PPM to mg/L Converter

Why ppm and mg/L are the same number in pool water

Parts per million (ppm) is a ratio -- one part of something per million parts of the whole -- while milligrams per liter (mg/L) is a concentration by mass and volume. The two only line up exactly when the solution's density is very close to 1 kilogram per liter, which is true for pool, spa and drinking water at normal temperatures. That's why every US pool test kit and every European or Australian pool test kit report the identical number, just under a different unit label.

This matters in practice because test strips and digital testers sold outside the US often print results in mg/L instead of ppm, and imported chemical labels sometimes do the same. If you're comparing a US-made chlorine test kit (in ppm) against an imported one (in mg/L), or reading a European water-treatment spec sheet, you can treat the numbers as directly interchangeable for chlorine, salt, cyanuric acid, alkalinity and pH-adjacent readings.

The one place this stops being exact is a highly concentrated or non-aqueous solution -- a full-strength chemical concentrate rather than diluted pool water -- where density shifts enough that ppm and mg/L drift apart. For anything you'd actually test with a pool kit, the 1:1 relationship holds.

Run your ppm reading straight into the pool chemical calculator or the pool salt calculator once you know it -- both expect ppm, which now you know is the same as mg/L.

Where these numbers come from

The formulas and default values in this calculator are based on:

• standard water-chemistry reference (ppm and mg/L are equivalent for solutions with density approximately 1 kg/L, which includes pool, spa and drinking water at normal temperatures)

These are planning estimates. Test your actual water, follow product labels, and check your equipment manufacturer's guidance before you buy or dose chemicals.