Fence Calculator
Posts, rails, pickets and bags of concrete for any fence length, with your post spacing and hole size.
Step 1 · Fence layout
Measure the total run, leaving out gate openings.
Units
ftm
ftm
cornerscorners
Step 2 · Pickets
Pickets are counted across the full fence length.
incm
incm
Step 3 · Posts & concrete
Concrete fills each hole above the gravel, around the post.
incm
incm
incm
Straight runs assumed. Add one corner for each change of direction; gates are not included.
- Posts
- 14
- 4×4 · 13 sections
- Rails
- 39
- 3 per section · 8 ft long
- Pickets
- 219
- 5.5 in wide · 0 in gap
- Concrete bags
- 22
- 80 lb · 12.9 ft³
100 ft ÷ 8 ft = 13 sections → 14 posts · 0.9 ft³ concrete per post ÷ 0.60 ft³ per bag = 22 bags
Results link:
Rails: 2 per section for fences up to 4 ft tall, 3 up to 6 ft, 4 for taller fences.
Materials list
100 ft fence · posts every 8 ft · 3 railsQuantities rounded up to whole pieces and bags. Gates, post caps, brackets and fasteners are not included.
Open or edit this calculation:
How the quantities are calculated
The fence is split into sections at your post spacing. Every section needs its rails; posts are one more than the sections, plus one for each corner. Concrete is the volume of each hole above the gravel base, minus the post itself.
sections = ⌈length ÷ post spacing⌉
posts = sections + 1 + corners
rails = sections × rails per section
pickets = ⌈length ÷ (picket width + gap)⌉
concrete per post = (π × (Ø ÷ 2)² − post²) × (depth − gravel)
bags = ⌈posts × concrete per post ÷ bag yield⌉
posts = sections + 1 + corners
rails = sections × rails per section
pickets = ⌈length ÷ (picket width + gap)⌉
concrete per post = (π × (Ø ÷ 2)² − post²) × (depth − gravel)
bags = ⌈posts × concrete per post ÷ bag yield⌉
Assumptions
| Item | Assumption |
|---|---|
| Layout | Straight runs. Each corner adds one post. |
| Post size | Actual widths: 4×4 = 3½″, 6×6 = 5½″. |
| Concrete yield | 0.0075 ft³ per lb of dry mix (0.60 ft³ per 80 lb, 0.45 per 60 lb, 0.375 per 50 lb). Metric bags use the same ratio. |
| Rails | One rail spans one section, so rail length = post spacing. |
| Not included | Gates, post caps, brackets, nails or screws, stain. |
Worked example
A 100 ft straight privacy fence with posts every 8 ft, 3 rails, 5½″ pickets, 10″ × 30″ holes with 6″ of gravel and 80 lb bags:
sections = ⌈100 ÷ 8⌉ = 13 · posts = 14 · rails = 39
pickets = ⌈1,200″ ÷ 5.5″⌉ = 219
concrete per post = (π × 5² − 3.5²) × 24 ÷ 1,728 = 0.92 ft³
bags = ⌈14 × 0.92 ÷ 0.60⌉ = 22
pickets = ⌈1,200″ ÷ 5.5″⌉ = 219
concrete per post = (π × 5² − 3.5²) × 24 ÷ 1,728 = 0.92 ft³
bags = ⌈14 × 0.92 ÷ 0.60⌉ = 22
Frequently asked questions
How far apart should fence posts be?
Most wood privacy and picket fences use posts 6 to 8 ft apart, measured center to center. 8 ft spacing matches common 8 ft rail stock; closer spacing makes a stiffer fence, which helps in windy areas or with heavy panels.
How deep should fence post holes be?
A common rule of thumb is to bury about one-third of the post’s total length, and at least 24 inches. In cold climates the hole usually needs to go below the frost line. Check your local building code or permit office before digging.
How many bags of concrete do I need per post?
It depends on the hole. A 10″ hole with 24″ of concrete around a 4×4 post needs about 0.92 ft³, roughly 1.5 bags of 80 lb mix (each yields about 0.60 ft³). The calculator works this out for your hole size, gravel base and bag size.
How many pickets are in an 8 ft section?
Divide the section length by the picket width plus the gap. With 5½″ pickets and no gap, 96″ ÷ 5.5″ = 17.5, so you need 18 pickets per 8 ft section.
Does the calculator include gates?
No. Gates need their own posts, hinges and latch hardware. Leave the gate openings out of the fence length and add each gate separately.
Sources
- Concrete mix manufacturers’ published bag yields (yield is printed on each bag).
- Your local building code and permit office for post depth, frost line and fence height limits.
Testing
Formulas are shown on this page, based on the cited sources, and covered by automated tests. Methodology