Spirit Level Not Accurate? How to Check and Fix It

When You Can't Trust Your Level

Your spirit level is the foundation of accurate work. If it's lying to you, everything you build with it will be wrong. Here's how to check if your level is accurate and what to do if it isn't.

How to Check Level Accuracy

The flip test:

1. Place the level on a flat surface
2. Note the bubble position
3. Flip the level end-to-end (rotate 180°)
4. Place it in the same spot
5. The bubble should read exactly the same

If the bubble moves significantly, the level is out.

The reverse test (for plumb):

1. Hold level against a vertical surface
2. Note bubble position
3. Flip the level (still vertical, turn it around)
4. Bubble should read the same

Why Levels Go Out

Common causes:

• Dropped or knocked (most common)
• Stored improperly (bent)
• Temperature extremes affecting fluid
• Manufacturing defect
• Age and wear

Can You Fix an Inaccurate Level?

Adjustable vial levels:

Some professional levels have adjustable vials:

1. Use a known accurate reference (laser level or proven surface)
2. Adjust the vial mounting screws
3. Test and repeat until accurate
4. Check both level and plumb vials

Fixed vial levels:

Most levels can't be adjusted. If it's out, it's out. However:

• Minor inaccuracy might still be usable for rough work
• You can note the offset and compensate
• But for accurate work, replace it

When to Replace

Replace your level if:

• Fails the flip test
• Body is bent or damaged
• Vial is cracked or leaking
• Vial liquid is discoloured or has bubbles
• Edges are damaged (affecting surface contact)

A level is only useful if it's accurate. Don't keep using one you don't trust.

Choosing a Replacement

Quality indicators:

• Accuracy rating (look for 0.5mm/m or better)
• Rigid construction (box beam is strongest)
• Protected vials (won't break easily)
• Machined edges (better surface contact)
• Multiple vials for level and plumb

Sizes to consider:

• 600mm - good general purpose
• 1200mm - longer spans, more accurate over distance
• Torpedo level (230mm) - confined spaces, pipe work

Browse our hand tools collection for quality spirit levels.

Using Levels Properly

Even an accurate level can give wrong readings if used incorrectly:

• Clean surfaces: Debris under the level gives false readings
• Full contact: Level must sit flat along its entire length
• Read at eye level: Viewing at an angle distorts reading
• Wait for bubble to settle: Give it a second to stop moving
• Check both directions: Level isn't just one axis

Digital Levels

Digital/electronic levels offer advantages:

• Precise readout in degrees
• Audio signals when level is achieved
• Can be calibrated
• Often more durable than bubble vials

But they need batteries and are more expensive. For most trade work, a quality spirit level is sufficient.

Laser Levels

For critical work or frequent levelling:

• Project level lines across rooms
• Self-levelling saves time
• More accurate over long distances
• Can't be knocked out as easily

DeWalt and Makita both make excellent laser levels.

The Bottom Line

Test your levels regularly - especially after drops. If a level fails the flip test, don't keep using it for accurate work. Levels are fundamental tools; an inaccurate one undermines everything you do with it. Invest in quality, protect it from damage, and replace it when necessary.