ft, or any gate carrying solid privacy boards, go to a 6x6 in a 12 in hole at minimum and consider a diagonal brace or a wheel at the latch end.

Sources genuinely disagree here and both work, so this is worth understanding rather than following. Concrete gives the most lateral resistance and is the standard for gate posts, corners, ends and any tall privacy fence. Compacted gravel drains freely, lets you reset a post later, and in wet clay soils often outlasts concrete because it does not create a bathtub that holds water against the wood.

The compromise most fence builders land on: gravel in the bottom 4 to 6 in of every hole for drainage, concrete above it, and the concrete crowned above grade so water runs away from the post rather than pooling at it. Never bury the concrete collar below grade in a dish shape.

Divide 12 by the picket width plus the gap, both in inches. A 5.5 in privacy board with no gap is 12 / 5.5 = 2.18 pickets per foot, so 219 pickets per 100 ft. A 5.5 in board with a 2.5 in gap is 12 / 8 = 1.5 per foot, so 150 per 100 ft.

The trap is nominal width. A "1x6" fence board is 5.5 in actual, not 6 in. Using 6 in leaves you about 8% short, which on a 100 ft fence is roughly 17 missing boards and one more trip to the yard.

For the most common hole, a 4x4 in a 10 in wide by 36 in deep hole, you need about 1.38 cu ft of concrete, which is 3 bags of 80 lb, 4 of 60 lb or 4 of 50 lb. A shallower 10 x 24 in hole takes 2 bags of 80 lb.

Two things change that number more than people expect. A wider hole costs far more concrete than a deeper one, because volume goes up with the square of the radius: going from 10 in to 12 in diameter adds 44% to the concrete at the same depth. And a 6x6 post displaces roughly two and a half times what a 4x4 does, which claws some of that back.

In this calculator, yes. Enter the full length of the fence line including the gate openings, then set the number of gates and their width. The gate widths are subtracted before sections are counted, because a gate opening does not need panels, pickets or rails, and then the gate posts are added back.

Measure the opening, not the gate. A 4 ft gate needs roughly 4 ft between the finished faces of its two posts, and the gate leaf itself is built about 1.5 in narrower to leave room for the hinges and the latch gap. If you buy a pre-built 4 ft gate, set the posts to the manufacturer's stated opening, not to 48 in.