Try the app Stockwood (available for free on AppStore and Google Play). You can input up to 24 different cutting lengths, up to 3m in length, and get the cutting lengths adjusted to the stock lengths offered by the supplier. The waste with this calculation is often under 5%. It's probably the best optimization you can achieve at the moment. Then you just have to learn to account for potential miters and not turn the folding rule upside down 😉