Fence Calculator
Enter the fence length, post spacing, rails per section, picket size and gates to get a full materials list: posts, rails, pickets and the bags of concrete needed to set the posts, in feet or metres.
Fence layout
Pickets
Post holes and concrete
Section preview
How to use the Fence Calculator
- Choose feet or metres at the top.
- Enter the total length, height and post spacing (8 ft or 2.4 m is common) and how many rails each section has.
- Add gates with their width; gate openings get no rails and an extra post each.
- Enter the picket width and gap (use a gap of 0 for a solid privacy fence) and a waste allowance.
- Set the post size, hole size and concrete bag, then press Calculate to see posts, rails, pickets and bags of concrete.
Fence calculation formulas
- Fenced length = total length − (number of gates × gate width).
- Sections = fenced length ÷ post spacing, rounded up.
- Posts = sections + 1 + number of gates.
- Rails = sections × rails per section.
- Pickets = length to cover ÷ (picket width + gap), rounded up.
- Concrete per post = π × (hole diameter ÷ 2)² × depth − post cross-section × depth.
Worked example: 100 ft picket fence with one gate
- Fenced length: 100 − 4 = 96 ft. Sections: 96 ÷ 8 = 12.
- Posts: 12 + 1 + 1 gate post = 14 posts. With 2 rails per section: 24 rails.
- Pickets (5.5 in wide, 0.5 in gap), gate covered too: 100 × 12 = 1,200 in ÷ 6 in = 200 pickets.
- Concrete: a 10 in × 24 in hole holds π × 5² × 24 = 1,885 in³, minus a 3.5 × 3.5 in post (294 in³) = 1,591 in³ = 0.92 ft³. For 14 posts that is 12.9 ft³, or 22 bags of 80 lb concrete at 0.6 ft³ each.
Concrete bag yields
| Bag size | Approximate yield | Bags per 4×4 post (10 × 24 in hole) |
|---|---|---|
| 40 lb | 0.30 ft³ | 3.1 |
| 50 lb | 0.375 ft³ | 2.5 |
| 60 lb | 0.45 ft³ | 2.0 |
| 80 lb | 0.60 ft³ | 1.5 |
| 25 kg | ≈ 11.7 L (0.0117 m³) | about 2.0 for a 100 mm post in a 25 × 60 cm hole |
Frequently asked questions
How many fence posts do I need?
Divide the fenced length (without gates) by the post spacing and round up to get the number of sections, then add one post for the end and one extra post per gate. A 100 ft fence with one 4 ft gate and 8 ft spacing: 96 ÷ 8 = 12 sections, so 12 + 1 + 1 = 14 posts.
How far apart should fence posts be?
6 to 8 feet (1.8 to 2.4 m) is standard for wood fences. 8 ft suits most picket and privacy fences built with 8 ft rails; use 6 ft for tall fences, windy sites or heavy boards. Chain link posts are usually up to 10 ft apart.
How many pickets do I need?
Divide the length to cover by the picket width plus the gap. For 96 ft of fence with 5.5 in pickets and 0.5 in gaps: 96 × 12 = 1,152 in ÷ 6 in = 192 pickets. For a privacy fence with no gap, use a gap of 0.
How many bags of concrete per fence post?
For a 4×4 post in a 10 in wide, 24 in deep hole, the concrete needed is about 0.92 ft³, so roughly 1.5 bags of 80 lb concrete (0.6 ft³ each) or 2.5 bags of 50 lb. The calculator multiplies this by the number of posts and rounds up.
How deep should fence post holes be?
A common rule is one third of the post's above-ground height, plus about 6 inches of gravel at the bottom for drainage: about 2 to 3 ft for a 6 ft fence. In cold climates go below the frost line. Holes should be about three times the post width.
How many rails does a fence need?
Fences up to about 4 ft high usually use 2 rails per section. 5 to 6 ft privacy fences use 3 rails to stop the boards warping, and 8 ft fences often use 4.
Do I need extra posts for corners?
This calculator assumes one continuous run. Every corner should have its own post, so if a corner does not fall on a regular post position, add one post per corner or enter each straight side separately and add the results.