I have quite a few Sonoff temperature and humidity sensors. When I add them to the dashboard they show up but with only temperature on screen. I also want to change it from F to C, i have changed the setting in the setting page to C but it does not reflect this on the dashboard.
Using the built in dashboard tiles, you need to use separate tiles for temperature and humidity. To display humidity, choose Humidity as the template for the tile:
Not really what you asked about.... but I have it bookmarked and it's a pretty handy reference.
I used it to build a dashboard with all my temp readings.
The unit should match what your hub is set to (in settings). If not, try rebooting the hub. My hub is set to C and all devices report their temperature in Celcius on the dashboard.
A "single tile" can depend on your definition. With a bit of creativity and potentially some guidance, you can layer your tiles to make it look like they are one tile. E.g.:
From memory, this was one tile for the image, one for the Study text, another for the temperature, one for the humidity and one for the grey shading behind the text.