Concrete Calculator for Fence Posts

Quick answer

Concrete Calculator for Fence Posts: size the hole about three times the post width, deep enough for frost and stability locally. Subtract gravel at the bottom and optionally the post displacement. A common 12 in × 2 ft hole with a 4×4 lands near three 80 lb bags.

Worked example with the concrete calculator for fence posts

Gross cylinder ≈ 1.57 ft³ for 12 in × 24 in. Post displacement ≈ 0.17 ft³. Concrete ≈ 1.40 ft³ → 3 bags after rounding. An 8 in hole of the same depth is often 1–2 bags.

Concrete Calculator for Fence Posts: Fence runs

Posts = length ÷ spacing + 1 for the end. Gate posts are often larger — count separately. Eighty feet at 8 ft centers is 11 posts; at 3 bags each you are looking at a pallet conversation.

Tubes vs dug holes

Full cardboard tubes that become the pier belong on the sonotube calculator. Dug holes with a wood post in the middle belong here.

Do it in Concrete Calculator

Open the post hole calculator, use fence layout mode for spacing, and round bags up.

Frost, gravel, and plumb

Local frost depth beats any national blog. Gravel under the post helps drainage on many fences; leave it out of the concrete depth. Brace the post plumb before and during the pour. Mix bags in batches you can place while the mix is still workable.

Gate posts and corners

Gate posts often use larger holes or tubes. Corners may get extra depth. Do not multiply a single typical hole by the post count if the plan shows upsizing at those locations — add a second pour for the heavy posts.

Field notes to keep handy

Measure to the outside of the forms. Convert every side to the same unit before you multiply. Apply waste after you sum every piece of the job, then round once for the plant.

Bag counts always round up because a partial bag is still a whole bag at the store. Compare that total with a delivered price when short-load fees show up on the quote.

Normal-weight planning density here is 150 pounds per cubic foot unless you switch it. Lightweight mixes and specialty bags can differ — read the ticket or the label when they do.

Field notes to keep handy

Measure to the outside of the forms. Convert every side to the same unit before you multiply. Apply waste after you sum every piece of the job, then round once for the plant.

Bag counts always round up because a partial bag is still a whole bag at the store. Compare that total with a delivered price when short-load fees show up on the quote.

Normal-weight planning density here is 150 pounds per cubic foot unless you switch it. Lightweight mixes and specialty bags can differ — read the ticket or the label when they do.