Why a 20m Fence Never Comes Out to Exactly 20m

By Mr Need · Category: Home · Read Time: 4 mins · DIY

Fence panels don't bend to fit your exact measurement — your measurement gets rounded up to fit them. A 20m run and a 1.83m standard panel width don't divide evenly, and that mismatch is completely normal.

The rounding, worked through

Step	Calculation	Result
Raw division	20m ÷ 1.83m	10.9 panels
Rounded up	—	11 panels
Actual fence length	11 × 1.83m	20.13m

The fence ends up 13cm longer than the original 20m measurement — unavoidable once you're buying whole panels, and worth planning for at the boundary line rather than discovering on installation day.

Posts: +1, not ×2

It's a common assumption that more panels means proportionally more posts, but adjacent panels share a post — 11 panels need 12 posts, not 22. Getting this wrong on an order either leaves you short by nearly half, or paying for posts you'll never use.

🚧 Get your exact panel, post and concrete count

Enter your fence length for panels, posts and the concrete needed for every hole.

Use the Fence Calculator →

Frequently Asked Questions

What if my fence has a corner?+

Calculate each straight section separately, then subtract one post per corner from the combined total — corner posts are shared between the two adjoining sections.

Can I ask for a custom panel width to avoid the rounding?+

Some suppliers offer cut-to-size panels for a premium, but standard off-the-shelf panels are fixed-width, which is why the round-up is the normal, expected outcome for most DIY fence runs.