How to calculate NPK Ratio properly

it's fairly complex. Mulder's chart can help understand relationships between the individual nutrients needed. pH is going to impact what you want vs someone else too. So some local variables add volatility to what you need vs what i need, for example. in vege i'd shoot for something like: 130 ppm N 60+ ppm P 190+ ppm K 100+ ppm Ca 75+ ppm Mg less than 110 ppm S This should be around 1,3 to 1,4 EC. It's fiarly mild concentration for soilless and hydro context. It'd be safe fo autos and photos to start and you can very easily observe and adjust to any slow progressing problems to fine-tune it to your local needs. I have hard water, so you may need more Ca and Mg. Although, when i switched to soft water (convenience), i didn't notice a huge problem. Definitely needed a tad more Ca than before with hard tap water but not all plants showed any symptoms and was very slow in progression. easier to add than take away. Even 130 ppm N my be a bit too much. 120 t0 140 is probably the range you'll roam in to make a particular plant happy. in bloom i don't have to drop this any further than 110ppm N and avoid toxicities. Mg usually needs to be dropped a bit along with it.