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

How to use a spirit level

Updated: 22 October 2026

The bubble sat between the lines, and the wall was still not straight. Learning how to use a spirit level is mostly about where you put your eye, which vial you trust, and whether that vial still agrees after you turn the tool around. This page is the method, not a shop. Listings and prices are on the [spirit level comparison](/hub/measuring-and-marking-tools/spirit-level). Peter F. used amazon.co.uk notes captured on 21 October 2026 and public methods from Johnson Level, BuildWiz and Stabila. There is no lab test. A qualifying amazon.co.uk purchase can earn a commission at no extra cost to you. If you do not own a level yet, length and body are in the [spirit level buying guide](/hub/measuring-and-marking-tools/spirit-level/sub/spirit-level-buying-guide).

The bubble sat between the lines, and the wall was still not straight.

Our top picks

STANLEY FATMAX Stanley FatMax 250 mm torpedo

Best overall

STANLEY FATMAX Stanley FatMax 250 mm torpedo
9.4/10about £14.99
View offer
Firecore Firecore 230 mm magnetic torpedo

Best value

Firecore Firecore 230 mm magnetic torpedo
9.2/10about £6.53
View offer
Franklin Sensors Franklin Sensors light level

Alternative

Franklin Sensors Franklin Sensors light level
9.2/10about £24.58
View offer
On this page
  1. 1.How to read level and plumb
  2. 2.The reverse test
  3. 3.When the wall is the problem
  4. 4.When to stop

How to read level and plumb

Clean the sole and the surface. A grit of plaster under one end is enough to throw a short level. Set the tool on the face you care about and put your eye in line with the vial. Reading from the side shifts the bubble in the curved tube, so you invent a slope. The centre vial, parallel to the sole, is level. The vial across the end is plumb when the sole is against a vertical face. Between the lines means that patch is inside the vial's band. It does not mean the whole wall is straight. A green light, such as the Franklin's, only says the short sole is close enough. It shows no number.

The reverse test

Prove the vial before you drill. On a flat worktop, pencil two marks just inside the ends of the sole. Note the bubble. Turn the level end for end in the same plane and set it back on those marks. Do not flip a horizontal vial upside down. The bubble should sit in the same place. BuildWiz treats the shift you see as about twice the real error. If the bubble has walked to the other side, stop. A digital pair should be equal and opposite when you swap ends. Plus 0.2° then minus 0.2° agrees. Plus 0.2° then plus 0.6° does not. The slope decision, when you need a number, is on digital spirit level vs bubble. Plumb has its own flip: the other end up, on the same marks. An end-for-end test on the flat does not prove the plumb vial.
STANLEY FATMAX Stanley FatMax 250 mm torpedo

Testsieger

STANLEY FATMAX Stanley FatMax 250 mm torpedo
9.4/10about £14.99
View offer

When the wall is the problem

A short level can pass every test and still leave you a crooked shelf. The bubble describes the sole, not the run. Slide it along in overlapping steps. If the bubble changes, the board is the variable. A door or a stud wants a sole near 1200 mm. This set's only listing of that length is the Grettz. If two positions on one shelf disagree, pack or plane to the high point rather than splitting the difference. Short magnetic levels in a tight gap are on the torpedo spirit level page.

When to stop

Stop when the reverse test fails, or when the job is no longer a shelf. New or altered foul drainage, a structural opening, gas pipe, and work inside a consumer unit belong to a competent person. A bubble does not display a 1:40 fall, and a 45° vial is not that fall. A level does not make an installation compliant. If the flip fails, return the tool.

Common questions

Where do I look when I read the bubble?
Put your eye in line with the vial, square to the marks, not off to one side. A sideways glance moves the bubble in the curved glass and invents a slope. Use the centre vial for level and the end vial for plumb. Between the lines means that face, under that sole, is inside the vial's band. It does not certify the rest of the wall.
How do I check a new level in the kitchen?
On a flat worktop, pencil two marks at the ends of the sole. Read the centre bubble, turn the level end for end on those marks, and read again. The bubble should match. Do not turn it upside down for this check. Then do a separate plumb check on a door jamb, with the other end up. If either bubble walks, do not fit the shelf with it.
What if the bubble moves when I reverse it?
The vial does not agree with itself. Stop, and do not average the two positions. One UK buyer of a Firecore 230 mm torpedo saw that shift and returned the tool. The same rule applies at any price. If the listing stated a tolerance, that description is part of what you paid for under the Consumer Rights Act 2015. Use another level while that one goes back.
How do I check plumb on a door jamb?
Hold the sole against the jamb and read the end vial with your eye square to it. Mark the contact, turn the level so the other end is uppermost, and read again. A level check along the head uses a different vial. A 230 mm tool can prove a short patch and still miss a bow. A full-height frame wants a much longer sole.
Why can a short level read level on a bowed shelf?
It only samples its own length. The middle of a sagging board can be locally level while the ends are low. Slide the level in overlapping steps. If the bubble changes, the board is moving, not the vial. A 400 mm sole bridges more of that hollow than a 230 mm one. Passing the reverse test does not stretch the sole.
When should I stop and get a professional?
Stop for new or altered foul drainage, a structural opening, gas pipework, and work inside a consumer unit. A spirit level cannot show England's 1:40 or 1:80 figures, and it does not make the work compliant in Wales, Scotland or Northern Ireland. Also stop if the reverse test fails and you have no second level. Fitting around a bad vial is how a crooked frame gets fixed in place.

Related pages

Best spirit level

Spirit level

Spirit level buying guide: length before the claim

Digital spirit level vs bubble: when you need a number

Torpedo spirit level: short gaps, not a door frame

Sources

Public sources from the digest, then the maker pages named there. Shelf prices are the amazon.co.uk figures stored for this set. Scores are the listing stars scaled for the table. This is not a laboratory test. Retrieved 22 October 2026.

  1. Approved Document H (England, 2015), Table 6 (retrieved 22 October 2026)
  2. Consumer Rights Act 2015, section 11 (retrieved 22 October 2026)
  3. Measuring Instruments (Material Measures of Length) Regulations 2006 (retrieved 22 October 2026)
  4. GOV.UK, laser radiation safety advice (retrieved 22 October 2026)
  5. Stabila, spirit level accuracy (retrieved 22 October 2026)
  6. Stanley UK, FatMax 0-43-609 (retrieved 22 October 2026)
  7. BuildWiz, spirit level (retrieved 22 October 2026)
  8. Johnson Level, reverse test (US method page) (retrieved 22 October 2026)