| Convert between EC and PPM in seconds — with the right scale for your meter. Most online converters get this wrong because they assume one scale fits all. They don’t. A reading of EC 1.4 mS/cm could mean 700 PPM, 896 PPM, or 980 PPM depending on which meter you own. This tool fixes that.
Pick your meter brand below, enter your reading, and get accurate conversions instantly. Bookmark this page — you’ll use it every time you mix nutrients. |
| Why your EC and PPM readings disagreeIf you’ve ever followed a feeding chart that listed PPM values and ended up with sickly plants, the conversion scale is probably why. Electrical conductivity (EC) is the actual physical measurement — your meter sends a small current through the solution and measures resistance. PPM (parts per million, also called TDS or total dissolved solids) is calculated from EC using a multiplier. The problem is that there isn’t one universal multiplier.
Three different scales are in use around the world. The 500 scale (sometimes called NaCl scale) is standard on most US and UK meters including Hanna, Milwaukee, HM Digital, and the popular Truncheon. The 700 scale (442 or KCl scale) is dominant in Australia and parts of Europe — Bluelab and Eutech use this. Some older European meters use a 640 scale. The same nutrient solution will give you three different PPM readings on three different meters, even though the actual nutrient concentration hasn’t changed.
EC itself is the universal standard. When professional growers and research papers specify nutrient strength, they almost always use EC for exactly this reason. If your nutrient bottle gives instructions in PPM and doesn’t state the scale, assume 500 scale (the most common). Better yet, convert to EC using this tool and work in EC from there. |
| The formula (so you can check the maths)The conversion is straightforward once you know your scale:
PPM = EC (mS/cm) × scale factor
EC (mS/cm) = PPM ÷ scale factor
Worked example: You’re growing lettuce and your Bluelab meter reads 1.2 mS/cm. Bluelab uses the 700 scale, so PPM = 1.2 × 700 = 840 PPM. If your friend with a Hanna meter dipped the same reservoir, their meter would show 1.2 × 500 = 600 PPM. Same solution, different number. Both are correct for their respective scale.
This is also why you should never mix advice from different sources without checking units. A YouTube grower in Australia saying “feed at 1400 PPM” probably means 1400 on the 700 scale (EC 2.0), but a US grower saying the same thing means 1400 on the 500 scale (EC 2.8). That’s a 40% difference in actual nutrient strength — easily enough to burn your plants. |
| Frequently asked questionsWhich scale should I use?
Use whichever scale your meter uses — that’s not optional. Check your meter’s manual or look at the brand. If your readings are in mS/cm or μS/cm, you’re already working in EC and can skip conversions entirely. If they’re in PPM, find your brand in the dropdown above.Is EC more accurate than PPM?
EC is the direct measurement, so it’s inherently more reliable. PPM is always a derived estimate. For serious growing, work in EC and use PPM only when a feeding chart forces you to.
My meter shows μS/cm, not mS/cm — what do I do?
Divide by 1000. A reading of 1400 μS/cm equals 1.4 mS/cm. The converter above uses mS/cm because that’s the standard unit in hydroponics charts.
Why does my meter read different values morning vs evening?
Temperature affects conductivity — most meters have automatic temperature compensation, but cheaper ones don’t. Solution levels also concentrate as plants drink water (EC rises) or absorb nutrients faster than water (EC drops). Daily fluctuations of 0.1–0.3 mS/cm are normal.
Does this work for soil and coco coir, not just hydroponics?
The conversion maths is identical — EC is EC regardless of growing medium. Target ranges differ though, because soil and coco buffer nutrients differently. The crop ranges in the table above are for hydroponics specifically.
My tap water already reads 0.4 mS/cm — should I subtract that?
Yes. Your “true” nutrient EC is the final reading minus your starting water EC. If tap water is 0.4 and your final solution reads 1.6, you’ve added 1.2 EC of nutrients. This matters most for hard tap water — if yours is above 0.5, consider an RO filter for sensitive crops.
Can I use this for aquariums or pools?
The conversion formula works for any aqueous solution, but the crop reference ranges obviously don’t apply. For aquariums, target EC depends on the species you’re keeping. |
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