Version: 6.4.4.2 (x64) Build ID: 3d775be2011f3886db32dfd395a6a6d1ca2630ff CPU threads: 4; OS: Windows 10.0 Build 19041; UI render: default; VCL: win; Locale: en-GB (en_GB); UI-Language: en-GB Calc: threaded My Windows 10 laptop resolution is 1366 x 768 px (obtained from the Intel graphics control panel). As the width of the display is 13.5 inches, this gives a DPI = 101. Using "Screen Ruler" (https://sourceforge.net/projects/screenruler/) at this setting, I find that the dimensions of objects in the Writer edit window are actually 5% less than they should be at 100% zoom. Thus, at 100% zoom, a page width settings of 13 cms (Page style > Page) becomes approx 12.5 cms in the edit window, and so on.
Please provide steps for reproduction. Try, please reproduce the bug on the latest version of LibreOffice. Attach some screenshots.
Created attachment 173969 [details] Screenshots of Writer Version: 7.3.0.0.alpha0+ / LibreOffice Community Build ID: c703b2d22c3f45825d9c9d790c3b5a4b6f97e776 CPU threads: 4; OS: Linux 5.4; UI render: default; VCL: gtk3 Locale: en-GB (en_GB.UTF-8); UI: en-US TinderBox: Linux-rpm_deb-x86_64@86-TDF, Branch:master, Time: 2021-06-17_00:44:32 Calc: threaded Laptop screen dimensions are 13.5 ins x 7.6 ins. (measured with a ruler). Screen pixel dimensions are 1366 x 768 pixels (confirmed in the "Display" dialog for Linux Mint). This equals 101 pixels per inch. The width of the page is 12.5 cm according to Linux screenruler (and confirmed with an ordinary ruler laid across the screen). However the width setting in Page Style > Page is 13 cm. See screenshots for confirmation.
LibreOffice has no way of knowing the physical size of the monitor, which would be required to know the real PPI to try to create a "true" size on screen. This is not a bug, because the information that LibreOffice gets from OS, is used correctly (and that is obviously the usual 96 PPI).