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NTU vs. FTU: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on February 5, 2024
NTU (Nephelometric Turbidity Unit) measures water clarity based on light scattering, while FTU (Formazin Turbidity Unit) is a standard scale for turbidity calibration.

Key Differences

NTU, or Nephelometric Turbidity Unit, is a measure of water turbidity using a nephelometer, which assesses the scattering of light in water. FTU, Formazin Turbidity Unit, serves as a calibration standard in turbidity measurement, based on a formazin suspension.
NTU values indicate the cloudiness or haziness of water, crucial in water quality assessment. FTU is utilized to calibrate turbidity measuring instruments, ensuring their accuracy in measuring turbidity in NTU or other scales.
In NTU measurements, higher values correspond to greater turbidity, reflecting more particles in the water. FTU is formulated to provide a consistent turbidity reference, with known FTU values replicating specific turbidity levels.
NTU is commonly used in environmental monitoring and water treatment processes. FTU, being a calibration tool, is essential in laboratories and for instrument manufacturers to standardize turbidity measurements.

Comparison Chart


Measures water turbidity
Calibration standard for turbidity


Light scattering in water
Based on formazin suspension


Water quality assessment
Instrument calibration


Higher values mean more turbidity
Known values replicate turbidity levels


Environmental monitoring, water treatment
Lab testing, instrument standardization

NTU and FTU Definitions


Indicates water clarity.
A low NTU value means clearer water.


Used in laboratory settings.
The lab uses FTU for consistent results.


Used in environmental testing.
The NTU levels were monitored daily.


Standard scale for turbidity.
The instrument was calibrated to 5 FTU.


Reflects particulate matter in water.
Increased NTU can indicate pollution.


Essential in instrument calibration.
Regular FTU checks ensure measurement precision.


Unit for measuring water turbidity.
The river's NTU reading indicated high turbidity.


Based on formazin suspension.
FTU uses a formazin standard for accuracy.


Assessed using a nephelometer.
NTU measurements require specialized equipment.


Replicates specific turbidity levels.
FTU values help standardize turbidity readings.


Can NTU values indicate water quality?

Yes, NTU values are critical indicators of water quality.

What is FTU used for?

FTU is used for calibrating turbidity measuring instruments.

What does NTU measure?

NTU measures the turbidity or cloudiness of water.

Is FTU a universal standard?

Yes, FTU is a widely accepted standard in turbidity measurement.

How is NTU measured?

NTU is measured using a nephelometer.

What is the basis of FTU?

FTU is based on a formazin suspension standard.

Can NTU readings change rapidly?

Yes, NTU can change with varying water conditions.

What affects NTU readings?

Particulate matter, algae, and sediment can affect NTU.

Is FTU only used in laboratories?

Primarily, though it's also used in industrial settings.

How accurate is FTU?

FTU provides a high level of accuracy in calibration.

Are higher NTU values good?

No, higher NTU values indicate poorer water clarity.

Is FTU important for water treatment?

Yes, FTU calibration is essential for accurate water treatment processes.

Are NTU and FTU interchangeable?

No, they serve different purposes in water analysis.

Can NTU detect all types of water contaminants?

NTU detects particulates, but not all types of contaminants.

Can FTU be used in field testing?

FTU is mainly for lab and instrument calibration, not field testing.

Is NTU affected by color?

NTU focuses on turbidity, not color, though color can impact readings.

Do NTU levels affect water treatment?

Yes, water treatment processes are adjusted based on NTU levels.

Does FTU apply to all turbidity meters?

Yes, FTU standards are applicable to various turbidity meters.

Why is FTU important in quality control?

FTU ensures consistency and accuracy in turbidity measurements.

Is FTU calibration a one-time process?

Regular calibration using FTU standards is necessary for precision.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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