TDS Meter PPM Converter
Most handheld TDS meters do not measure TDS at all — they measure conductivity and multiply by 0.64. So "320 PPM" on the display really means 500 µS/cm of conductivity. This shows you the math your meter hides.
Calculator
TDS Meter PPM Converter
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Most handheld TDS meters do not measure TDS at all — they measure conductivity and multiply by 0.64. So "320 PPM" on the display really means 500 µS/cm of conductivity. This shows you the math your meter hides.
How to use this calculator
- Enter EC in µS/cm (or work backward from the display).
- See the 640-scale PPM.
- Learn the limits of the estimate.
The formula
Displayed PPM = EC (µS/cm) × 0.64 on most consumer meters.
What the units mean
µS/cm — microsiemens per centimeter, the unit of electrical conductivity (EC) that meters actually measure before converting to a PPM estimate.
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.
Worked example
Meter shows 256 PPM → it measured about 400 µS/cm of conductivity.
Quick reference
| EC (µS/cm) | Meter PPM (640) |
|---|---|
| 156 | 100 |
| 312 | 200 |
| 781 | 500 |
640 scale used by most handheld meters.
Where you will actually use this
Understanding the estimate stops you from treating a $15 meter like a lab analysis.
- Understanding meter readings
- Comparing meters
- Explaining results to customers
Mistakes that give wrong answers
- Treating the display as a real chemical analysis
- Comparing meters with different scales
Key takeaways
- Formula: PPM ≈ EC × 0.64 (640 scale, common for TDS meters)
- Remember: 640 scale used by most handheld meters.
- Watch out for: Treating the display as a real chemical analysis
- 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
Why do two TDS meters disagree?
Different conversion scales (0.5 vs 0.64 vs 0.7).
Is a TDS meter accurate?
For tracking changes, yes. For absolute chemistry, no.