Ok I will not claim to know the answer, but my understanding was that the numbers are a percentage of the fert before dilution.

So if you have 10-25-25 then that is 10% N, and 25% each of P and K. Take 100ml of that and it contains about 10ml N, and 25ml each P and K. Dilute that with 900ml water and you have 10ml N / 1000ml = 0.01% N, and 25ml / 1000ml = 0.025% P and K in the final mix.

They are effectively ratios of N, P and K. I hope this is correct, and until someone more knowledgeable confirms it don't take it as truth.

-canuck :jointsmile: