EC ↔ PPM Converter

How to Use the EC ↔ PPM Converter

• Find which scale your meter uses — it is in the manual or the setup menu, and the three options are listed on the dropdown.
• Type your EC reading to see the ppm equivalent on that scale.
• Or type a ppm reading to recover the EC, which is the number most nutrient charts prefer.
• Select your crop to check the result against its typical working EC range.
• When following a recipe written on another scale, convert to your meter's scale before dosing — not after.

The EC ↔ PPM Formula, Explained

Worked Example: The Chart Says 1,400 ppm

• Your reservoir target per the nutrient bottle chart: 1,400 ppm, scale unstated.
• Your meter converts on the 500 scale, and a friend's budget probe reads 700.
• Reading 1,400 as a 500-scale number: EC = 1,400 ÷ 500 = 2.8 mS/cm.
• Dosed to 2.8 EC, the 700-scale probe will display 1,960 ppm — alarming only if you believed its display units.
• The reverse trap: targeting 1,400 on a 700 meter gives EC 2.0, and your 500-scale meter reports a starving 1,000 ppm.
• Translate once, then never dose from ppm again: write the EC and the scale on the reservoir lid.
• Cross-check against the crop range: tomatoes run 2.0–3.5 EC, so both readings are agronomically plausible — only the intent differs.

The Three Scales at a Glance

Key Terms

EC (electrical conductivity)

How strongly a solution carries current, in mS/cm — the direct proxy for dissolved nutrient ions.

TDS

Total dissolved solids estimated from EC via a ppm scale; ppm 500 and ppm 700 are both TDS claims.

ppm scale

The conversion constant (442/500/700) that turns EC into a weight-like number — a calibration assumption, not a measurement.

Working EC

The feed strength a crop performs at, distinct from the drainage/leachate EC that reveals salt build-up.

Calibration solution

The buffered standard (usually 1.0 or 1.414 mS/cm or 3.5) used to keep an EC meter honest.

What This Means in a Real Reservoir

• Standardize on EC and stop reading ppm outright — it is the measurement; ppm is the translation, and translations introduce arguments.
• EC rises as plants drink water faster than nutrients, so a climbing number midweek usually means the level dropped: top up with pH-adjusted water, then re-read before dosing more.
• Temperature compensates the reading: cold solutions conduct less, so a meter without ATC under-reports at 15 °C by roughly ten percent per degree gap.
• Feed charts and crop ranges that name a number without a scale are legacy — most modern extension and commercial hydro guidance has converged on EC for exactly this reason.
• Drainage EC above roughly 1.5× the feed EC says salts are banking in the medium; flush and step the feed down before tip burn shows up.

Common Mistakes & Fixes

• Treating a 700-scale TDS pen and a 500-scale EC meter as interchangeable readers of the same number — they are not, and the 40% gap is the whole problem.
• Chasing a ppm target from an old chart with a new meter, then 'correcting' with nutrients until the recipe is a double dose of everything.
• Calibrating with expired or contaminated solution, which makes a wrong scale look even wronger — fresh standards first, then arguments.
• Reading a cold reservoir straight from the chiller: let the sample reach air temperature or trust the ATC spec, not the display.
• Adding more Cal-Mag to raise a ppm number the plants never asked for — check the crop range output before dosing anything.

When to Use This Converter (and When Not To)

EC ↔ PPM Converter: Frequently Asked Questions