# RE: mg/L or Ppm

```The Amazing Metric System

<http://ts.nist.gov/ts/htdocs/200/202/mpo_home.htm>

CGS = centimeter-gram-second system

Volume
“L” is the abbreviation for  “Liter” which is also 1000 cubic centimeters
which is written as cm^3 (never use cc!)

“mL” = milli-Liter = 1/1000 of a liter = 1 cm^3

Length
“m” = meter
“cm” = centi-meter = 1/100 m

Mass
“g” = gram
“mg” = milli-gram = 1/1000 of a gram
1000 g = 1 kg = 1 kilo-gram

Time
”s” = second

Density of water is 1 g/cm^3

1 Liter of water = 1,000 cm^3 of water = 1,000 g of water = 1 kg of water
1 m^3 of water = 100 x 100 x 100 cm^3 = 1,000,000 cm^3
= 1,000 kg = 1 tonne (metric ton)

1 mg of substance dissolved in 1 Liter of water =
= 1 mg/L =
= 1 mg substance in 1,000 g water =
= 1/1,000 g substance in 1,000 g water =
= 1 part substance in 1,000 x 1,000 parts water
= 1 part per million (ppm)

Quiz:
1) 1 g of Potassium in 200 L of water gives you how many mg/L of Potassium?
A: 1000 mg/200 L = 5 mg/L = 5 ppm

2) 1/4 tsp. of Potassium in 55 gallons of water gives you how many ppm of
Potassium?
A: I have no idea.

3) How much Potassium Sulfate does your 55 Gallon plant tank need?
A:  A big pinch every couple of days.  Try more or less and see what
happens.

(and let’s not get into how much K is in 1 g of K2SO4!)

```