EC / PPM Converter

Convert between EC (mS/cm), µS/cm, PPM-500 (NaCl scale, US), and PPM-700 (KCl / 442 / European scale). Live-update across all four.

Convert

EC (mS/cm) Millisiemens per cm; standard in EU/Aus

µS/cm EC × 1000; sometimes used for low EC water

PPM-500 (NaCl scale) US default; EC × 500

PPM-700 (KCl / 442 scale) European default; EC × 700

Crop and stage reference

Crop — Pick to see target ranges — Lettuce / leafy greens Herbs (basil, etc.) Tomato Pepper Cucumber Strawberry Cannabis Microgreens

Why three different PPM scales exist

EC is the actual measurement — electrical conductivity of the solution. PPM is a derived approximation: "if all the dissolved solids were one specific compound, this is what they'd weigh." Different compounds have different conductivity per gram, so the conversion factor depends on what calibration standard the meter assumes.

Scale	Conversion	Where used	Calibration standard
PPM-500 (NaCl scale)	EC × 500	US, China, Korea	Sodium chloride
PPM-700 (KCl / 442)	EC × 700	EU, Australia	Potassium chloride or "442 mix"
PPM-650 (uncommon)	EC × 650	Some hydroponic suppliers	Mixed standard
EC (µS/cm)	direct	Universal lab standard	Calibration solutions

Important: Don't compare PPM numbers across scales without converting. A "1200 ppm recipe" written in PPM-500 = 2.4 EC = 1680 ppm on the PPM-700 scale. The same recipe — but the labels look 40% different.

Crop EC reference (in mS/cm)

Crop	Veg / early	Production / mid	Late / fruiting
Lettuce / leafy greens	0.8-1.2	1.2-1.6	1.6-1.8
Basil / soft herbs	0.8-1.2	1.2-1.8	1.8-2.0
Tomato	1.5-2.0	2.5-3.5	3.5-4.5
Pepper	1.5-2.0	2.0-3.0	3.0-3.5
Cucumber	1.8-2.2	2.2-2.8	2.8-3.2
Strawberry	1.0-1.4	1.4-1.8	1.8-2.0
Cannabis	1.0-1.5	1.5-2.2	2.2-2.6
Microgreens	0.5-0.8	0.8-1.2	—

Practical guidance

• Run lower in heat. Plants transpire more water than they take up nutrients in hot conditions. EC creeps up over the day; bring fresh feed in lower than usual to compensate.
• Watch the run-off, not the feed. The EC the plant sees is the run-off / drain EC, not what came out of your tank. If runoff EC is 50%+ above feed EC, salts are accumulating in substrate; flush.
• Cold water has lower EC reading at same nutrient content. Most modern meters auto-compensate for temperature; older ones don't. Calibrate at your typical solution temperature.
• EC measures total dissolved salts, not which ones. A solution can have correct EC and still be missing critical elements. Plant tissue testing is the next-level confirmation.

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