Understanding and Calculating Nutrient PPM

Renfro said:

v1.3

Also added some more products while my buddy and I were messing with his nute mix.

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TreeFiddy350 said:

When I get home tonight, I’ll mess with this and add a few of my nutrients in there

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Renfro said:

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

Click to expand...

Renfro said:

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

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Trout2012 said:

Is there a way to tell exactly what elements are in say well water before the addition of the nutes? They say our water contains a high amount of calcium here! Awesome info here!!!

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Renfro said:

You can send a sample of your well water off and have it tested.

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Trout2012 said:

Ok thanks I'm just getting into the ppm stuff just bought a meter tested my water today. Out of faucet was 132 is that fairly normal?

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Trout2012 said:

fountain it clogged up with white stuff in just a few months

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Trout2012 said:

I know their well is the old point style and shallow. I had a new well put in about 11 years ago, it 79 feet deep. My other well just quit flowing slowy. Probably clogged with what ever it is!!

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