Independent comparisons. We may earn from shop links. More info

String line level vs laser level

Updated: October 2026

You are setting out a patio, a fence, or a drain, and a centred bubble feels like a datum. A string line level vs laser level choice is three jobs. The string is the straight line you lay to. A hanging vial can level a short run. A laser or an optical level is what you hire for a height around a building, or a fall in millimetres. The ten vials in the [string spirit level comparison](/hub/measuring-and-marking-tools/string-spirit-level) state no millimetres per metre. How to hang one vial is on [how to use a string spirit level](/hub/measuring-and-marking-tools/string-spirit-level/sub/string-spirit-level-how-to-use). Methods were compared on 16 October 2026. A purchase through our links can earn a commission at no extra cost to you.

You are setting out a patio, a fence, or a drain, and a centred bubble feels like a datum. A string line level vs laser level choice is three jobs. The string is the straight line you lay to.

Our top picks

Presch Presch 2-piece line spirit level

Best overall

Presch Presch 2-piece line spirit level
8.1/10about £11.99
View offer
Bubble Levels Bubble Levels 7-piece hanging line level

Preis-Tipp

Bubble Levels Bubble Levels 7-piece hanging line level
7.3/10about £5.99
View offer
Vnuipofa Vnuipofa 2-piece aluminium line level

Alternative

Vnuipofa Vnuipofa 2-piece aluminium line level
4.3/10about £6.96
View offer
On this page
  1. 1.Three jobs, three tools
  2. 2.Where the string still wins
  3. 3.A fall is not a centred bubble
  4. 4.What an optical level is claiming
  5. 5.Hire when the far end would show

Three jobs, three tools

The first job is a straight course or a straight row of posts. A taut builders' line does that. The bricklayer's version runs between leads, on the string spirit level for bricklaying page. The second job is a rough level between two stakes. A hanging vial is for that, once the line is tight and one level is in the middle. The third job is a datum: the same height at the patio, the far post and the house wall. Arbtalk uses the string for the line and a laser for heights. Grettz puts it as laser for the datum, string for the post line, tape for the spacing. ShunTool keeps a line level for rough setting-out and moves to a laser or an optical level when 15 mm at the far end would matter. That 15 mm was not measured on these packs.

Where the string still wins

Use the string when you can see both ends and the work is the line itself. A short garden fence, on ground you will accept as roughly level, can stay on a cord and one checked vial. Mark the ends, space the posts with a tape, and plumb each post on its own. The string spirit level buying guide is the buying order if you still need a pack. The string loses when the ends are out of sight, when sag becomes the height, or when one level has to hold on more than one line. Wind, thin nylon and a heavy pack all dip the middle, and the bubble reports the dip. A rotary laser or an optical level throws a plane you can walk around.
Presch Presch 2-piece line spirit level

Testsieger

Presch Presch 2-piece line spirit level
8.1/10about £11.99
View offer

A fall is not a centred bubble

A centred bubble is zero fall. Approved Document H, Table 6, read here from the Welsh-hosted PDF, sets foul-drain gradients by pipe size and flow. 1:40 is 25 mm per metre. 1:80 is 12.5 mm per metre. You cannot get either by parking the bubble between the marks. A short pipe can be set with a straight-edge and a packer, which is what a supplier such as Kalsi shows. The packer is a known thickness under one end. Do not treat one supplier fall as Table 6. A rotary laser that can be tilted is a different instrument from a vial that only centres. Drainage that Building Regulations cover, including a sewer connection, is a job for someone competent to check it.

What an optical level is claiming

A CIRIA setting-out extract quotes a builder's optical level at plus or minus 5 mm over 30-50 m. That figure belongs to a tripod and a staff. They do not belong to a plastic vial with no printed tolerance. None of the ten listings states millimetres per metre. Stanley's 0-42-287, not in this set, states 2 mm/m and calls the precision secondary. Do not match these packs to the CIRIA sentence.

Hire when the far end would show

Hire the optical level or a rotary laser for a datum around a building, a long fence on a slope, or a fall you must record. Keep the string for a straight course or a short post run you can see. The top pick and the best value on the main page compare review files. If 15 mm at the far end would matter, you have already left the string.

Common questions

Is a string level accurate enough for a patio?
For a straight edge you can see, and a rough level between two stakes, yes, if the line is taut and a second vial agrees. It is not a datum for a whole patio on a slope, and it is not a fall. None of these listings states millimetres per metre, so this means good enough to mark two ends, not a tolerance.
When do I hire a laser or an optical level?
When you need a height that holds over a long run, around a corner, or on a slope. Arbtalk fencing posts use the string for the line and a laser for the heights. ShunTool's picture is 15 mm at the far end. A builder's optical level, in the CIRIA extract, is talked about in millimetres over 30-50 m. A Saturday line between two garden stakes is not that hire.
What does Table 6 actually say?
Under 1 litre per second, 75 mm and 100 mm foul drains fall at 1:40. Above that flow, 75 mm is at 1:80, 100 mm is at 1:80 with at least one WC, and 150 mm is at 1:150 with at least five WCs. That is Table 6, not one fall for every pipe. A centred string level matches none of those rows.
Should fence posts be straight with string and level with a laser?
On a long run or a slope, UK fencers use string for the straight line, a laser for the heights and a tape for the spacing. On a short, roughly level run you can keep the heights on one taut cord, if you plumb each post separately. The string does not plumb the post.
Who signs off a drain?
Someone competent to design and check drainage that Building Regulations cover, including a sewer connection. Table 6 is the gradient guidance. It does not make a hanging vial into that check. For a short patio fall you can measure a drop yourself. For a foul drain, the sign-off is not a bubble on a piece of nylon.

Related pages

A centred bubble is not a drain fall

String spirit level

Best string line level UK: match the listing to the job

String line level buying guide: job before the pack

Builders line bricklaying: the line is the straight-edge

How to use a string line level: taut line, one vial

Sources

Public UK sources and the amazon.co.uk listings in the research digest, checked on 16 October 2026. Shelf prices can change.

  1. Approved Document H: drainage and waste disposal (retrieved 16 October 2026)
  2. Consumer Rights Act 2015, section 22 (retrieved 16 October 2026)
  3. Stanley 80 mm line level 0-42-287 (retrieved 16 October 2026)
  4. BS 958:1968, precision spirit levels (retrieved 16 October 2026)
  5. BuildWiz: builders' line (retrieved 16 October 2026)
  6. HSE: slips and trips in construction (retrieved 16 October 2026)
  7. Johnson Level: line levels (retrieved 16 October 2026)
  8. amazon.co.uk: string line level (retrieved 16 October 2026)