A figure per meter scales with the measurement; a flat figure does not. A laser stating ± 0.4 mm/m is 2 mm out over 5 m. A distance meter stating ± 2 mm is 2 mm out at any distance.
Why line lasers use per-meter figures
A leveling laser projects a line, and any angular error in that line becomes a larger height error the further you go from the tool. The error is fundamentally angular, so it is quoted per meter.
Why distance meters usually use flat figures
A laser distance meter measures time of flight. Its error comes mostly from the timing electronics, which does not care how far away the wall is — so the figure stays roughly constant.
Reading a mixed listing
Some meters state a per-meter figure, some a flat one, and some state one thing and mean another. Where a listing gives ± 3 mm (0.12 in)/m on a 20 m (66 ft) meter, read it as an error that reaches 60 mm (2.36 in) at full range, and check the manual.
What it means in practice
For a line laser at ± 0.4 mm (0.02 in)/m across a 5 m (16 ft) room, the stated error end to end is about 2 mm (0.08 in). Whether that matters depends entirely on what you are hanging, and it is the figure to compare against your own tolerance rather than against another laser.
This does not replace the manufacturer's instructions. Every accuracy figure, measurement category, laser class and detection depth on this page is reported from the manufacturer's own documentation and named as such — none of it is calculated here. Working near a live installation, and trusting a detector before drilling, are safety matters: follow the figures printed on your own instrument and in its manual, which take precedence over anything on this site, and where a job belongs to a qualified person, hand it to one.
What gets asked here
Which is better, flat or per-meter?
Neither — they describe different error mechanisms. What matters is whether the figure is published at all, and several instruments we compare publish nothing.
How do I compare a flat figure with a per-meter one?
Pick the distance you actually work at and convert. At 5 m (16 ft), ± 0.4 mm (0.02 in)/m is ± 2 mm (0.08 in), which is directly comparable with a flat ± 2 mm (0.08 in).
Last reviewed 31 August 2026