When fertilizing, what's the difference between ppm and g/L??

[camille1585]

I have a really dumb question about fertilizing here... What is the link/difference between ppm and grams per liter?? Somehow I know that the answer will be very obvious once I hear it....
In France it seems like g/L is the preferred (and nearly only) measure. We always speak about fertilizer in g/L.
I get a little lost in the threads sometimes when you speak of feeding your orchids!! Anyone care to enlighten me?

[shakkai]

If there is a direct conversion, I'm not aware of it. The way I understand it, 'ppm' is a relative calculation - so no litre, or other specified volume... just a 'million parts' so 1ppm is 1 part (of whatever is being measured) per 1 million parts of something else. Though an estimate can be made of 1 milligram per litre (mg/L) - which would be 1 millionth of a litre = 1ppm. But that only works for water, as 1L of water is defined as 1Kg (or vice versa).

[Ross]

Hey, Ray! We're all ears here!

[quiltergal]

PPM is how you measure the concentration of a solution. G/L or tsp/gal are just ways that you arrive at that concentration.

[Jerry Delaney]

Here you go!

Grams/Liter to Parts/Million (Ppm) Conversion Calculator

[camille1585]

I've been reading up on this on french websites to try to understand...
I looked at the converter, but I'm thinking that it's missing something. Isn't 1g/l of 20-20-20 going to have a heck of a lot more ppm than the 1g/l of 5-5-5 for example??
Keeping to the same example, how do you calculate the ppm of a 20-20-20 fertilizer?

I'm feeling from so much thinking!!

[quiltergal]

Camille you are correct. 1 gram/liter of 20-20-20 has a much higher PPM of N than 1 gram/liter of 5-5-5. Ray has a calculator on his website where you plug in the number of N and your target PPM and it will calculate how many tsp/gal or ml/l you need to reach the target PPM. It's down at the very bottom of this page. You should be able to convert g/l to ml/l. In your example of 20-20-20, if your targeted ppm is 125 (which is what Ray suggests) you would need .62 ml/l to reach 125 ppm N. In the 5-5-5 example you would need 2.47 ml/l to reach 125 ppm. Hope this helps!

Fertilizer PPM Calculator

[Ray]

Hi, Camille.

A part-per-million (ppm) is equivalent to a milligram per kilogram. However, don't confuse the total mixing ratio (g/L) with the concentration of a specific component.

In most of the "what fertilizer concentration" discussions, I tend to use the nitrogen concentration only, and let the rest of the elements follow as they will from the fertilizer's overall makeup (I learned that from large-scale commercial nurseries).

As the nitrogen content is listed on the label as weight percent, the 5-5-5 is 5% (5 parts per hundred or 50 parts per thousand) N, so if a gram of that fertilizer was put in a kilogram of water (a liter), it would giver us a 50 ppm N solution (and the 20-20-20 would give 200 ppm N).

So, when I say I want 125 ppm N in my final solution, that would be 2.5 g/L of the 5-5-5 and 0.625 g/L of the 20-20-20.

[Ross]

Thank you Ray, I just knew you'd have the correct answer to this question.

[camille1585]

Thanks so much everyone for explaining things! And thanks Ray, for your very clear and understandable post. Now I'll actually be able to understand it when you guys discuss stuff like this...
I think I'll go calculate to see exactly what I've been feeding my poor orchids. They're probably starved!