Fence Calculator

How to use the fence calculator

1. Choose Metric (m, cm, kg) or Imperial (ft, in, lb).
2. Under Fence sides, enter the Length (gates included) of each straight run and the number of Gates in this side. Use Add a side for each corner. Tick Closed loop (the fence goes all the way around) if the last side comes back to the first post.
3. Under Posts and rails, set the Post spacing (centre to centre), the Gate opening width and the number of Rails per section.
4. Under Boards or pickets, enter the Board width, the Gap between boards (0 for a privacy fence) and the Extra boards for waste (%).
5. Under Post holes and concrete, enter the Post width (square), the Hole diameter, the Hole depth and the Concrete bag size.
6. Read the posts, rails, boards, concrete and bags. The steps list every calculation; Reset defaults restores the example.

All calculations run in your browser.

How the quantities are calculated

• Fence length of a side = length − gates × gate opening width.
• Sections of a side = fence length ÷ post spacing, rounded up.
• Posts = all sections + one extra post per gate + 1 end post for an open fence. In a closed loop, the last section ends on the first post, so there is no extra end post. Corner posts are shared by two sides.
• Rails = sections × rails per section (one rail spans one section).
• Boards per side = (fence length + gap) ÷ (board width + gap), rounded up, then increased by the waste percentage.
• Concrete per hole = π × (hole diameter ÷ 2)² × depth − post width² × depth. Bags = concrete for all posts ÷ yield per bag, rounded up.

Metric example: one 15 m side with a 1 m gate leaves 14 m of fence. At 2.4 m spacing, that is 5.83, so 6 sections and 8 posts (6 + 1 for the gate + 1 end post), 18 rails and, with 14 cm boards and 1 cm gaps, 94 boards, or 99 with 5% extra. Holes of 25 cm × 1.2 m around 9 cm posts take 0.049 m³ each: 0.39 m³ in total, or 27 bags of 30 kg.

Imperial example: a closed 40 × 40 ft yard with one 4 ft gate and 8 ft spacing has 20 sections and 21 posts. With 5½ in boards and no gap, 343 boards. Holes of 10 in × 3 ft around 4×4 posts (3½ in) take 1.38 cu ft each, 29 cu ft in total: 49 bags of 80 lb.

Concrete bag yields

The bag presets are the same as in the concrete calculator, from the manufacturer’s data sheets for QUIKRETE Concrete Mix: 30 kg ≈ 14.7 L (0.52 cu ft), 40 lb ≈ 0.30 cu ft, 60 lb ≈ 0.45 cu ft and 80 lb ≈ 0.60 cu ft. Fast-setting post mixes yield less per bag: pick Other bag (enter its yield) and type the yield printed on the bag.

Planning tips

• 2.4 m (8 ft) spacing matches standard rail lengths; shorter spacing makes a stiffer fence.
• In cold climates, set posts below the frost line (often 1.2 m / 4 ft in Canada) to avoid heaving. Put 10–15 cm of gravel at the bottom of each hole for drainage.
• Gate posts carry more load: many builders use a larger post or a deeper hole there.
• Check the property line, the height limits and any permit required by your municipality, and have buried utilities located before digging.