Trip planning app

Hi. I am a total newbie, looking at converting to, and building, an ebike. I live in a rural area and the closest shop is 25km or 16 miles ride. It has a total climb of around 450m (1475') but as the route has several up and down sections, the sum of all the climbs will be a lot more. I am wondering if there is a mobile app that will record the gradient data, as I drive the route, so I can then do the math to determine my best setup. I tried a few altimeter apps but they don't have sufficient granularity to be of any use. Most will only sample every 5 minutes or so. I realize that this might already be answered but, I haven't found the right search terms to deliver any answers.

I use the MapMyRide app, and it tracks all elevation changes, but I am not sure how frequently it samples.

Good Luck!

Thanks, TrikeBirder. I am installing it now and will see how it goes.
I found that a lot of apps need internet connection to function but where I want to ride, there is only cell coverage for the last couple of km of the trip.

For future searches, I ended up using Strava and it worked a treat. Unfortunately, my trip to the pub actually has 710m of climb over 25km. Will I make it there and back with my 400W battery? Watch this space

I don't know how accurate it is (garbage in/garbage out obviously), but this is fun to play with:
http://www.electricbikerange.info/Electric_bike_range.html