Spirit level: common mistakes and how to avoid them

Learn to read a spirit level correctly and check it is accurate before you trust it.

SL-01Know the parts of the levelA spirit level is a straight bar with one or more sealed glass or plastic tubes called vials, each holding liquid and an air bubble. The long vial in the middle checks horizontal (level). Many levels also have a vial near one end for vertical (plumb), set at 90 degrees to the first. The bubble sits between two lines on the vial; when it is exactly between them, that direction is true.

SL-02Test your level for accuracy before trusting itCheap or dropped levels can be out of true, and beginners rarely think to check this. Rest the level on a flat surface, note where the bubble sits, then spin it 180 degrees end to end on the same spot. If the bubble reads the same both times, the level is accurate. If it shifts, the level is lying to you and should not be used for anything that matters.

SL-03Hold the level flat against the surface, not at an anglePress the full length of the level's edge against the surface you're checking, such as a shelf or a length of skirting. Don't let one end lift off or wobble. The most common beginner mistake is holding the level at a slight angle to see it better, which gives a false reading every time.

SL-04Read the bubble straight on, not from the sideGet your eye directly in front of the vial, level with it, not looking down or up at an angle. Looking from the side causes parallax error, where the bubble appears between the lines when it actually isn't. The bubble should sit dead centre between both lines, touching them equally, not just 'roughly close'.

SL-05Clear debris and dust from under the levelA tiny bit of grit, old filler, or dust under the level's edge will tilt the whole reading without you noticing. Wipe the surface and the level's underside with your hand or a cloth before every check. This matters most on old skirting, uneven timber, or masonry where debris collects easily.

SL-06Use a straight batten to level over long distancesA spirit level is usually 600mm to 1200mm long, but many jobs (like a run of shelving) are longer than that. Lay a straight, rigid batten of wood along the full run first, then put the spirit level on top of the batten to check it. Never 'walk' the level along a long surface in short hops and add up the readings in your head; small errors stack up fast.

SL-07Confirm your reading by flipping the levelOnce you think a surface is level, flip the level end to end (as in SL-02) on the exact same spot. If the bubble still reads level both ways, you can trust the result. If it changes, either the level is inaccurate or the surface genuinely isn't level, so recheck before you fix anything in place.

Save this as a project

Back to all guides