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Fence Calculator

A fence is measured in length, not area. Enter the run to get post spacing, hole depth, concrete per hole, and the full material list.

  • Posts, rails, and pickets
  • Post depth and concrete per hole
  • Pool barrier rules

Project measurements

What kind of fence? This sets the material list

Pressure-treated privacy fence, the most common and the cheapest. Pickets, rails, and posts, all set in concrete.

The run Linear feet, not square feet

ft
ft
in
ft
in

Posts and footings The spacing and the setting

Setting the posts in

Does it enclose a pool? A pool fence is a barrier, not a fence

How this number is built

Fence math runs on linear feet. The spacing, depth, and concrete per hole appear in the result, not in a footnote.

Posts 8 feet apart, and a third of the post in the ground

Eight feet on center is the wood standard and what municipal chain-link specs ask for even though the material allows 10. The depth rule is that a third of the post's total length is buried. An 8 ft post for a 6 ft fence means 32 inches in the ground, not 24. Quikrete and Sakrete both add a 3–6 inch gravel base underneath, which drains the hole and is part of the depth budget rather than extra. In northern states the footing has to get below the frost line, commonly 36–48 inches, and local tables govern.

The hole is three times the post, and the concrete is less than you think

Sakrete's own guidance is a hole 3× the post's diameter, so a 4×4 wants a 10 to 12 inch hole. The part that is easy to get wrong is the volume: the post displaces 12–20% of the hole, so the concrete needed is the hole minus the post, not the hole. Quikrete's published example (two 50 lb bags for a 4 inch post in a 10 × 24 inch hole) is the snug end of the range; the arithmetic for an average hole gives 2.5, and a 6×6 post in the same hole takes materially fewer bags again. That is why a flat "two bags a post" estimate is wrong.

Terminal posts carry the load, and that is where fences fail

A line post holds up a rail. A corner, end, or gate post holds the whole run in tension, which is why chain-link specs call for 4 inch Schedule 40 terminal posts in 42–48 inch footings where the line posts are 2-3/8. A fence that leans in two years usually has an under-built terminal post or missing bracing: ASTM F567 requires truss-rod bracing for fences 6 ft and taller.

Concrete is not always the right answer

In heavy clay, or anywhere water stands, a concrete collar holds the water against the post. A post set in compacted gravel drains instead, and it can be replaced without breaking anything out. It is a standard method, not a shortcut, and this page will size the gravel for you.

If it encloses a pool, it is a barrier and not a fence

Pool barriers are prescriptive: 48 inches minimum measured on the outside face, no more than 2 inches of clearance under it, no gap that passes a 4 inch sphere anywhere, horizontal members between grade and 45 inches projecting no more than 1.75 inches (the classic privacy-fence violation), and gates that self-close and self-latch away from the pool with the release at least 54 inches up. A pool cover does not substitute for any of it. One caveat: local governments change pool codes often (California, Florida, Arizona, and Texas all differ from the base code), so treat the list above as typical requirements and confirm them with your building department before you build.

Check the height limit before you build eight feet of fence

Many jurisdictions cap fence height, commonly 6 ft at the rear and 3–4 ft in a front yard, and require a permit above that. This calculator will size an 8 ft privacy fence that your city may not allow, so the permit is worth a phone call before the materials are ordered rather than after.

Concrete for a post hole

Hole × depth Net cu ft 50 lb bags 80 lb bags
8 in × 24 in 0.53 2 1
8 in × 30 in 0.66 2 2
10 in × 24 in 0.92 3 2
10 in × 30 in 1.15 4 2
10 in × 36 in 1.38 4 3
12 in × 36 in 2.10 6 4

Net volume is π/4 × hole² × depth − post section × depth: the hole minus the post standing in it, which is the 12–20% that rule-of-thumb tables leave out and the reason they overstate the bags. These figures are for a 4×4 post; a 6×6 displaces far more and needs fewer bags in the same hole. Yield is 0.375 cu ft for a 50 lb fast-setting bag and 0.60 for an 80 lb mix. Quikrete's own worked example, two 50 lb bags for a 4 inch post in a 10 × 24 hole, is the snug-hole floor rather than the average, and this model returns 2.5 for the same hole.

Setting posts for a deck, a mailbox, or a sign instead? The concrete calculator has a generic post-hole shape for those, and the two do not double-count.

Where these numbers come from

  • Quikrete's Setting Posts guide and Fast-Setting Concrete Mix data sheet (the two-bag example for a 4 inch post in a 10 × 24 hole, the dry-pour method, water quantity, and staged filling), plus Sakrete's High-Strength Concrete Mix TDS for the 3× hole diameter, the one-third depth rule, and the gravel base. The displacement model is cross-checked against Quikrete's own example.
  • Eight feet on center for wood, from estimating guides; 10 ft maximum for chain-link line posts, from municipal and state specifications (KDH Water Systems, NY OGS, NY DOT, KDOT, Milwaukee, Gwinnett County), several of which tighten it to 8 ft. Terminal posts at 4 inch Schedule 40 with 42 to 48 inch footings, 21 ft top rail spliced with 6 to 7 inch sleeves, and ASTM F567 truss-rod bracing for fences 6 ft and taller come from the same specification set.
  • ISPSC 305, IRC 2018 R326, and IRC 2024 §AG105 for the 48 inch height, 2 inch bottom clearance, 4 inch sphere, 1.75 inch climbable-member limit, gate self-close, and self-latch rules, the 54 inch release, house-wall alarms, and the rule that a cover does not substitute. Read via municipal code summaries (Baton Rouge, Kennewick, Phoenix) rather than the standards themselves.
  • 2026 fence cost guides for installed per-linear-foot ranges, the material-only split, and gate costs. Secondary sources only: no trade-association price anchor was identified for fencing materials, so these are retail listings with no trade figure behind them.