Calculators / Fence calculator

Fence calculator

Turn a fence line into a shopping list: posts, rails, pickets and the concrete to set the posts.

US units (feet, inches, pounds); metric inputs accepted · Planning and purchasing estimate · Reviewed October 19, 2026

Start from a common job: 100 ft privacy fence, 1 gate 50 ft picket fence, 4 ft 150 ft backyard fence, 2 gates

Before you build: Call 811 before digging, and check permits, HOA rules and your property line. Posts in cold climates go below the frost line.

Supplier or contractor? Put this calculator on your own website with your logo, and get the customer’s quantities with each quote request. See how it works.

The formula

Sections = fence length ÷ post spacing, rounded up
Posts    = sections + 1, plus 1 for each gate
Rails    = sections × rails per section
Pickets  = fence length (in) ÷ (picket width + gap) × (1 + extra %)
Concrete = (hole area − post area) × (hole depth − gravel) × posts × 1.1
Post     = fence height + hole depth − gravel, rounded up to 8, 10 or 12 ft stock

Example: a 100 ft privacy fence, 6 ft high, with posts 8 ft apart and one gate has 13 sections and 15 posts. With 3 rails per section that is 39 rails, and 5½ inch pickets with no gap need 230 with 5% extra. Each 10 inch hole, 30 inches deep on 6 inches of gravel, takes 0.92 cubic feet of concrete, so the job needs 26 bags of 80 lb mix. The posts must be 8 ft long.

Quick answers for common fence lengths

6 ft privacy fence, posts 8 ft apart, one gate, 3 rails, 5½ in pickets with 5% extra, 10 in holes 30 in deep on 6 in of gravel.
Fence length	4×4 posts	2×4 rails	Pickets	80 lb bags
50 ft	9	21	115	16
100 ft	15	39	230	26
150 ft	21	57	344	36
200 ft	27	75	459	46

Before you dig

Call 811 (or file online) a few working days before digging. Utility companies mark buried lines for free, and in most states it is required.
Check your property line, permit rules and any HOA limits on height and style before buying materials.
Holes are usually about three times the post width and a third to half of the post’s height above ground deep, and below the frost line in cold climates. Your local building department can tell you the frost depth.

Sources and assumptions

Bag yields are the figures printed on standard premixed bags: 0.60 cubic feet for 80 lb concrete mix and 0.375 for 50 lb fast-setting mix. The concrete total adds 10% for uneven holes. Post sizes are actual: a 4 × 4 measures 3½ inches square.

Questions

How many posts do I need for a 100 ft fence?

15 posts at 8 ft spacing with one gate: 13 sections need 14 posts, and the gate adds one.

How many bags of concrete per fence post?

About 1.5 bags of 80 lb mix, or 2.5 bags of 50 lb fast-setting mix, for a 10 inch hole 30 inches deep around a 4×4 on 6 inches of gravel, before extra.

How deep should fence post holes be?

Usually a third to half of the post’s height above ground, and below the frost line where the ground freezes: about 24 to 36 inches for a 6 ft fence.

References and review

Units convert with exact definitions: 1 ft = 12 in = 0.3048 m, 1 yd³ = 27 ft³. Results round up to whole bags, sheets and pieces so you don’t come up short. Last reviewed October 19, 2026. If your bag, pallet or supplier lists a different figure, use theirs: change the matching field above.

Related calculators

Concrete calculatorCubic yards and 40, 60 or 80 lb bags for slabs, footings and post holes.Board foot calculatorBoard feet and cost of lumber from thickness, width and length.Gravel calculatorTons and cubic yards of gravel, crushed stone, sand or topsoil.