This one is useful as well. Both the link Nexogen gave and this one are on Ray's website. This one does things the other way around, you put in the NPK from the bottle/packet and the target PPM you want and it tells you the tsp/gal.

Fertilizer Mixing Calculators

Thanks Rosie. Just wish I knew the formula just for my own info.

Robert

teaspoons/gal - Target ppm N / (13.1925 x %N on label).

There is also a very easy rule-of-thumb guide you can use, and that is to divide the factor below by the %N on label, giving you the teaspoons/gal for 100 ppm N.

The numerators by ppm are:

50 - 4
75 - 6
100 - 8
125 - 10
150 - 12
175 - 14
200 - 16

In the case of your 20%N formula, your other calculator had you applying 2 tsp/gal, or 500 ppm N (probably close to 3000 ppm TDS), which would surely have killed some more sensitive plants, and damage the roots of most.

Thanks Ray, I'll keep this in mind (and in My Favorites box).

Robert