A Laser Distance Meter sends a pulse of laser light to the target and measures the time it takes for the reflection to
return. For distances up to 30m, the accuracy is É3mm. On-board processing allows the device to add, subtract,
calculate areas and volumes and to triangulate. You can measure distances at a distance.
Compared with a good, old-fashioned tape there’s no contest. A Laser Distance Meter wins on every count: speed ,
accuracy, safety, versatility, convenience and functionality.
Ultrasonic devices offer many of the same features but are less accurate.
A Laser Distance Meter* sends out a finely focussed pulse of light to the target and detects the reflection. The meter
measures the time between those two events, and converts this to a distance. The formula is simple: Distance = Ä
(Speed x Time). However the speed of light is 300,000 km per second, so to resolve differences of (say) 1 cm, the meter
must measure time intervals of the order of billionths of a second. But don’t worry – the technology is well established
and reliable! A laser distance meter can measure distances of up to 30m with an accuracy of É3mm.
An Ultrasonic Distance Meter works on a similar principle, but instead of light it uses sound with a pitch too high for the
human ear to hear. The speed of sound is only about ⅓ of a km per second, so the time measurement is easier, but
there are other issues, as we shall see below.
* Note that we are not looking at laser ‘range finders’ – these are much less accurate, and are typically used in golf,
hunting and forestry.
Why not use a Tape?
A Laser Distance Meter is accurate to within a few millimetres, certainly equalling a tape for larger distances, and the
line is always dead straight – no bending or sagging! You have a choice of units, and there is no risk of misreading, as
with the intermediate marks on a tape.
The Laser Distance Meter is much faster – point, click, and you have the result in front of you on the display. The job is
done in just a fraction of the time it would take to use a tape.
You don’t need to walk to and fro, or have a helper at the other end. What is more, you can use it with one hand,
leaving the other free to hold your notebook.
With a backlit display and the laser dot itself, you can use your Laser Distance Meter in relatively poor lighting
conditions. There’s no need to wait until morning or to rig up lights.
You don’t have to access the far end of the measurement range or poke anything where it shouldn’t be poked. Only the
laser light has to do that – you do not have to worry about obstacles on the ground, or even large features such as pipes
or cables. If there is a line of sight to your target, and it is within range, you can very quickly find out exactly how far
away it is.
For the same reason, you can measure upwards without climbing – to a ceiling or to the top of a building. So, the Laser
Distance Meter brings safety benefits as well. No more scrambling up ladders or over steep or wet surfaces to get a
These safety and versatility benefits are particularly valuable in hazardous environments, and there will be occasions
when you would not be able to do the job at all with a tape. Only a Laser Distance Meter will do.
Suppose you have to measure up for a cable run
underneath a building? There is no line of sight between
the start and end of the run – you have to walk around the
corner. Obviously a complicated task with a tape, followed
by some work on a calculator. However with your Laser
Distance Meter you can measure two sides of a right-angled
triangle, and it will work out the third with its built-in
Similarly, you can get the height of a structure without even
being next to it, just by measuring your distance from the
base and from the top, and you can measure the width of a
building by standing some distance away and taking
measurements from there.
Something else that a tape simply cannot do is to work out an area from two length measurements, or a volume from
three measurements. Answers in seconds without a notebook and calculator.
Another feature intrinsic to a Laser Distance Meter is that it can measure continuously in situations where you would
have to reposition a tape repeatedly. You can walk along, marking out a path that is (say) a certain minimum distance
from a building. This is another bonus that has great value in hazardous environments.
A good old tape measure may be simple and reliable, but it is limited. You’ll need to find someone to hold the other end
and you’ll need to raise hot-work permits, make risk assessments and method statements. A Laser Distance Meter is
accurate and quick and requires only one person and one hand. It’s easy to use and versatile.
Laser Distance Meters have on-board processing enabling the device to triangulate and calculate – it knows Pythagoras!
You can measure distances at a distance, add, subtract and calculate areas and volumes. An Ultrasonic Meter has many
of the same features as a laser-based meter but is less accurate, less versatile, and less reliable. It is a lower range
product and a false economy!