Filter advise or app

Im starting to use Lee Neutral density soft and hard grad filters more and more, so am i correct with my method, expose for the foreground expose for the sky and work out the difference to see which ND filter to use? if the method im using is correct does anyone know an app for calculating the difference and telling you which ND filter to use?

Use a spot meter, or the spot meter function of your in-camera meter.

Your method is correct. LExp - Long Exposure is an app. for iPhone that I use... You dial in the exposure for both and it tells you which ND Grad to use... or combinations of grads

Just had a look at the features of the app it's what I'm looking for but unfortunately it's only available for iPhone.

Sent from my CLT-L09 using Tapatalk

You might want to check out https://play.google.com/store/apps/details?id=com.iioannou.ndcalculator&hl=en_US

Photo Tools.

You could print out an exposure chart and carry it in your bag. Just take a reading of the sky and another of the ground then figure out the difference. This one covers f/stop, shutter speed, and ISO stops.