When exporting an artboard using File > Export > Export for Screens, if the artboards are not aligned to pixel grid, the artboard size increases by one extra pixel.
To align artboards to the pixel grid:
- Choose Object > Make Pixel Perfect.
- Click the Align Art To Pixel Grid On Creation And Transformation () icon in Control panel.
Note: This change will affect artboard contents.
When you export non-aligned artboards, Illustrator highlights them in the Export for screens dialog and also warns you about their non-alignment.
See also: Draw pixel-perfect art
To pixel-align artboards, alternatively you can manually change the X and Y values of the artboard in Properties panel.
For example, consider the artboard of size 600 x 200 and placed at X: 298.28pt and Y: 207.31pt.
If you change the values to the nearest integer 298pt and 207pt, the extra pixel is removed and the artboard is correctly sized at 600 x 200 pt.