You can use the calculator, but try to find out what the screen gain is. What is the model exactly?It's a generic motorized screen with grey projection area to reduce washed out blacks I was having with a complete white screen.
I do have a smarphone and I've tried some apps to measure lumens but are those reliable?
If you have some app suggestion I can try here.
I was watching Rear Window 4K and the image seemed a little dull. I know my projector can do much more vibrant colors.
To sum it up what I need to do is get a real measure from my screen and increase dynamic target nits for a more vibrant picture?
Using a smartphone app is better than nothing.
Just search for lux meter app.
1 lux = 0.092903 fc.
Measure the lux right in front of the screen, with the phone's screen facing towards the projector, not the screen.
Then add the screen gain.
For further support, use this thread: