Bed Leveling, First Layer Thickness, and Z-Offset
In 3D printing, three topics cause more confusion—and more failed prints—than any others: bed leveling, first layer thickness, and Z-offset. These are the absolute foundation of the 3D printing process. If you get them wrong, no amount of glue stick or hairspray will save your print.
We frequently see users mixing these terms up, leading to frustration. In this guide, we are going to dismantle the common misconceptions and look at the reality of how your machine finds "zero."
- Tools: Digital Calipers and Flashlight
- Recommended reading: The Perfect First Layer
- Ensure your nozzle is clean and free of plastic debris
The Difference Between Leveling and Zeroing
Most beginners start with the "Four Corner Paper Method." While effective, it is critical to understand that this process actually performs two distinct functions simultaneously:
- Leveling (Tramming): ensuring the build plate is parallel to the nozzle’s movement.
- Zeroing (Z-Offset): telling the printer where the build surface actually begins.
Most users understand the concept of leveling (making it flat). The confusion usually lies in Zeroing.
When you level your bed, you are answering a specific question for your printer: "Where is the top of the build surface?" Your first layer height is calculated from this point. If your answer to the printer is wrong, your first layer will be wrong.
The "Paper Method" Trap
A question we see on forums nearly every day is: "What is the ideal distance between the nozzle and the bed when leveling?" or "I own feeler gauges; which thickness should I use?"
The technical answer is 0.00mm.
The goal is for the nozzle to be exactly at the height of the bed (Z=0). Of course, there is no such thing as a 0mm feeler gauge. This is why we advise using the thinnest material you have available.
Here is the math behind why standard paper often fails:
If you level your bed using a standard sheet of copy paper (typically 0.1mm thick), you have mechanically set your "Zero" at 0.1mm above the bed. If you then slice your file with a First Layer Height of 0.2mm, your printer will move to what it thinks is 0.2mm.
However, because of that initial paper gap, the nozzle is physically sitting at 0.3mm (0.1mm gap + 0.2mm movement).
If you level with 0.1mm paper, you are introducing a hidden offset. You are effectively calibrating Z=0 to the top of the paper rather than the bed surface, which often results in poor adhesion due to lack of squish.
A Better Way: The Flashlight Method
Because we want our physical gap to be as close to 0.00mm as possible, visual leveling is often superior to tactile leveling.
We recommend placing a flashlight behind your machine, illuminating the gap between the nozzle and the bed. Adjust your leveling knobs until the nozzle just makes contact with the build plate and the light is blocked.
This establishes a True Z0. The machine now knows exactly where the build surface is.
If you do not have perfect vision or access to good lighting, use the thinnest paper you can find—thermal receipt paper is excellent for this, as it is significantly thinner than standard copier paper.
The closer you can get to a 0.00mm gap during leveling, the more accurate your first layer settings in the slicer will be.
First Layer Thickness and Material Specifics
A pervasive myth in 3D printing is that you should use different leveling mediums for different materials. We often hear advice like: "Use an index card to level for PETG because it needs a thicker first layer."
This is incorrect practice.
You should never use mechanical offsets while leveling to adjust for material requirements. Your Z-offset (the distance from the nozzle to the bed sensor/switch) should be a constant. It represents a physical reality of your machine's geometry.
If you need a thicker first layer for PETG to prevent it from fusing too permanently to your PEI sheet, you should control this in your Slicer Settings.
- Level your bed to True Z0 (using the flashlight or thin paper).
- Open your Slicer.
- Adjust "First Layer Height" (e.g., change 0.2mm to 0.28mm for PETG).
This method keeps your machine calibration consistent while allowing the software to handle the geometry of the print. When you switch back to PLA, you simply change the slicer profile, rather than re-leveling the whole bed.
Never use different thicknesses of paper to achieve different "squish" levels. Adjust the First Layer Height in your slicer instead.
Validation: The Skirt Test
How do you know if you got it right? Use digital calipers.
Most slicers generate a "skirt" (a perimeter line) around your print to prime the nozzle. This skirt is typically one layer tall.
- Peel the skirt off the build plate.
- Measure the thickness with calipers.
- Compare the measurement to the First Layer Height setting in your slicer.
If your slicer is set to 0.20mm and your skirt measures 0.28mm, your nozzle is too far from the bed (likely due to the paper gap we discussed earlier). You can now use the Z-Offset setting on your printer's screen to lower the nozzle by exactly 0.08mm to close that gap.
- Leveling vs. Zeroing: Leveling makes the bed flat; Zeroing tells the printer where the bed starts.
- The Paper Gap: Leveling with paper introduces an offset. If you use paper, expect your first layer to be slightly too thick unless you adjust for it.
- Don't use Index Cards: Never adjust your adjust Z-Offset for specific materials. Use the "First Layer Height" setting in your slicer to create a thicker layer for PETG.
- Trust Calipers: Measuring a printed skirt is the most accurate way to verify your Z-offset.
Should I use feeler gauges to level my bed?
Feeler gauges are excellent because they have a known, consistent thickness. However, you must account for that thickness in your Z-offset. If you level with a 0.1mm gauge, you must set a Z-offset of -0.1mm to compensate.
My first layer is rough and has ridges. What is wrong?
If your first layer feels rough like sandpaper or has "waves" in it, your nozzle is too close to the bed. The plastic has nowhere to go and is being plowed up by the nozzle. Raise your Z-offset slightly.
Can I just change the Initial Layer Height in Cura/PrusaSlicer?
Yes. This is the preferred method for handling different materials. Leave your physical bed leveling alone and increase the Initial Layer Height in the software if you need less squish (e.g., for PETG).
9 comments
I have been struggling with bed adhesion for a week (new to 3d). On a positive note, I have learned a lot in my frustration, but, I could have been doing it with a smile on my face the entire time, had I read this first. Printing must work when people use paper, because, so many people do it, but it did not work for me. Thanks for making the issue clear. I am posting this comment before this next print starts, because, I know it is going to work, and even if it doesn’t, at least I know it isn’t my tramming that is the problem. Thanks again!
Glad I found this article. I haven’t even printed yet but “levelling” a bed, particularly with paper or even a feeler gauge, without creating an offset seemed obscure to me. This is exactly how I thought it should work. So now I have to find the offset setting somewhere & figure out everything else. Cheers !
This information is the same as finding a gold bar.
The way you explained to level and set the right Z-height I’ve never seen that on the internet before, and i have searched all the forums and other websites to gain some true information on how to set my printer the right way.
Thank you for this clear guide.
This information is the same as finding a gold bar.
The way you explained to level and set the right Z-height I’ve never seen that on the internet before, and i have searched all the forums and other websites to gain some true information on how to set my printer the right way.
Thank you for this clear guide.
I’ve been printing since October 2020 and honestly found this very helpful still. Well worded explanations.