Fence calculator
Estimate panels, posts and concrete for a straight fence from total length, gate opening, panel width and post-hole dimensions.
Fence material estimate
Enter the fence length, gate opening and panel/post-hole data to estimate panels, posts and concrete.
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How does this tool work?
To fence a garden or a property boundary with welded mesh, timber or composite panels, the shopping list comes down to three items: panels, posts and the concrete that sets them. This calculator takes the total fence length, subtracts a gate opening, counts whole panels and posts, then estimates the concrete volume for the post holes and the number of bags from the yield printed on the bag.
The gate width is subtracted from the total length; the net length is divided by the panel width and rounded up: 19 m of 2 m panels needs 10 panels, the last one cut down.
On a continuous straight run you need one more post than panels. A gate opening splits the run in two and adds an end, so one extra post.
Each hole is treated as a cylinder: π × (diameter ÷ 2)² × depth. That volume is multiplied by the number of posts, increased by the concrete allowance, then divided by the yield of one bag in litres and rounded up to whole bags.
Limits: the fence line is assumed straight; for an L- or U-shaped run, calculate each side then remove one post per shared corner. The post volume is not deducted from the hole, which leaves a small reserve. The gate itself, its hinges, struts, base plates and fixings are not counted. Permitted height and planning rules depend on local regulations (in England, permitted development usually covers fences up to 2 m, 1 m next to a highway); post setting follows the manufacturer’s instructions, the soil and wind exposure.
Regular spacing gives a baseline number of bays and posts, but ends, corners, direction changes and gates can require additional posts or hardware. Match the calculation to the actual fence layout.
How to use this tool
Measure the fence line
Enter the total run in metres, opening included, measured with a string line between both ends.
Enter gate and panels
Enter the gate width, 0 if there is none, then the effective panel width between post centres.
Describe the holes
Enter the hole diameter and depth recommended by the instructions, for example 300 mm by 500 mm.
Convert into bags
Adjust the concrete allowance and the yield of one bag in litres, then read panels, posts, litres and bags.
Panels, posts and setting concrete
Each extra panel adds a post, and each post a hole to fill.
Panels
P = ⌈(L − gate) ÷ panel width⌉
g is the gate opening, w the panel width.
Posts
Np = P + 1 (+ 1 with a gate)
A gate creates one more run end.
Concrete
V = Np × π × r² × h × (1 + allowance)
r hole radius, h depth; bags = ⌈V ÷ yield⌉.
The volume assumes cylindrical holes filled with concrete, without deducting the post itself. Actual setting follows the fence system’s instructions.
Use cases
Back garden boundary
Count mesh panels and posts over 20 to 40 m of boundary with a pedestrian gate.
Street frontage with a driveway gate
Remove a 3 to 4 m gate from the fenced length and add the matching end post.
Planning the post concrete
Compare wide shallow holes with narrow deep ones in litres and bags before going to the builders’ merchant.
Examples
20 m fence with a pedestrian gate
19 ÷ 2 = 9.5, rounded up to 10 panels; 11 line posts plus one for the gate. Each hole holds π × 0.15² × 0.5 ≈ 35 L.
Input
20 m, 1 m gate, 2 m panels, 30 cm × 50 cm holes, 10% allowance, 12 L bagsResult
19 m of panels, 10 panels, 12 posts, 467 L of concrete, 39 bags35 m fence with a 3 m driveway gate
32 ÷ 2.5 = 12.8, so 13 panels. Narrower but deeper holes give about 29.5 L per post.
Input
35 m, 3 m gate, 2.5 m panels, 25 cm × 60 cm holes, 10% allowance, 10 L bagsResult
32 m of panels, 13 panels, 15 posts, 486 L of concrete, 49 bagsTips and best practices
- Measure panel width from post centre to post centre: a panel sold as 2.5 m often covers slightly more or less once fitted in its bracket system.
- A 25 kg bag of ready-mixed concrete often yields around 11 to 12 litres; use the yield printed on the bag you buy.
- On sloping ground, enter the length measured along the ground; panels are then stepped down the slope.
- For a heavy or swing gate, plan reinforced posts and footings, counted on top of the result.
Sources and references
Frequently asked questions
Why does the calculation add a post for a gate?
A break in the line of panels creates a new end. The exact position still depends on the gate system.
Can I use this calculation for rolled wire fencing?
The post logic is similar, but the panel calculation is not suited to measuring out a roll of wire mesh.
Is the concrete volume enough to design the footings?
No. It is a quantity estimate. Sizing the post footings depends on the soil, the loads and the fence system.
How many bags of concrete per post?
Work out the hole volume, π × radius² × depth, and divide by one bag’s yield. A 30 cm hole 50 cm deep holds about 35 litres, so 3 to 4 bags yielding 12 litres each.
How deep should post holes be?
It depends on fence height, wind load, soil and frost depth. The fence system maker gives the setting depth and diameter; dig deeper for a tall fence or a heavy gate.
How do I count a fence with corners?
The calculation covers one straight run. For an L or U layout, calculate each side separately, then remove one post for every corner shared by two sides.
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