I'm a fairly new user to QGIS and was trying to generate a map of Iceland. However my grid scales are not matching up. The base map I'm using is Esri National Geographic which uses CRS- EPSG:3857 - WGS 84 / Pseudo-Mercator - Projected
The rough width of Iceland is 500km but according to the grid boxes QGIS generated in Print Layout its about 1000km. In grid properties they are set to be 5000000m x 500000m. And the scale bar is not accurate either.