Hi pal. Did a bit of research for you. Have a look at this and you should be able to come up with a rough time with ok math skills. https://www.co2meter.com/blogs/news/41003521-co2-calculator-for-grow-room-or-indoor-greenhouse anything else is really just a guess, this deals with most factors and temp, amount of plants, stages of growth will all effect the co2 usage. Happy growing.