About the PPM Converter
Parts per million, billion and trillion describe very small shares of a whole, such as chlorine in pool water, lead in drinking water or a nutrient in soil. This page converts between percent, per mille, ppm, ppb, ppt, milligrams or micrograms per kilogram, and milligrams or micrograms per litre. Two extra boxes answer the questions people really ask: how much of a substance is in a sample at a given ppm, and what share a measured part is of a whole. The mg/L and µg/L units equal ppm and ppb only in dilute water, which weighs about one kilogram per litre. For oil, air or strong solutions the two are not the same. Air gas readings in ppm are by volume and are not converted to mass here.
Updated September 2026
How to use the PPM Converter
- 1Type the value and choose the unit you have in From and the unit you want in To.
- 2Read the big answer, the plain-language '1 part in N' line, and the list of every unit.
- 3To find the amount in a sample, enter the sample size and its unit in How much is in a sample?
- 4To find a share, type a part and a whole in the same unit in What share is a part?
- 5Press Copy result to take the plain number.
Reading parts-per units
A part-per unit states a share of a whole. Percent is parts per hundred, per mille parts per thousand, ppm parts per million, ppb parts per billion and ppt parts per trillion. The whole can be measured by mass, volume or number of molecules, and the label should say which; this tool assumes mass, which is how water, food and soil results are usually reported.
Switching between the units is only a matter of moving the decimal point, but it is easy to be off by a factor of 10 or 1,000 when you do it in your head. The list of all units under the answer lets you check the value in the form you need.
Common uses
Parts-per numbers show up wherever tiny amounts matter, and each field favours its own unit.
- Water quality: lead and arsenic in ppb or µg/L, hardness and chlorine in ppm or mg/L
- Pools and aquariums: chlorine, salt and nitrate in ppm
- Soil and plants: nutrient levels in mg/kg
- Food: additives, contaminants and salt in ppm or percent
- Air and industry: trace gases in ppm by volume
Working out an amount
If a label says a drink has 5 ppm of a preservative and you have 2 litres, the substance weighs about 10 milligrams, since 1 ppm of water is 1 milligram per litre. Choose ppm, type 5, and enter a sample of 2,000 with the unit g: the answer is 0.01 g, which is 10 milligrams.
For related conversions, the Percentage Calculator handles everyday percent questions, and the Scientific Notation Converter writes very small shares such as 1e-9 in a cleaner form. For other units use the Unit Converter, and for kitchen amounts the Cooking Measurement Converter helps.
Features
- Percent, per mille, ppm, ppb, ppt, mg/kg, µg/kg, mg/L and µg/L
- A plain '1 part in N' reading for every result
- All units listed together under the main answer
- Sample calculator: grams, kilograms or litres of substance at a given ppm
- Share calculator: a part and a whole turned into percent, ppm and ppb
- Honest note that mg/L equals ppm only in dilute water
- Clear messages for negative, empty or huge input
- Runs in your browser with nothing sent anywhere
Frequently asked questions
How do I convert ppm to percent?
Divide the ppm by 10,000. So 25 ppm is 0.0025 percent and 10,000 ppm is exactly 1 percent. To go from percent to ppm, multiply by 10,000, which is how 0.5 percent becomes 5,000 ppm.
What is the difference between ppm, ppb and ppt?
They step down by a factor of 1,000 each time. One ppm is one part in a million, one ppb is one part in a billion and one ppt is one part in a trillion. So 1 ppm equals 1,000 ppb, which equals 1,000,000 ppt.
Is 1 ppm the same as 1 mg/L?
Only in dilute water. A litre of water weighs about a kilogram, and a milligram per kilogram is one ppm, so the two match. In a liquid that is lighter or heavier than water, such as oil or brine, the litre weighs a different amount and the numbers drift apart.
How many grams are in a sample at a given ppm?
Multiply the sample size by the ppm and divide by one million. For 50 ppm in 2,000 grams you get 0.1 grams. The sample box above does this with your numbers and keeps the unit you choose.
Does the converter work for gases in air?
Not directly. Gas concentrations in ppm are usually by volume, and turning them into milligrams per cubic metre needs the molar mass of the gas, the temperature and the pressure. This page handles shares by mass and dilute water only.
What does 1 part in a million look like?
One ppm is about one drop in a 50-litre barrel or one second in roughly eleven and a half days. The page shows a 1 part in N line under each result so you can picture how small the share is.
What is a per mille?
A per mille, written ‰, means parts per thousand. It is used for salinity and alcohol, where 35‰ seawater has 35 grams of salt per kilogram. One per mille is 0.1 percent and 1,000 ppm.