Concentration converter
Convert between ppm, ppb, percent and mg per liter, the units of water tests, air quality and laboratory solutions.
That's 20× as concentrated as the drink-drive limit, while salt in seawater is 3.5× stronger. In a liter of water that is about 10,000 mg.
What it means
How strong is that?
For dilute water solutions 1 ppm equals 1 mg/L, because a liter of water weighs a kilogram. For air and other liquids that shortcut does not hold.
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Three things worth knowing
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1% is 10,000 ppm
Percent to ppm is four decimal places. Pool chlorine at 2 ppm is 0.0002%, and air at 420 ppm CO₂ is 0.042%.
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Why labs left percent behind
Trace contaminants would be written as 0.000001%, which invites mistakes. Parts per million keeps the numbers readable and the decimal point safe.
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ppm by weight or by volume?
Air quality quotes ppm by volume, water by weight. The same number can mean different amounts, so always check which basis a figure uses.
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Background
About concentration units
Percent is parts per hundred, ppm parts per million, ppb parts per billion. Water labs also use mg/L, which matches ppm exactly for dilute solutions.