How to Use a Stringline for Fencing (2026 Guide)
Aug 19, 2026
Getting a fence line straight starts with a stringline pulled taut between two fixed points, not with eyeballing posts as you go. This guide walks through setting out fence lines with a stringline in 2026, from corner pins to final post checks, the way UK tradespeople and confident DIYers actually do it on site.
- Set corner posts first, then run stringline taut corner to corner before placing any intermediate post — buy 8-braid line over twisted for this in 2026.
- Grettz 100m stringline in green, pink or yellow holds tension without stretching under normal fence-run loads. Buy it.
- A sagging line over 15-20m runs is the most common fencing fault — intermediate line pins fix it in seconds.
- Check post positions against the line, never against a second tape measure — the line is your reference, not your eye.
Why this matters
A fence that's out by 20mm at one end and dead straight at the other looks worse than a fence that's consistently off by 40mm across the whole run. The eye catches inconsistency, not absolute error.
A stringline gives you one continuous, tensioned reference from corner to corner. Every post you set gets measured against that same line, so any error stays uniform instead of compounding post by post. This is exactly why stringline for fencing and post alignment is the standard method on domestic and commercial fence runs in 2026 — it's fast, it needs no batteries, and it works in wind and rain when laser lines wash out.
What you'll need
- 100m stringline — 8-braid construction, not twisted. Twisted line stretches under tension and throws your measurements off over a 20-30m run.
- Line pins or wooden stakes — one per corner, plus intermediates on runs over 15m to stop sag.
- 50m steel tape measure — for post spacing and squaring off corners.
- A spirit level or laser level — to set post heights once the line confirms position.
- Corner posts already set — concrete-in or drive-in, these go in before the line goes up, not after.
Colour matters more than people think. Pink and yellow read clearly against grass and gravel in daylight; green disappears against a lawn but stands out against block paving or concrete. Pick the Grettz 100m stringline colour that contrasts with your ground, not the one that's already in the van.
The steps
1. Set your corner posts before anything else
Drive or concrete in the two end posts of the run first — everything else depends on these being right. Check them plumb with a spirit level and confirm the corner-to-corner distance with your tape measure before you touch the stringline.
Common mistake: setting intermediate posts by eye first and adjusting corners to fit them. Corners are the fixed reference. Fit everything to the corners, never the other way round.
2. Attach the line at a consistent height
Tie or clip the stringline to both corner posts at the same height above ground — 300mm up is standard for domestic fencing, high enough to clear grass and low mounds. Use a line pin or a nail so the line can be re-tensioned without re-tying knots every time.
Expected outcome: a level, taut line running the full length of the fence with no contact points along the ground.
3. Pull the line hand-tight, then check for sag
Tension the line as tight as you can pull it by hand — 8-braid line has enough tensile strength in 2026 stock to take a firm pull without snapping. On runs under 100m, one taut pull between two corner posts is usually enough.
On anything over 15-20m, sight down the line at eye level from one end. Any dip in the middle means you need an intermediate stake to lift the line back true before you start marking posts.
4. Mark post centres along the line
Measure along the taut line with your steel tape and mark each post centre at the panel spacing you're working to — 2.4m is standard for most panel fencing, though close-board and picket runs vary. Use spray marker or a peg pushed into the ground directly under the line at each mark, not next to it.
Common mistake: measuring along the ground instead of along the line. Ground measurement drifts on sloped or uneven plots; the line doesn't.
5. Set each intermediate post to the line, not to the last post
Drop each post so its face just kisses the stringline without pushing it out of true — you should be able to slide a piece of paper between post and line, not force the line sideways. Check this at both the top and bottom of the post face.
If you're setting posts to a datum height as well as a line position, cross-reference against a laser level for fencing and post lines — the stringline gives you the horizontal run, the laser gives you consistent post-top height across the whole fence.
6. Re-check tension after every third post
Line sags naturally as you work along a run, especially in warm weather when 8-braid line has slightly more give. Re-tension every three to four posts rather than waiting until the end — catching a 10mm sag early is a five-second fix; catching it after 15 posts means resetting several.
7. Final check before backfill or concrete
Sight down the full line one last time before you commit posts to concrete. Confirm no post has crept off-line during backfilling — post movement during compaction is the single most common cause of a fence line that looks straight from one end and crooked from the other.
Troubleshooting
- Line sags badly over 20m runs — add an intermediate stake at the midpoint and re-tension both halves separately rather than pulling harder on one end.
- Line is hard to see against the ground — switch colour. Pink and yellow outperform green on grass and soil; green reads better against paving and concrete.
- Knots slip under tension — use a line pin with a notch rather than tying directly to timber posts; friction knots on smooth stakes work loose after a day in the wind.
- Posts look straight but measurements don't add up — check the line hasn't been snagged on a weed, root, or low branch partway along the run. A 5mm snag reads as a straight line to the eye but throws every downstream measurement.
- Line frays or weakens after repeated use — 8-braid line resists this far better than twisted line; retire twisted stock after a season of regular site use.
- Corner posts are out of square — confirm the 3-4-5 triangle method on corners before running the line, not after — a line pulled between two out-of-square corners will always read as straight even when the fence isn't.
Tools and resources
- 100m 8-braid stringline in a colour that contrasts with your ground
- 50m steel tape for measuring panel spacing and corner distances
- A spirit level or laser level for post-top height, alongside the line for horizontal position
- Line pins or notched stakes for corners and intermediates
What to do next
Once the line's set and posts are marked, the next job is usually getting post-top heights dead level across the whole run rather than just square in plan — a rotary laser handles that faster than repeated spirit level checks post to post. If you're working brick or block alongside the fence line, the tensioning and colour-choice rules are slightly different — check the best stringline for bricklaying guide before you commit to line and pins for a mixed fence-and-wall job.
FAQ
What's the best stringline for fencing in 2026?
An 8-braid 100m stringline is the standard choice for fencing in 2026 because it resists stretch under tension better than twisted line. Colour should contrast with the ground — pink or yellow on grass, green on paving or concrete.
How do you use a stringline for fencing?
Set both corner posts first, then run the stringline taut between them at a consistent height, typically 300mm up. Mark intermediate post centres along the taut line at your panel spacing, then set each post so its face just touches the line.
Is a laser level better than a stringline for fencing?
A stringline handles horizontal run and post alignment better outdoors, especially in wind or bright sun where laser lines wash out. A laser level is better suited to checking post-top height consistency once the line has set the horizontal position.
How much does a stringline cost?
A 100m 8-braid builders stringline costs around £10-11 in 2026, with pink, yellow and green options priced the same. Twisted line costs less but stretches under tension and needs replacing more often.
How far apart should fence posts be?
Standard panel fencing uses 2.4m post spacing to match common panel widths sold in 2026. Close-board and picket fencing often use tighter spacing, so measure against your actual panel or board width before marking posts.
Why does my fence line sag in the middle?
Sag on runs over 15-20m happens because even 8-braid line has some give under its own tension over distance. Add an intermediate stake at the midpoint and re-tension each half separately rather than pulling harder from one end.
Can you use a stringline on sloped ground?
Yes, a stringline still gives an accurate horizontal reference on sloped plots because it measures along the line rather than along the ground. Set the line height at each corner post independently to account for the slope, then measure post centres along the taut line itself.
One last thing
Most fence lines that end up crooked weren't set out wrong — the line was fine, but nobody re-checked tension after backfilling. Compacting soil around a post shifts it by a few millimetres far more often than a bad initial measurement does, so the last sight-down-the-line check before concrete goes off matters more than the first one.
