NPK Ratios Calculation

Hello All,

I have been trying to wrap my head around NPK ratios so I created a spreadsheet to help me sort it out. I do realize there are a lot of variables which makes straight forward math tough but how far do you think this is off?

I started with the recommended dosage and calculate the actual volume of NPK as a percentage:

By adjusting the dosage percentage I can change the final NPK ratio:

So in this case I was shooting for 2-3-4. I am 4 weeks into an 8 week flower using soil. I starved them a lil for nitrogen hence the 2 ratio. The final EC of my feed came out to 2.1.

Like I said earlier, on stuff like this 2+2 doesn’t always equal 4.

I would appreciate your thoughts.


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I don’t know any growers who pay any attention to NPK ratios at this level. Most will just feed a percentage of the recommended schedule and count on the manufacturer to get the ratios correct for a healthy plant. I have fed 50% of the nute manufacturer schedule (Fox Farm Trio + flowering boosters) over dozens of plants and have never had an issue other than having to flush salts out of the soil once each grow.

Increasing nutes beyond the recommended schedule often leads to nute burn. In fact, most manufacturer schedules need to be reduced to avoid nute burn.


Don’t over think it. It is a weed, All it wants is something to drink and eat.

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I think hydro buddy could help you with this.

Nice! Thank you… it should be fun digging into this software.