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How to use a Bosch laser measure

Updated: 22 October 2026

You have just measured a bedroom for flooring and the Bosch reads about 12 cm longer than the steel tape, which is roughly the body of the tool. That gap is usually the reference edge, not a broken meter. Set the edge before you store a number, hold the tool still, and aim at a surface that sends the beam back. Model choice is on the [Bosch laser rangefinder comparison](/hub/measuring-equipment/bosch-laser-rangefinder). The steps follow Bosch Professional GB measuring instructions and a GLM manual, plus GOV.UK class 2 advice. We have not certified your instrument. A qualifying purchase can earn a commission at no extra cost to you.

You have just measured a bedroom for flooring and the Bosch reads about 12 cm longer than the steel tape, which is roughly the body of the tool. That gap is usually the reference edge, not a broken meter.

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Bosch Bosch Professional GLM 40-31

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Bosch Bosch Professional GLM 40-31
9.6/10about £90.28
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Bosch Bosch Professional GLM 40

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Bosch Bosch Professional GLM 40
9.2/10about £74.99
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Bosch Bosch EasyDistance 20

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Bosch Bosch EasyDistance 20
9.2/10about £43.99
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On this page
  1. 1.Set the edge before you trust the number
  2. 2.Take the shot
  3. 3.Check it, then decide if it is a fault
  4. 4.Where the tape still wins

Set the edge before you trust the number

Bosch manuals preset the rear edge when you switch a GLM on. The reading then runs from the back of the housing. If you meant the front, or the centre of a tripod thread, the number is long or short by that offset until you change the reference. Change it before you measure. Use Bosch: rear edge at switch-on. The EasyDistance does not offer that menu: it is one button and distance only. The GLM 40 title states a minimum of 0.15 m. Model choice stays on the Bosch laser measure buying guide.

Take the shot

Hold the tool still against a firm stop, except when you have switched to continuous mode and you are sweeping for a maximum or a minimum. Covering the lens or the outlet spoils the return. On a shiny worktop, tape a matt card to the surface, measure to the card, and peel it off. These meters are class 2. Do not stare into the outlet, and do not aim at a colleague on a ladder, where dazzle matters. GOV.UK does not call class 2 eye-safe.
Bosch Bosch Professional GLM 40-31

Testsieger

Bosch Bosch Professional GLM 40-31
9.6/10about £90.28
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Check it, then decide if it is a fault

Bosch's GLM manual describes a check on a known indoor length between 3 m and 10 m. Take ten shots in favourable conditions and compare them with the mean. The manual allows the deviation from that mean to stay within ±4 mm. That tolerance is Bosch's check, not a test we ran. If the spread stays outside that band after a clear lens and a matt target, stop using the number for a cut. A dead cell, or an error on every press, is a return. Do not cut a stair string to one angled shot.

Where the tape still wins

The tape still wins for cuts, for curves, and for gaps under about 100 mm. The GLM 40's stated 0.15 m minimum is one concrete version of that limit. The EasyDistance will not let you flip the reference the way a GLM menu does. If the laser and the tape disagree by the length of the housing, go back to the reference icon before you rip a board. Colour of the beam is a separate decision, on the Bosch green laser measure vs red page.

Common questions

Which edge is the Bosch measuring from?
On a GLM, Bosch presets the rear edge when you switch the tool on. The number runs from the back of the housing unless you select the front or the tripod thread before the shot. The EasyDistance has one button and no reference menu, so you cannot change an edge the way you can on a GLM. Check the icon every time you turn the tool on, and change it before you store the length.
Why is the reading long by the length of the tool?
The rear reference includes the body. If you wanted the front of the meter, or you compared a rear-edge laser shot with a tape hooked on the wall, the difference is about the length of the housing. Twelve centimetres on a bedroom is a typical version of that mistake. Set the front reference, where the model allows it, and measure again from the same stop.
How do you check a Bosch laser measure against a known distance?
Use a known indoor run of 3–10 m. Take ten shots in favourable conditions, with the same edge and a firm stop, and see whether they stay within ±4 mm of their mean. That band is from the Bosch GLM manual, not from a test by this site. A hallway you have taped once is enough. If the spread stays wide after a matt target and a clear lens, treat the tool as faulty.
Why does glass or a shiny worktop fail?
Glass, water, polished metal and a high-gloss worktop can send the beam off or return a false distance. Insulation, roughcast, a slanted face and layers of air at different temperatures do the same. Bosch asks for a light, matt target. Tape a piece of card to the glass or the splashback, measure to the card, and remove it. A jump of several centimetres on a surface that has not moved is a target problem.
When do you still use a tape?
Use a tape for cuts, curves and gaps under about 100 mm, and whenever you are marking a piece on the bench. The laser is the better solo tool for a room length. The GLM 40 listing starts at 0.15 m, so shorter gaps are already outside that title. Take the room with the laser, then mark the saw cut with the tape. If they disagree by the body of the tool, fix the reference before you cut.
When is a bad reading a fault rather than a technique?
Fix the edge, uncover the lens, and repeat the ten-shot check on a known 3–10 m indoor length. If the tool still scatters beyond ±4 mm of the mean, or it errors on every press, or a fresh cell does not restore it, that is a return. One wild shot after you moved your hand is technique. A boundary or a structural opening is a surveyor, not a second press of the button.

Related pages

Best Bosch laser measure

Bosch laser rangefinder

Bosch laser measure buying guide: range, then seal

Bosch green laser measure vs red for a bright room

Bosch laser measure outdoors: sun and the long shot

Sources

Public UK sources from the research digest, last checked on 20 October 2026. Shelf prices and star lines are the amazon.co.uk figures captured with these nine listings. The price bands are this set, not a market average.

  1. GOV.UK laser radiation safety advice (retrieved 20 October 2026)
  2. HSE AOR employer guidance (retrieved 20 October 2026)
  3. SI 2010/1140 Control of Artificial Optical Radiation at Work Regulations (retrieved 20 October 2026)
  4. Bosch Professional GB GLM 40-31 (retrieved 20 October 2026)
  5. Bosch Professional GB GLM 50-27 C (retrieved 20 October 2026)
  6. Bosch Professional GB GLM 150-27 C (retrieved 20 October 2026)
  7. Bosch DIY GB EasyDistance 20 (retrieved 20 October 2026)
  8. Bosch GLM application overview (retrieved 20 October 2026)