Renfro
Well-Known Member
Understanding and Calculating Nutrient PPM
PPM (Parts Per Million) can seem like a mystery but it’s actually very simple. Basically the idea is to quantify how much “stuff” is in your water.
PPM is commonly measured by a grower using an electronic pen which measures the electrical conductivity of the water (EC). This is then converted to a PPM number with a conversion factor. Since different substances in the water will conduct electricity with varying degrees of resistance we must understand this number is only an estimate.
This is all fine and dandy for figuring out how much of everything is in your mix but what if you want to get more specific and determine how much of a given nutrient is present in your mix.
If we want to calculate how much of a given nutrient is in the mix using the label ingredient percentages we can make that happen with a little math.
Dry Salts - Mass Measurements
Say we are adding half a gram of Calcium Nitrate to 1 Liter of H2O and we want to see how much calcium and nitrogen we added in PPM, we know the calcium nitrate is 19% Calcium.
500mg x 0.19 = 95 mg/L (ppm) Calcium
500mg x 0.155 = 77.5 mg/L (ppm) Nitrogen
To do the math for 1 gram per gallon,
First get the mg per liter from gram per gallon:
1000mg / 3.785 = 264.2007926023778
Grams per Gallon x 264.2007926023778 x Label Percentage = PPM
Calcium Nitrate is 15.5% Nitrogen therefore we get,
1 gram x 264.2 x 0.155 = 40.95 PPM
of nitrogen by adding 1 gram to a gallon.
So for basic dry (mass) calcs just take 264 times the percentage and you know how many PPM of something you get with a gram per gallon.
The calcium nitrate also has 19% calcium.
1 gram x 264.2 x 0.19 = 50.19 PPM
of calcium by adding 1 gram to a gallon.
To figure out how much of something to add to get a given PPM you divide the target PPM by the percentage
So lets say you want 40 PPM of Magnesium from Epsom salt. Epsom is 9.7% Magnesium and 13% Sulfur.
40 / 0.097 = 412mg/L
and
412 x 3.785 = 1560.8mg or 1.56 grams per gallon to get 40 PPM of Magnesium.
Now that also brings some sulfur and we can calculate that,
412mg/L times 0.13 = 53.56 PPM
of Sulfur comes along with the 40 PPM of magnesium.
Phosphorous and Potassium - Beasts of another nature
It should be noted that P & K are different animals depending on how they are put in the mix.
By convention in the U.S. the fertilizer label lists the percentage P2O5 instead of the percent P. Similarly, the labels lists the percentage K2O instead of the percent K. This means we have to take into account conversion factors to calculate the percent elemental P and K.
To convert P2O5 to P multiply by 0.4364
To convert P to P2O5 multiply by 2.2915
To convert K2O to K multiply by 0.8301
To convert K to K2O multiply by 1.2047
Liquid Nutrients and Specific Gravity - Volume Measurements
It gets more complicated when mixing by volume and not mass, liquid nutrients. In this case you must take density into account.
Since the specific gravity of a nutrient isn't commonly listed on the label we must weigh a volume of the nutrient and calculate it's specific gravity.
For example, I just put 100mL of GH Micro in a graduated cylinder and it weighed about 121.2 grams. So if I do some math on the GH micro, 1mL per gallon, the label says it has 5% calcium.
1 mL per gallon x 264.2 x .05 = 13.2 PPM of calcium
BUT when we take into account the extra mass in the mL we multiply that by a specific gravity of 1.212 (according to my most likely not accurate measurement) and then we get 16 PPM of calcium by adding 1 mL of Micro to a gallon of water.
1 mL per gallon x 264.2 x .05 x 1.212 = 16 PPM of calcium
I hope this helps explain PPM and I regret any errors in my math. Please contribute if you see anything important I missed or any unfortunate errors in my work. I didn't go into conversions of PPM from EC as thats really another subject and very simple. - Renfro
PPM (Parts Per Million) can seem like a mystery but it’s actually very simple. Basically the idea is to quantify how much “stuff” is in your water.
PPM is commonly measured by a grower using an electronic pen which measures the electrical conductivity of the water (EC). This is then converted to a PPM number with a conversion factor. Since different substances in the water will conduct electricity with varying degrees of resistance we must understand this number is only an estimate.
This is all fine and dandy for figuring out how much of everything is in your mix but what if you want to get more specific and determine how much of a given nutrient is present in your mix.
If we want to calculate how much of a given nutrient is in the mix using the label ingredient percentages we can make that happen with a little math.
Dry Salts - Mass Measurements
Say we are adding half a gram of Calcium Nitrate to 1 Liter of H2O and we want to see how much calcium and nitrogen we added in PPM, we know the calcium nitrate is 19% Calcium.
500mg x 0.19 = 95 mg/L (ppm) Calcium
500mg x 0.155 = 77.5 mg/L (ppm) Nitrogen
To do the math for 1 gram per gallon,
First get the mg per liter from gram per gallon:
1000mg / 3.785 = 264.2007926023778
Grams per Gallon x 264.2007926023778 x Label Percentage = PPM
Calcium Nitrate is 15.5% Nitrogen therefore we get,
1 gram x 264.2 x 0.155 = 40.95 PPM
of nitrogen by adding 1 gram to a gallon.
So for basic dry (mass) calcs just take 264 times the percentage and you know how many PPM of something you get with a gram per gallon.
The calcium nitrate also has 19% calcium.
1 gram x 264.2 x 0.19 = 50.19 PPM
of calcium by adding 1 gram to a gallon.
To figure out how much of something to add to get a given PPM you divide the target PPM by the percentage
So lets say you want 40 PPM of Magnesium from Epsom salt. Epsom is 9.7% Magnesium and 13% Sulfur.
40 / 0.097 = 412mg/L
and
412 x 3.785 = 1560.8mg or 1.56 grams per gallon to get 40 PPM of Magnesium.
Now that also brings some sulfur and we can calculate that,
412mg/L times 0.13 = 53.56 PPM
of Sulfur comes along with the 40 PPM of magnesium.
Phosphorous and Potassium - Beasts of another nature
It should be noted that P & K are different animals depending on how they are put in the mix.
By convention in the U.S. the fertilizer label lists the percentage P2O5 instead of the percent P. Similarly, the labels lists the percentage K2O instead of the percent K. This means we have to take into account conversion factors to calculate the percent elemental P and K.
To convert P2O5 to P multiply by 0.4364
To convert P to P2O5 multiply by 2.2915
To convert K2O to K multiply by 0.8301
To convert K to K2O multiply by 1.2047
Liquid Nutrients and Specific Gravity - Volume Measurements
It gets more complicated when mixing by volume and not mass, liquid nutrients. In this case you must take density into account.
Since the specific gravity of a nutrient isn't commonly listed on the label we must weigh a volume of the nutrient and calculate it's specific gravity.
For example, I just put 100mL of GH Micro in a graduated cylinder and it weighed about 121.2 grams. So if I do some math on the GH micro, 1mL per gallon, the label says it has 5% calcium.
1 mL per gallon x 264.2 x .05 = 13.2 PPM of calcium
BUT when we take into account the extra mass in the mL we multiply that by a specific gravity of 1.212 (according to my most likely not accurate measurement) and then we get 16 PPM of calcium by adding 1 mL of Micro to a gallon of water.
1 mL per gallon x 264.2 x .05 x 1.212 = 16 PPM of calcium
I hope this helps explain PPM and I regret any errors in my math. Please contribute if you see anything important I missed or any unfortunate errors in my work. I didn't go into conversions of PPM from EC as thats really another subject and very simple. - Renfro
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