How to mark a level line around the room accurately

Even if your spirit level is not very good.

Something I was taught very early on in my building career was that spirit levels “tell lies”…. Now that was probably just my old boss talking, after I’d pointed out something he built wasn’t level, but in a way he was right.

Spirit levels DO tell lies, about 0.15mm per M usually. Now that only adds up to 1.5mm in a 10m run which is not too much of a worry, but that’s when the level is brand new. After a few years kicking around on building sites and in the back of the van, not to mention being tapped a few thousand times by the brickies trowel, it might be a different story.

Then it could be 1mm out per M or more, and that could be a problem (or at least it should be, it never seemed to worry my old boss!). If you use a spirit level that’s inaccurate by 1mm out per M, to mark a line around a 4m x 4m room, your marks when they meet could be around 16mm out. Not good.

But not to worry, there is a way of using a battered inaccurate spirit level and still end up with a reasonably level line.

Simply turn it around each time you move and then any inaccuracies should cancel each other out as you move around the room.

Here, it’s easier to show you…

Simply turn the spirit level around each time you move it.

I hope that’s clear, let me know if it’s not!

Stay well

By Ian Anderson