mg/l to ppm Converter
In water, 25 mg/L is 25 ppm, but in a heavier liquid the same mg/L means fewer ppm.
Quick answer: Divide the mg/L by the density of the liquid in g/mL. For example, 25 mg/L at 1 g/mL is 25 ppm, 100 mg/L at 1.2 g/mL is 83.333 ppm and 500 mg/L at 0.8 g/mL is 625 ppm.
The mg/L to ppm formula
Parts per million equal milligrams per litre divided by the density in g/mL.
For plain water the density is about 1, so the two numbers match.
Take 25 mg/L at 1 g/mL. 25 ÷ 1 gives 25 ppm.
Take 100 mg/L at 1.2 g/mL. 100 ÷ 1.2 gives 83.333 ppm.
Why density matters
One ppm by mass is 1 mg in 1 kg of the mixture, which is the same as 1 mg/kg (Wikipedia: Parts-per notation). A litre of a liquid holds a mass that depends on its density.
In dilute water solutions a litre weighs about a kilogram, so mg/L and ppm are used as the same number (Penn State EARTH 111: Units of water chemistry).
How to convert mg/L to ppm step by step
- Read the concentration in mg/L.
- Find the density of the liquid in g/mL. Use 1 for dilute water.
- Divide the mg/L by the density.
- Read the answer in ppm, or divide by 10,000 for percent.
Example 1: 25 mg/L at 1 g/mL
- Start with 25 mg/L at 1 g/mL.
- 25 ÷ 1 = 25.
- The concentration is 25 ppm.
25 mg/L at 1 g/mL = 25 ppm
Example 2: 100 mg/L at 1.2 g/mL
- Start with 100 mg/L at 1.2 g/mL.
- 100 ÷ 1.2 = 83.333.
- The concentration is 83.333 ppm.
100 mg/L at 1.2 g/mL = 83.333 ppm
Example 3: 500 mg/L at 0.8 g/mL
- Start with 500 mg/L at 0.8 g/mL.
- 500 ÷ 0.8 = 625.
- The concentration is 625 ppm.
500 mg/L at 0.8 g/mL = 625 ppm
The three examples below use common sizes.
Each one shows the sum in full.
mg/L to ppm conversion table
| Concentration and density | Parts per million (ppm) | Percent by mass (%) |
|---|---|---|
| 1 mg/L at 1 g/mL | 1 ppm | 0.0001 percent |
| 5 mg/L at 1 g/mL | 5 ppm | 0.0005 percent |
| 10 mg/L at 1 g/mL | 10 ppm | 0.001 percent |
| 25 mg/L at 1 g/mL | 25 ppm | 0.0025 percent |
| 50 mg/L at 1 g/mL | 50 ppm | 0.005 percent |
| 100 mg/L at 1 g/mL | 100 ppm | 0.01 percent |
| 25 mg/L at 0.8 g/mL | 31.25 ppm | 0.003125 percent |
| 25 mg/L at 1.25 g/mL | 20 ppm | 0.002 percent |
| 100 mg/L at 0.8 g/mL | 125 ppm | 0.0125 percent |
| 100 mg/L at 1.2 g/mL | 83.333 ppm | 0.008333 percent |
| 500 mg/L at 0.8 g/mL | 625 ppm | 0.0625 percent |
| 500 mg/L at 1.5 g/mL | 333.33 ppm | 0.0333 percent |
| 1,000 mg/L at 1 g/mL | 1,000 ppm | 0.1 percent |
The highlighted row is the default of the calculator. The last column gives percent.
A quick mental shortcut for mg/L to ppm
For water, copy the number. 40 mg/L is 40 ppm.
For another liquid, divide by the density. 100 mg/L in a liquid of density 1.25 g/mL is 80 ppm.
When mg/L equals ppm
The two units match when the liquid has a density of 1 g/mL. Dilute water solutions come close enough for most work (Penn State EARTH 111: Units of water chemistry).
Once the liquid is much heavier or lighter than water, the match breaks down.
Heavier and lighter liquids
A liquid with a density of 1.25 g/mL weighs 1.25 kg per litre. So 100 mg/L spread through it is 80 mg in each kilogram, which is 80 ppm.
A liquid with a density of 0.8 g/mL weighs 0.8 kg per litre, so 100 mg/L is 125 ppm.
ppm by mass and ppm by volume
This page uses ppm by mass, which is mg of solute per kg of mixture. Some fields use ppm for gases by volume, and that is a different quantity (Wikipedia: Parts-per notation).
Always check which one a source means.
Quick conversion answers
| Conversion | Result |
|---|---|
| 25 mg/L at 1 g/mL | 25 ppm |
| 100 mg/L at 1.2 g/mL | 83.333 ppm |
| 500 mg/L at 0.8 g/mL | 625 ppm |
| 1,000 mg/L at 1 g/mL | 1,000 ppm |
Where this conversion is used
Water testers read a result in mg/L and report it in ppm.
Lab staff correct for density when the liquid is not close to water.
Common mistakes to avoid
- Assuming the units always match. They match only near a density of 1 g/mL.
- Multiplying by the density. You divide by it.
- Using density in kg/m3. The page expects g/mL, so 1,000 kg/m3 is 1.
- Mixing mass and volume ppm. This page is for ppm by mass.
Related converters
More concentrations and densities
2 mg/L at 1 g/mL is 2 ppm. 7.5 mg/L at 1 g/mL is 7.5 ppm. 15 mg/L at 1 g/mL is 15 ppm.
40 mg/L at 1 g/mL is 40 ppm. 60 mg/L at 0.8 g/mL is 75 ppm. 80 mg/L at 1.25 g/mL is 64 ppm.
120 mg/L at 1.2 g/mL is 100 ppm. 250 mg/L at 0.9 g/mL is 277.8 ppm. 750 mg/L at 1.5 g/mL is 500 ppm.
Doubling the first number
4 mg/L at 1 g/mL is 4 ppm. 15 mg/L at 1 g/mL is 15 ppm. 30 mg/L at 1 g/mL is 30 ppm.
80 mg/L at 1 g/mL is 80 ppm. 120 mg/L at 0.8 g/mL is 150 ppm. 160 mg/L at 1.25 g/mL is 128 ppm.
240 mg/L at 1.2 g/mL is 200 ppm. 500 mg/L at 0.9 g/mL is 555.6 ppm. 1,500 mg/L at 1.5 g/mL is 1,000 ppm.
The same mg/L at different densities
100 mg/L at 0.8 g/mL is 125 ppm. 100 mg/L at 0.9 g/mL is 111.1 ppm. 100 mg/L at 1 g/mL is 100 ppm.
100 mg/L at 1.1 g/mL is 90.91 ppm. 100 mg/L at 1.25 g/mL is 80 ppm. 100 mg/L at 1.5 g/mL is 66.67 ppm.
Frequently asked questions
How do I convert mg/L to ppm?
Divide the mg/L by the density of the liquid in g/mL.
Is 1 mg/L equal to 1 ppm?
In dilute water, yes. For other liquids it depends on the density.
How many ppm is 100 mg/L at 1.25 g/mL?
80 ppm.
What is 1 ppm in mass terms?
1 mg of solute in 1 kg of the mixture, which is 1 mg/kg.
How do I get percent from ppm?
Divide the ppm by 10,000.
Which density should I use for water?
Use 1 g/mL for dilute water.
Sources
- Wikipedia: Parts-per notation (en.wikipedia.org)
- Penn State EARTH 111: Units of water chemistry (courses.ems.psu.edu)
