Understanding the language of PPM (parts per million) is essential in water testing, hydroponics, chemistry, and environmental science.
This glossary provides clear definitions of key terms used in PPM measurement, testing, and conversion—so you can interpret lab data confidently and use the right tools for accurate results.
PPM Fundamentals
Parts Per Million (PPM)
PPM measures how many parts of a substance exist in one million parts of another.
In most cases, 1 PPM equals 1 mg of solute per liter (mg/L) of solution.
If you’re new to this concept, see our detailed guide on what PPM means and why it matters.
Parts Per Billion (PPB)
PPB is a finer measurement—1 PPM equals 1,000 PPB. It’s used when analyzing trace contaminants in water or air.
To convert between these two units easily, try the PPM to PPB Calculator on our site.
Milligrams per Liter (mg/L)
In liquid measurements, mg/L and PPM are equivalent. Most lab reports use mg/L to express chemical concentration in water quality testing.
Electrical and Conductivity Terms
Electrical Conductivity (EC)
EC shows how well a liquid conducts electricity, which depends on its dissolved ions.
It’s expressed in µS/cm (microsiemens per centimeter) or mS/cm (millisiemens per centimeter).
For accurate conversion between EC and PPM, use our EC to PPM Calculator and learn more in PPM vs. TDS vs. EC Explained.
Total Dissolved Solids (TDS)
TDS measures all the minerals, salts, and metals dissolved in water.
Although it’s displayed in PPM, TDS is broader than a single chemical concentration.
High TDS affects both water taste and conductivity. You can estimate TDS from EC readings using the TDS to PPM Calculator.
Microsiemens (µS/cm)
The base unit for conductivity readings.
One microsiemens equals 0.001 millisiemens.
Hydroponic growers and lab analysts monitor µS/cm to keep water quality consistent.
Chemistry and Lab Measurement
Molarity (mol/L)
Molarity represents the number of moles of solute per liter of solution—a key unit in chemistry and lab formulation.
To translate molarity into PPM, check our PPM to Molarity Calculator for a quick, accurate conversion.
Titration
A classic method where a reagent of known strength reacts with a sample until an endpoint is reached.
Used to determine acidity, alkalinity, and chlorine content.
You can explore how this technique relates to PPM in How PPM Is Measured in Labs.
Spectrophotometer
A precision device that measures how much light a solution absorbs at specific wavelengths, helping identify concentration levels in substances such as chlorine or nitrates.
Water and Environmental Testing
Water Hardness
Indicates the calcium and magnesium ion levels in water, typically expressed in mg/L as CaCO₃.
To convert hardness from PPM to other units, use our PPM to Water Hardness Calculator.
Turbidity (NTU)
Measured in Nephelometric Turbidity Units (NTU), turbidity reflects how cloudy water is because of suspended particles.
Environmental and wastewater labs often use the PPM to NTU Conversion Calculator to compare readings.
Salinity
Refers to the total dissolved salts in water, expressed in PPM or parts per thousand (PPT).
This value is especially relevant for aquariums and marine testing, and you can convert salinity with our PPM to PPT Calculator.
Chlorine Concentration
Shows how much free or total chlorine exists in a sample.
For everyday use, the Chlorine PPM Calculator and Pool Chlorine PPM Calculator make quick, accurate testing easier.
Dissolved Oxygen (DO)
Measures the amount of oxygen dissolved in water, vital for aquatic life and plant growth.
Convert DO readings effortlessly with the PPM to Dissolved Oxygen Calculator.
Agriculture and Hydroponics
NPK Ratio
Describes the balance of nitrogen (N), phosphorus (P), and potassium (K) in fertilizers.
Use the NPK PPM Calculator to calculate precise nutrient concentrations.
Nutrient Solution
A mix of water and essential minerals used to feed plants in hydroponics.
Maintaining balanced PPM levels ensures steady growth. Learn more in our article PPM in Hydroponics: A Beginner’s Guide.
Fertilizer Strength
Shows how concentrated your nutrient mix is, usually expressed in PPM or EC.
The Fertilizer PPM Calculator can help prevent overfeeding and nutrient lockout.
Industrial and Quality Control
CPK (Process Capability Index)
Used in manufacturing to evaluate how consistent a process is.
The PPM to CPK Calculator converts between quality control values and defect rates.
Six Sigma (Defects Per Million)
A benchmark for production quality—achieving Six Sigma means only 3.4 defects per million.
You can explore this concept with the Six Sigma PPM Calculator.
Accuracy and Precision
Accuracy describes how close a measurement is to the true value; precision reflects repeatability.
Test your tolerance limits using the PPM Accuracy Calculator.
Quick Reference Conversions
| Conversion | Formula |
|---|---|
| EC → PPM | EC × 0.5 to 0.7 |
| mg/L ↔ PPM | Equivalent |
| PPM → PPB | × 1,000 |
| PPM → PPT | ÷ 1,000 |
Bookmark these relationships when analyzing lab or field data—they’ll save time and reduce errors.