Turbidity to TSS Converter
Turbidity meters read NTU. Discharge permits and most laboratory methods are written in mg/L. There is no universal number that converts one to the other, because the correlation depends on particle size, shape, colour and refractive index of the solids in your water. What this calculator does is make the factor explicit — and show you how to determine your own.
TSS from turbidity
Estimated suspended solids screening only
Why there is no universal NTU to mg/L factor
A nephelometer measures light scattered at 90 degrees. That response depends on how large, how shaped and how refractive the particles are. A gram of fine clay scatters very differently from a gram of sand, at the same mass. This is why regulatory methods keep turbidity and suspended solids as separate parameters rather than treating one as a proxy for the other.
Published benchmark correlations exist — roughly 1.0 to 2.0 mg/L per NTU depending on water type — and they are useful for estimating, not for reporting.
Benchmark correlations by water type
| Water type | Benchmark factor | Typical NTU | Turbidity meters (NTU) |
|---|---|---|---|
| Treated drinking water | 1.0 – 1.5 | 0.3 – 2 | 0.01 – 10 NTU, low range |
| Raw surface water | 1.5 – 2.0 | 5 – 100 | 0.01–100 NTU with switch |
| Post-sedimentation basin | 1.0 – 1.5 | 1 – 10 | 0.01–10 NTU, low range |
| Final effluent (reclaimed) | 1.0 – 2.0 | 1 – 20 | 0.01–100 NTU |
| Stormwater / runoff | site-specific | 20 – 500 | 0–1000 NTU dual range |
| Industrial high solids | site-specific | 500 – 5000 | Switched range + dilution |
Determining your site-specific factor
The defensible method takes one afternoon. Collect a representative sample from the exact discharge point. Measure NTU in the field with a calibrated meter. Send a second portion to a laboratory for certified gravimetric TSS by EPA 160.2 or Standard Method 2540 D. Divide the laboratory result by your field reading, and you have a factor that is valid for that water.
Do this across a few conditions — wet weather, dry weather, first flush — and if the factor varies, you have learned something important: a single NTU reading is not a reliable TSS estimate for your discharge.
What turbidity range to specify
Range selection is driven by the concentration you need to resolve, not by the maximum possible. Potable water targets below 1 NTU need a low-range sensor with 0.01 NTU resolution. Wastewater clarification typically runs 5–50 NTU, so a 0–100 NTU range is appropriate. High-solid industrial streams can reach thousands of NTU and need a switched or dual-range instrument with automatic dilution.
Instruments for this measurement
Models shown are representative families, not a complete catalogue. Send us your application, water analysis and installation constraints and we will match instruments to it.
Frequently asked
How do you convert NTU to mg/L of TSS?
Is 1 NTU equal to 1 mg/L?
Can a turbidity meter replace a TSS measurement for permit reporting?
Why does my turbidity reading fall after filtration but the laboratory TSS barely changes?
Does NTU depend on the instrument light source?
This page provides calculation guidance and a screening cross-check. It is not a substitute for the measurement method named in your permit, and values shown are typical ranges rather than guarantees for a particular instrument.
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