How to Calibrate Your Level Like a Pro [with pictures]

Sep 12, 2019 | Custom Carpentry

Today we’re going to be discussing how to know if your level is properly calibrated or if for some reason it’s no longer calibrated the way it needs to be. It’s frustrating to build something using a level only to find out later in the project your level was slightly off. Here’s how the pros calibrate their levels.

Plumb vs. Level

What we’re going to discuss first is whether or not your level is plumb. Now, there are two different terms: plumb and level.

I know that if I hold my level up to a vertical structure, then we are discussing level. But if I hold it up against a horizontal structure, then I’m going to refer to that as plumb.

These are two separate terms, and they should be kept separate.

Calibrating Your Level for Plumb

So the first thing we’re going to do is check our level for plumb. We hold it up against a vertical structure. You can hold it up against any structure as long as it is relatively plum already. You know that if it sticks straight up and down it will probably work.

What we’re going to do is level with itself to see if it is calibrated correctly. I want to direct your attention to the lower of the two bubbles that measure plumb. You’ll see that my bubble is directly centered between the two lines, so it’s telling me that my 6X6 is in fact plumb. But we’re going to check it with the other bubble at the top of the level.

Look up there and see it is saying that the bubble is between the two lines. It’s saying that it’s plumb. What this is telling me is that these two bubbles are reading the same. They’re at least not different from each other. When you see that, it’s pretty safe to assume that it is plumb and it is calibrated accurately.

Verify Plumb

But we don’t want to guess. We want to know for sure. So in order to check that, what we’re going to do is invert the level. Swap it and put it back in the exact same location up against the same 6×6. We then check the bubbles again for plumb.

So if you put it right back there you will see that the bubble once again is directly between the two lines as it should be. And if you go to the top you will see that it is directly between the two lines as it should be there, as well. This tells me that this level is accurately reading plum, and is reliable.

Calibrating Your Level for Level

The next thing we will do is check the level against a horizontal structure to determine level. So I will lay it on top of my 2×6.

It’s important to know when checking a level against itself that you always should put it in the exact same location as you did the first time. Otherwise it may not read accurately.

So now that we have it down where we want it, we will check the level bubble on the left. I can see my bubble crowds the line on the right just a little bit. So let’s check the other bubble. I can see there that my  bubble on the right also crowds the line a little to the right just as the left bubble did.

What this tells me is that my horizontal 2×6 slants just a little bit down on the left. The 2×6 is off in this case, not my level. How do I know this? Because both of these are reading the same. So again, it’s safe to assume that they are both level.

Verify Level

But we don’t want to assume. Let’s make sure. What we’ll do is swap the level around again and put it back in the exact same location. Recheck the bubbles.

What I’m seeing here is that my bubble on the left (the one that was formerly on the right) is crowding the line to the right just a little bit just as it did before. And if you come over to the bubble that is now on the right, it actually appears to be centered.

It’s not crowding the line to the right. This tells me that this bubble needs to be adjusted just a little bit. So what I would do at this time is take out a pencil and put an X or some kind of mark on this level bubble that is off. This way I know next time I’m using this level that this particular bubble cannot be trusted.

How do we know that it’s this particular bubble? Simple. Because the bubble on the left always reads the same whenever you swap. But the bubble on the right reads differently whenever you swap it.

Consistency Is Key

So the key here in calibrating your level is consistency. If there is any form of inconsistency in the location of your bubble as it relates to the two lines on either side, that bubble is not trustworthy. You might go on build an entire structure, and it could all be wrong, because your level is out. So beware.

A level can be a builder’s or carpenter’s best friend or worst enemy. It all depends on if it’s properly calibrated or not.

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