PPM to TDS Calculator
Going the other way — a water report says 180 PPM, what will your TDS meter show? About 180. Same 1:1 approximation.
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PPM to TDS Calculator
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Going the other way — a water report says 180 PPM, what will your TDS meter show? About 180. Same 1:1 approximation.
How to use this calculator
- Enter the PPM value.
- Read the approximate TDS.
The formula
Same 1:1 approximation, reversed.
What the units mean
PPM (parts per million) — one part of solute per million parts of the total mixture. The workhorse unit for trace concentrations in water, air, and food.
TDS (total dissolved solids) — everything dissolved in the water, which handheld meters estimate from electrical conductivity.
Worked example
Lab report: 250 PPM → expect ~250 on the TDS meter.
Quick reference
| PPM | ≈ TDS |
|---|---|
| 100 | 100 |
| 200 | 200 |
| 400 | 400 |
Approximate for freshwater.
Where you will actually use this
Lets you predict meter readings from lab reports and vice versa.
- Cross-checking meters against lab reports
- Filter marketing claims
- Aquarium guides
Mistakes that give wrong answers
- Treating it as exact for all water types
Key takeaways
- Formula: TDS ≈ PPM (1:1 for most water sources)
- Remember: Approximate for freshwater.
- Watch out for: Treating it as exact for all water types
- Next step: run your own numbers in the calculator above, then verify with a measurement — calculated values are only as good as the inputs.
Frequently asked questions
How do you convert PPM to TDS?
Use 1:1 for typical freshwater.