Calculating area's region in DEM

I have a DEM map in my project Tsunami Assesment project.The white area below the mentioned map is sea and we know that possible tsunami height is 14 meters(please neglect the line, there is an error in the data).So i have divided my DEM into 2 zones: the areas which have height of 14+ meters (in pink) and the ones below it (inundation zones-in blue).

How do I calculate how many m^2 is inundated (below 14 meters) and what percent of study area does it cover?

1. Use raster calculator to create a binary raster (black&white; 0&1) with this expression: `raster_layer_name@1 < 14`. Areas below 14 m will appear in white (=1), all areas above in black (=0).
2. Use `Menu Processing > Toolbox > Contour polygons` (from GDAL provider) and set the Interval between contour lines to 1.
3. You get a polygon layer with two features: one multipart polygon for areas below 14m, the other multipart feature for those above. Calculate the respective areas, e.g. with Field calculator and the expression `\$area`.