This app was mentioned in 2 comments, with an average of 1.00 upvote
For projects like this, I've always used a segment calculator online or an app on my phone. They work great and I don't have to worry about my shitty math skills.
here you go http://www.turnedwood.com/
and a handy phone app
https://play.google.com/store/apps/details?id=com.byroid.segmentcalculator1&hl=en