Fence Post Concrete Calculator
A 6 ft privacy fence sets 4×4 posts every 8 ft in 10″ × 30″ holes. Posts needed = fence length ÷ spacing + 1 per straight run, plus one extra at every corner and gate. Enter the count and the calculator gives bags per hole and the pallet total.
Buy 30 × 80 lb bags — under 1 yd³ bagged mix beats a short load.
- Net volume (16.1 ft³)
- 0.60 yd³
- Waste 10%
- + 0.06 yd³
- Ready-mix ticket
- 0.75 yd³
- Approx. weight
- 2,417 lb
- 80 lb bags
- 30
- 60 lb bags
- 40
- 40 lb bags
- 60
- Materials + delivery$6–$9 / bag · Sep 2026
- $180 – $270
- Installed (with labor)typ. $637
- $443 – $926
Quantities follow the ticket. Links may earn us a commission at no cost to you; they never change a number.
How to calculate post hole by hand
Per hole (ft³) = π × (Hole dia ÷ 24)² × Depth (ft) − (Post width ÷ 12)² × Depth (ft) · bags = ft³ ÷ 0.60
Worked example
- Hole: π × (10 in ÷ 24)² × 2.5 ft = 1.36 ft³.
- Post: (3.5 in ÷ 12)² × 2.5 ft = 0.21 ft³.
- Concrete per hole: 1.36 − 0.21 = 1.15 ft³ → 1.9 × 80 lb bags, call it 2.
- Eight posts: 9.2 ft³ + 10% = 10.1 ft³ → 17 × 80 lb bags (0.37 yd³).
- 4×4 post, 10″ × 30″ hole
- ≈ 2 × 80 lb bags
- 4×4 post, 12″ × 36″ hole
- ≈ 3 × 80 lb bags
- 6×6 post, 12″ × 36″ hole
- ≈ 2.5 × 80 lb bags
- 6×6 post, 18″ × 42″ hole
- ≈ 7 × 80 lb bags
Questions crews ask
How many bags of concrete for a 100 ft fence?
At 8 ft spacing that is 14 posts (13 bays + 1). Each 4×4 in a 10″ × 30″ hole takes about 1.15 ft³; 14 holes with 10% waste is 17.7 ft³ → 30 × 80 lb bags, or 36 × 60 lb bags. Buy a couple extra for the gate posts, which get deeper holes.
How many fence posts do I need?
Divide each straight run by the post spacing (6 or 8 ft) and add one. A 100 ft run at 8 ft is 12.5 → 13 bays, 14 posts. Corners and gates need their own posts; gate posts should be 6×6 in a deeper, wider hole.
Do fence posts need concrete at all?
For privacy fences and any post carrying wind load, yes. Light picket or wire fences on well-drained soil can be set in compacted gravel or crushed stone, which drains better and makes replacement easier. Gate posts always get concrete.