Conversion and Calculation Tables—and Some Explanation

In order to help make communication and conversions between different growers in different countries easier, we felt that a conversion page would be useful. Now, growers can simply plug in the figures they have in order to convert between metric and U.S. measurements, or vice versa. Also, a handy calculation tool is included that will help growers figure generally how much their electricity usage will cost for different wattage lamps.

This page also provides a suitable space to explain the general differences between quantifiable terms used to evaluate nutrient solution. When people, books, and articles describe measuring the overall parts per million (ppm) content of a nutrient solution, the figure they supply can be misleading. The salts used in nutrient solutions can be stated in terms of ppm--that is, a ratio of one part to one million of another. The ppm of a solution has routinely been determined by a ppm meter. This device initially takes an electrical conductivity (EC, measured in mS/cm, milliSiemens per centimeter) reading. (In some parts of the world, this measurement is called conductivity factor, or CF; the EC to CF ratio is 1:10.) Then the ppm meter uses a conversion factor (usually 1 mS/cm EC=700 ppm at 68°F) to provide a ppm reading. However, different nutrient solutions are made up of different ratios and forms of nutrient salts, each of which conducts electricity at a different rate. Therefore, similar solutions could yield different ppm readings. Also, different solutions that are made up of different proportions of mineral salts could yield similar ppm readings. The true ppm of your particular solution at any given time can only be found by a chemical analysis by a laboratory, which is usually prohibitively expensive.

It is the electrical conductivity of a nutrient solution that plant responds to in order to transport minerals. Nowadays, most recommendations and all scientific literature on hydroponic nutrient solutions use EC readings--this will eventually become a universal standard. Temperature levels alter EC readings approximately 2 percent for every degree of difference. However, most quality EC meters automatically compensate the reading according to the nutrient solution's temperature. In general, it's best to trust listed EC levels over ppm.

Conductivity Factor (CF) and Electrical Conductivity (EC)
CF = EC

Degrees Centigrade © and Fahrenheit (F)
°C = °F

Length in Meters (m) and in Feet (ft)
m = ft

Length in Millimeters (mm) and in Inches (in)
mm = in

Area in Square Meters (sq m) and in Square Feet (sq ft)
m2 = ft2

Area in Hectares (ha) and Acres (a)
ha = a

Volume in Liters (l) and Liquid Quarts (qt)
l = qt

Cost of Electricity in Relation to Lamp Wattage
To calculate how much it will cost to run a particular lamp, first find out how much you pay for each kilowatt hour (KWH; 1,000 watts=1 kilowatt); we'll call this figure "W." Then find out how many watts your lamp is and convert it in terms of KWH (a 1000-W lamp=1 KWH; a 400-W lamp=0.4 KWH); we'll call this figure "X." Then find out how long your growing cycle will be each day; we'll call this figure "Y." Then figure out how long the total days of the growing cycle will be; we'll call this figure "Z."

The equation:
((W * X) * Y) * Z = $C
$C will be the estimated total cost of electricity for the lamp in question.

Calculate it!
1. Enter your KWH charge: $/KWH
2. Enter your lamp wattage: watts
3. Enter your daily growing cycle: hours
4. Enter your total growing cycle: days

Your total cost: $

These calculators require JavaScript.

This flash-based Hydroponics Calculator offers many additional useful tools for hydroponics growers, including tools to help you assess wattage, PPM, Carbon Dioxide and more.

Several texts were useful resources while compiling the information on this page, including: