On my 17 inch laptop screen a 180mm by 80mm PCB at 100% comes out at 179mm by 79.5mm. Not sure why the exact onscreen scaling matters that much since accurate dimensional measurements can be made using tools in the editor (**M** hotkey or **Edit > Measure** or using the **N** hotkey for the **Dimension** tool on the PCB Tools palette) and any component sizing and fit checking is usually done by printing an assembly drawing 1:1 as a pdf.

@andyfierman thanks, that's great information. It may very well have to do with different display scale settings in Windows. My display settings are for a 15-inch laptop with 1920x1080 resolution and 125% scale. This a fairly common setting for a 15-inch high res display. I suspect the 125% may be affecting the zoom scale. I've written Windows apps before and there are lots of display settings to take into consideration when placing and scaling the screen for the user. I suspect EasyEDA doesn't take it into account. A custom zoom would be a sufficient work-around for me.

@andyfierman and I agree, actual dimensioning would be done by some other means than the display zoom. I just find it to be very convenient as a quick visual check of what the board will look like. The zoom scaling offset affects the layout editing as well as the 2D and 3D rendered views on the display.

@andyfierman just as a quick check, I set my screen scaling to 100% (which makes things in general a little small to read) and now the scaling is just about dead-on. So it is the display settings scale factor that affects it.

I was wondering about trying it on a couple of different PC/OS/monitor setups that I have. Might be interesting to see if there's any difference between  browsers too... :)