It's about sq. feet or sq. meters etc... Shape will impact what you want too - rectangle / square area etc.
I just dropped from 1100w to 720w to cover the same area and i have more photons per square foot by a mile compared to the cheap lights you can find on amazon. If you get the right diodes on the right light, you will blow HPS out of the water and save money every month on your electric bill.
The most efficient diiode out there is the LM301. QBs, strips in a series, solder them yourself... as long as they are genuine.
Too many variables to give specifics. Just look into their umol/J rating. If you can do some algebra, you can convert PAR for your area too. Design it to reach up near limit sans CO2 or with CO2...
If first time growing, get something basic, keep it simple and figure out what you want to do. there may be things you realize after a year that you can't know now. I wouldn't try to grow 10 plants to start - not that it is complexe, but you will make mistakes your first grow that you will never make again. Might as well learn with 1 or 2 and limit damage, lol. 1 plant every 3 months will easily cover any person's smoking habit, if you fill just a 3'x3' area.