I use the elevate plugin for strava (only works on chrome afaik) and it'll figure out the % of time pedalling on a ride. I did a flat 200k yesterday and pedalled 87% of the riding time. On a hillier 400 that I recorded ~3800m on I pedalled 81% of the time. I like to coast when I can, I definitely tuck and coast down any hills that will let me do that.