My grids aren't displaying in degrees in QGIS

A common cause of this problem is using a non-geographic crs for your grid lines.

Typically, you'll want to use a CRS that measures in metres, miles or kilometres for your spatial analysis. While these units are great for analysis and reporting, they're not the best for designing maps. Imagine a map that measures/displays its longitudes and latitudes in metres, miles or kilometres.

So, now we are at a t-junction and are confused which direction to take; use a geographic crs and risk incorrect result but neat/interpretable map layout or use a non-geographic result and get reliable results but poor/unreadable layout.

Luckily for us, there's a way around this. Firstly, use any CRS of your choice for your analysis. Secondly, when you get to the print composer and add grids to your map (as explained in this article; https://geoafrikana.com/how-add-grids-and-grid-frame-map-qgis ), click the modify grid button, under the "appearance" section, you'll see a a drop-down box labeled "CRS". Click it and select a geographic CRS (EPSG 4326).

Voila! Now your grids will display in the degrees not metres, miles and kilometres.