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.

What is the Z-Offset First Layer Calculator?

Converts a measured first-layer thickness from calipers on a test square into the exact Z offset adjustment in millimetres needed to hit your target layer height. Works for manual paper-test offsets and auto-levelling probe offsets. It runs free in your browser on Gera Tools, with nothing uploaded.

Z-Offset First Layer Calculator

Name: Z-Offset First Layer Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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.

Why the paper test isn’t precise enough

The paper test — sliding a sheet under the nozzle until there’s light drag — gets you close in maybe 2–3 minutes, but it has real limitations. The thickness of standard printer paper varies between brands (typically 0.08–0.12 mm), and the “right amount of drag” is a subjective feel that differs between operators. Two people calibrating the same printer with the same paper can produce offsets that differ by 0.05–0.10 mm.

For functional parts that need dimensional accuracy, or for materials like PETG that are sensitive to over-squish, a measured calibration is more repeatable and produces consistent results across sessions. The paper test is a useful starting point — use it to get within 0.2 mm or so, then use this calculator to zero in precisely.

Reading a first-layer test print

When you inspect the printed square (or a calibration pattern), look for these signs:

Appearance	Diagnosis	Adjustment
Gaps between lines, poor adhesion	Layer too thick (nozzle too high)	Move Z offset more negative
Lines fusing together smoothly	Good squish — target range	No change needed
Lines squashing flat, plastic spreading sideways	Layer too thin (nozzle too close)	Move Z offset less negative
Lines transparent / very flat, skipping	Nozzle dragging bed	Move Z offset significantly less negative

Measure in at least three positions — centre, and two opposing corners — since an unlevel bed means different actual gaps at different points. If the corners are consistently different from the centre, level the bed first, then re-measure.

Babystep adjustment in Marlin and Klipper

On printers running Marlin, you can adjust Z offset in real-time during a print using the Live Adjust Z or Babystep feature in the LCD menu or via M290 Z-0.04. In Klipper, SET_GCODE_OFFSET Z_ADJUST=-0.04 applies a live offset without stopping the print. Use these to confirm the new value while watching the first layer before saving it permanently with SAVE_CONFIG (Klipper) or M500 (Marlin).

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.