Z offset is the small vertical correction between where the printer thinks the nozzle touches the bed and where it actually does. A more negative offset pushes the nozzle closer to the bed, squishing the first layer thinner; a less negative offset lifts it for a thicker, looser first layer.

How is the offset adjustment calculated?

The adjustment equals target thickness minus measured thickness. If you sliced at 0.20 mm but measured 0.24 mm, the layer is too thick by 0.04 mm, so you lower the nozzle by moving the Z offset 0.04 mm more negative to squish it down to target.

Which way does the sign go?

If the measured layer is thicker than target, the nozzle is too high, so make the Z offset more negative by the difference. If the measured layer is thinner than target, the nozzle is too low, so make the offset less negative. The tool shows the signed value and the direction in words.

Why not just use the paper test?

The paper test gets you close but relies on feel, so the first layer can still be off by several hundredths of a millimetre. Measuring a printed square with calipers and applying this correction is far more repeatable and gets a glassy, even first layer.

Does a thicker first layer ever help adhesion?

A slightly squished first layer, a few hundredths under nominal, usually adheres best because it presses filament into the bed texture. Aim to land within about 0.02 mm of your sliced height; this tool tells you exactly how far you are off.

Z-Offset First Layer Calculator

A dialled-in first layer is the foundation of every good print, and it comes down to the Z offset — the tiny vertical correction that sets how hard the nozzle squishes the first layer into the bed. Instead of guessing with the paper test, print a square, measure it, and let this tool tell you exactly how much to move the offset.

How it works

The first layer’s thickness is governed by the gap between the nozzle and the bed at Z home, which is set by the Z offset. If the layer prints too thick, the nozzle is sitting too high and you need to bring it closer (a more negative offset). If it prints too thin, the nozzle is too low.

The correction is a direct subtraction:

Z offset adjustment = target thickness − measured thickness

Apply that signed value to your current offset:

new Z offset = current Z offset + (target − measured)

A negative adjustment means lower the nozzle (more negative offset); a positive adjustment means raise it.

Worked example

You sliced a single-layer square at a target of 0.20 mm. Calipers read 0.24 mm — too thick by 0.04 mm. The adjustment is:

adjustment = 0.20 − 0.24 = −0.04 mm

So move the Z offset 0.04 mm more negative. If your current offset was −1.50 mm, the new value is −1.54 mm. Re-print the square and it should now measure 0.20 mm.

Tips and notes

Measure the square in a few spots and average them, since bed levelling can vary across the plate. A first layer landing within about 0.02 mm of nominal is excellent, and a very slight squish (a few hundredths under target) often gives the best adhesion. On printers with live adjustment you can babystep Z by this amount mid-print to verify before saving. All calculations run locally in your browser.