Grow Calculator
EC ⇄ PPM Converter
Three competing PPM standards are the most common reason growers accidentally overfeed. Convert between all of them here.
mS/cm
750 ppm
converted value
750 ppm
500 (Hanna / TDS 0.5)
1050 ppm
700 (Bluelab / TDS 0.7)
960 ppm
640 (Eutech / TDS 0.64)
Equivalent EC: 1.50 mS/cm (1500 µS/cm).
Why three scales exist
Meters do not actually measure parts per million. They measure electrical conductivity and then estimate dissolved solids using a multiplier. Different manufacturers picked different multipliers based on different reference salts, and the industry never standardised.
- 500 scale (NaCl / TDS 0.5) — Hanna, most US hobby meters
- 700 scale (KCl / TDS 0.7) — Bluelab, common in the UK and Australia
- 640 scale — Eutech and some lab meters
EC in millisiemens per centimetre is the raw measurement and never ambiguous. When you record a grow journal or read someone else's feed chart, EC is the number worth trusting.
Common questions
- How do I convert EC to PPM?
- Multiply EC in mS/cm by your meter's conversion factor: 500 for Hanna and most US meters, 700 for Bluelab and most Australian and UK meters, or 640 for Eutech. An EC of 1.5 is 750 ppm on the 500 scale and 1050 ppm on the 700 scale.
- Which PPM scale should I use?
- Whichever your meter uses — just be consistent and state it whenever you share numbers. EC is the unambiguous unit, which is why most commercial growers and nutrient schedules have moved to it.
- My feed chart says 1000 ppm but my plants burn. Why?
- Almost always a scale mismatch. If the chart was written on the 700 scale and your meter reads on the 500 scale, matching the number means you are actually feeding 40% stronger than intended.