free calculator
EC / PPM Converter
Enter your meter reading — in EC (mS/cm) or PPM — and pick the scale. The calculator converts instantly and shows the equivalent reading in the other unit and scale.
convert EC → PPM: —
convert PPM → EC: —
Why there are two scales — and how to stay on track
EC is the real measurement; PPM is an estimate
Your meter doesn't measure "dissolved particles" directly — it measures the solution's electrical conductivity (EC, in mS/cm or µS/cm). PPM (parts per million) is an estimate calculated from that reading, using a conversion factor that varies from manufacturer to manufacturer — and that's where the confusion starts.
The difference between the 500 and 700 scales
Meters on the "500" standard (Hanna, Bluelab, Truncheon — most of the market) use a factor of 0.5: 1.0 mS/cm becomes 500 PPM. Meters on the "700" standard (some European models, calibrated with KCl) use a factor close to 0.7: the same 1.0 mS/cm solution shows up as ~700 PPM. That's why two growers with different meters can "disagree" about the strength of a mix — the solution is the same, only the scale changes.
In practice: which number to follow
If your fertilizer chart gives the recommendation in EC (mS/cm), follow the EC — it's the meter's direct reading and doesn't depend on any scale. If you only have a PPM recommendation, check which scale your meter uses (manufacturer's manual) before comparing — converting on the wrong scale can leave your mix up to 40% stronger or weaker than you think.
Quick conversion (reference)
The "500" scale is the most common — use it as a starting point if your meter's manual doesn't specify the scale.
want to mix your feed and see the estimated EC right away?
The GrowerHelper app's NPK/EC calculator adds up your fertilizer formula and water volume, and shows the resulting N, P, K in mg/L and the estimated EC — straight from the fertilizer library you've already set up. All offline, no signup.