First Layer Calibration: Bed Leveling, Z-Offset and Squish

Every print stands on its first layer, and a first layer is really just three variables: how level the bed is, how far the nozzle sits from it, and how much plastic comes out. This guide teaches you to read the layer with your own eyes, and to calibrate all three — whether your printer levels itself (Bambu) or hands you a sheet of paper (Ender-class).

What “correct squish” looks like

Print any flat, single-layer patch and look at the top surface of that first layer. There are only three things you can see, and each has a fix:

• Too far (not enough squish): each extrusion line stays a rounded strand, like spaghetti laid side by side. You can see the plate between lines, the surface feels corrugated, and lines peel off individually if you pick at a corner. The nozzle is too high — the plastic is being laid down, not pressed on.
• Just right: the lines flatten into ribbons that touch their neighbours with no gaps and no ridges — a continuous, slightly glossy sheet where you can still faintly see the line direction. Corners stay down, and the underside comes out smooth with a uniform texture from the plate.
• Too close (too much squish): the lines squeeze out sideways and pile into thin ridges where they overlap, so the surface feels rough in stripes and looks semi-transparent in places. Extreme cases add a dragging, clicking nozzle and a rippled, plowed look. This also produces elephant foot on the bottom edge.

Everything below is just machinery for moving your printer toward the middle description.

Bambu printers: the machine calibrates, you keep the inputs honest

Bambu machines probe the plate and level automatically before the print, and there is no user-facing z-offset knob to fiddle with. When a Bambu first layer goes wrong, the calibration was fed bad inputs. Your job list:

Manual printers: leveling and z-offset by hand

On an Ender-class machine with four bed knobs, you are the probe. The classic paper method, done in a way that actually holds:

1. Level hot. Heat the bed (and ideally the nozzle) to printing temperature first — beds change shape as they warm, so a cold-leveled bed is a lie.
2. Home, then disable steppers so you can slide the head by hand (or use the leveling assistant in the printer menu).
3. Do all four corners with a sheet of plain paper under the nozzle: adjust each knob until the paper drags with light, even friction — you should feel the nozzle touch, not pin, the paper.
4. Go around twice, then check the center. Each knob affects its neighbours, so one pass is never enough. If the corners are right but the center is high or low, the bed itself is bowed — a glass plate or a firmware mesh (many Ender variants support adding a probe) is the real cure.
5. Fine-tune the z-offset while the first layer prints. Use the firmware’s babystepping/Z-offset control and watch the lines: rounded strands → move the nozzle down in small steps; ridged, transparent stripes → move it up. Adjust in the smallest increments the menu offers, and save the offset when the layer matches the “just right” description above.

Re-check every few weeks: bed springs relax, and every violent print removal knocks a corner slightly off.

Flow: the third variable

If the bed is level and the height is right but lines still don’t fuse (or the surface over-fills into roughness everywhere, not just in stripes), the amount of plastic is off. Run your slicer’s flow-rate calibration once per filament brand — Bambu Studio and OrcaSlicer both have it built into the Calibration tab. Generic spools can be several percent off the profile’s flow ratio, and the first layer is where those percent show first. The under-extrusion and over-extrusion guides cover the symptoms in depth.

The rest of the first-layer checklist

Calibration is necessary, not sufficient. The two other first-layer killers are a greasy plate (wash it with dish soap and warm water — the ritual is in the build plate guide) and wrong temperatures for the material and plate combination. Symptom-by-symptom fixes live in the first layer problems guide, and sticking trouble specifically in the bed adhesion guide.

One habit ties it all together: watch the first layer go down before you walk away. Nearly every failure a print will ever have is visible in its first five minutes, and a ten-second babystep or a paused, re-washed plate is cheap compared to six hours of spaghetti on top of a bad foundation.

Shortcut: our calibration test print uses its whole 60×60 mm base plate as a first-layer test — print it and the AI reads squish and evenness straight from a photo.