Fence Calculator

Your fence length in — exact panels, posts, and the concrete needed for every post hole, out.

✓ Free to use ✓ Standard panel width ✓ Post hole concrete built in ✓ Shareable results

Fence Length (m)

Panel Width (m) — standard UK panel is 1.83m (6ft)

▸ Post hole size

Hole Diameter (m)

Hole Depth (mm)

Panels Needed

Posts Needed

Actual Fence Length

Total Concrete Needed

25kg Bags (concrete mix)

✨ More for the job

Why your fence length rarely divides evenly

Standard UK fence panels come in 1.83m (6ft) widths. A 20m run divided by 1.83m gives 10.9 panels — since you can't buy a fraction of a panel, you round up to 11, which actually covers 20.13m, slightly more than your original measurement. This is completely normal and why fence runs are almost never buildable to an exact metre figure.

Posts always outnumber panels by one

Every panel needs a post on each side, and adjacent panels share a post — so a straight run of N panels needs N+1 posts, not N×2. An 11-panel fence needs 12 posts, not 22.

Worked example

A 20m fence with standard 1.83m panels needs 11 panels and 12 posts, covering an actual 20.13m. Each 300mm-diameter, 600mm-deep post hole needs about 0.042 m³ of concrete — across 12 posts that's 0.51 m³ total, roughly 43 bags of 25kg concrete mix.

Post hole depth should be roughly a third of the post's above-ground height, with a practical minimum around 450-600mm for standard garden fencing — deeper for taller fences or exposed sites. Check your specific panel/post system's manufacturer guidance.

Frequently Asked Questions

What if my fence has corners, not just a straight run?+

Calculate each straight section separately using this tool, then add the results together — corner posts are shared between two sections, so subtract one post per corner from your combined total to avoid double-counting. See why a 20m fence never comes out to exactly 20m →

Should I use post mix instead of standard concrete?+

Fast-setting post mix (like Postcrete) is convenient since it needs no mixing and sets in minutes, which is ideal for the small number of holes in a typical garden fence — see our Concrete Calculator for the bag comparison either way.

Do I need gravel boards too?+

Gravel boards (which sit below the panels, against the ground) typically match the same panel width and post spacing, so the same panel/post count from this calculator applies — just add the gravel board cost per panel separately.