Size/bleed error of 0,001mm

I think it is a rounding error, too. But one way to test is for the OP to setup a similar test but using Picas and Points instead of Millimeters. If the same procedure gives more rounding errors, something else might be wrong.

Out of curiousity, which Preflight profile are you using that detects this?

This is a rounding artifact, and frankly, nothing to be concerned about because of how minuscule the error is.

You have to remember that any Postscript-based desktop publishing program is based in points, whether you use millimetres as your units or not. So when you work in InDesign with your units to millimetres, there's always a conversion to points (and back) going on in the workflow.

In your case, 400 mm is equal to 1133.85826771776(etc) in points. Although, in reality are converted with only 3 digit or even just 2 digit accuracy, so it could be written in the PDF as maybe 1133.858 or 1133.86. Now, when you view that back in Acrobat, these point values are being converted back to millimetres, again with maybe only 2 or 3 digit accuracy, hence why you are getting numbers like 399.999. In contrast, your 300 dimension converts more cleanly as it converts to 850.394 and then back to 300.000105.., but with the accuracy fudging is back to 300.0 as expected.

It seems weird, but this is actually normal behaviour.

Hi @defaultd1f7p8zddoiy,

Thanks for reaching out! Could you provide the following details to help troubleshoot this issue:

1. Which version of InDesign are you using?
2. What is your operating system (macOS/Windows version)?
3. Is this issue specific to one document, or does it happen with all documents?

This issue may occur due to minor rounding differences in bleed or page size calculations during export. To address this:

• Ensure that your document setup (page size and bleed settings) matches the export settings exactly.
• Double-check the bleed values in File > Document Setup and ensure they match your desired output.
• When exporting to PDF, verify the bleed settings under Marks and Bleeds.

Also, if the issue persists, we would like you to share the file with us for testing. Let me know if these steps help.

Best,
Abhishek Rao