What exactly do I measure at each corner?

With the nozzle at a fixed Z height above the bed (the same height at every corner), slide a feeler gauge or a strip of paper underneath it until you feel slight resistance. The gap is the gauge reading, or the number of paper sheets times their thickness.

Why does one corner always end up needing 0 shim?

That corner has the smallest measured gap, meaning the bed is physically closest to the nozzle there, its highest point. You can only add material under a corner to raise it, not remove bed material, so every other corner is shimmed up to match that reference point.

What if the calculated shim values are all under 0.05 mm?

Differences that small are usually within what your normal bed leveling screws can take up on their own. Shimming is meant for cases where the screw range is exhausted or the bed itself is physically warped.

Can I really use paper or an index card as a shim?

Yes. Standard printer paper is close to 0.10 mm per sheet, and a typical index card is closer to 0.30 mm. Set the shim material thickness field to match what you plan to use so the recommended sheet count is accurate.

Does this replace normal bed leveling before every print?

No. Routine leveling with the bed screws or an auto-leveling probe still handles small day-to-day drift. This tool is for the specific case where a warp or uneven mount is bigger than the screws can correct, and you need a physical shim under the bed.

Bed Leveling Shim Calculator

Name: Bed Leveling Shim Calculator
Availability: InStock
Author: Nham Vu

Enter the measured gap at each bed corner and get the exact shim thickness to add so the bed sits level.

Corner Measurements

Measurement unit

Front-Left gap

Front-Right gap

Back-Left gap

Back-Right gap

Include a Center reading (large or CoreXY beds)

Shim Recommendation

Enter all four corner gaps to see shim thickness per corner

Summary

Enter the measured gap at each bed corner and get the exact shim thickness to add so the bed sits level.

How it works

Set the nozzle to a fixed test height and slide a feeler gauge, or a strip of paper, under it at each corner until it just drags.
Enter the gap you measured at Front-Left, Front-Right, Back-Left, and Back-Right, either directly in mm or as a count of paper sheets.
Optionally add a Center reading for large or CoreXY beds that tend to sag in the middle.
The calculator treats the corner with the smallest gap as the reference, since that is the highest point of the bed.
Every other corner gets a shim thickness equal to its gap minus the reference gap, so building it up brings the whole bed level.

Use cases

Correcting a warped glass or PEI sheet that the leveling knobs cannot fully compensate for.
Leveling a bed on a printer with fixed, non-adjustable corner mounts.
Checking whether the center of a large bed needs a support shim to stop sagging.
Working out exactly how many sheets of standard paper to stack as a permanent shim.
Comparing before/after corner gaps after re-tramming a bed.

Frequently Asked Questions

Last updated: 2026-07-21 · Reviewed by Nham Vu