eCalc is a very useful tool when calculating on weight, motors, batteries, ESC, propellers and more for your multicopter. It provides a huge database with different parts and hardware for your multicopter. You simply choose what parts you are planning to use, and eCalc will then calculate all the data.
Maybe it’s not 100% accurate or reliable, but it will definitely give you lot’s of useful information for your multicopter projects.
It’s free to use (non commercial), but you can donate a few bucks if you like it and if you want to encourage this kind of projects.