First Layer Squish Calculator
Calculate actual first layer height and line spread from z-offset baby steps and squish percentage.
Improve bed adhesion with the right squish target.
The first layer is the foundation of every print, and the z-offset sets everything. Too high and the filament does not stick. Too low and you risk nozzle crashes or so much squish that the layer cannot be removed cleanly.
What squish actually means
When you lower the nozzle closer to the bed (negative z baby-step in most firmware), the first layer is physically compressed thinner than the nominal layer height. The plastic has to go somewhere, so it spreads wider. By conservation of cross-sectional area:
actual_width = nominal_width x (nominal_height / actual_height)
where actual_height = nominal_layer_h + z_baby_step (negative baby-step = nozzle lower = thinner layer).
Squish percentage
squish_pct = (nominal_height - actual_height) / nominal_height x 100
The sweet spot for most printers is 15-30% squish on the first layer. Under 10% and the layer barely bonds to the bed. Over 40% and you risk embedding the nozzle or over-squishing to the point where lines merge and create z-scar artifacts on the bottom face.
Practical example. Nominal first layer height 0.20mm, z baby-step -0.05mm: actual_height = 0.20 + (-0.05) = 0.15mm squish = (0.20 - 0.15) / 0.20 x 100 = 25% actual_width = 0.48 x (0.20 / 0.15) = 0.64mm (assuming 0.48mm nominal line width)
The line spreads about 33% wider. For a smooth bottom surface this is usually desirable. For dimensional accuracy on the first layer it is worth knowing.