PPM ↔ mg/L Converter
ppmtomgl.com • Concentration units

PPM to mg/L Converter

Real-time ppm ↔ mg/L conversion with optional molar concentration, built for water quality and lab work.

Decimals:
2
▾

Choose whether you want to start from ppm or from mg/L.

ppm

The number you want to convert (source unit changes with the direction).

▾
g/mL

For dilute aqueous solutions you can keep water selected (≈1.000 g/mL).

g/mol

Enter the solute molar mass (e.g., NaCl ≈ 58.44 g/mol) to see molar concentration.

Did we solve your problem today?

What are PPM and mg/L?

PPM (parts per million) is a dimensionless ratio that typically means milligrams of solute per kilogram of solution (mg/kg). It is widely used in water quality, environmental analysis, and chemistry to express very small concentrations.

mg/L (milligrams per liter) is a mass-per-volume concentration unit. It tells you how many milligrams of solute are present in one liter of solution. Because PPM is mass-based and mg/L is volume-based, they are only numerically identical when the solution density is close to 1 kg/L.

Converting between PPM and mg/L

The general link between PPM and mg/L uses the solution density ρ in kg/L:

  • mg/L = ppm × ρ (kg/L)
  • ppm = mg/L ÷ ρ (kg/L)

For dilute aqueous solutions where ρ ≈ 1 kg/L, the common rule-of-thumb 1 ppm ≈ 1 mg/L works well. For denser or lighter solutions (such as seawater or some chemicals), you should use the exact relation with the correct density.

Special case: water

At room temperature, the density of pure water is very close to 1 kg/L. That means:

  • 1 ppm in water ≈ 1 mg/L
  • 10 ppm in water ≈ 10 mg/L
  • 100 ppm in water ≈ 100 mg/L

This is why most water quality charts treat ppm and mg/L as interchangeable. This converter defaults to water but allows you to choose seawater or enter your own density if you need more precise results.

Calculating the molar concentration

If you know the molar mass \( M \) of your solute (in g/mol), you can convert from mg/L to molar concentration (mol/L) in two simple steps:

  1. Convert mg/L to g/L: g/L = (mg/L) ÷ 1000.
  2. Divide by molar mass: mol/L = (g/L) ÷ M.

Combined into one formula:

mol/L = (mg/L) ÷ (1000 × M)

The calculator uses this expression internally: when you fill in the solute molar mass, it computes both the ppm ↔ mg/L conversion and the corresponding molar concentration in real time.

FAQs

How do I convert PPM to milligrams per liter?
Multiply PPM by the solution density in kg/L to get mg/L. For most water-based work, density is very close to 1 kg/L, so 1 ppm ≈ 1 mg/L. In this tool, set the direction to “PPM → mg/L”, choose a density preset (or enter a custom value), type your ppm value, and the mg/L result will update instantly.
How do I calculate PPM and milligrams per liter for water?
For water, 1 L has a mass of roughly 1 kg. That’s why 1 ppm usually corresponds to about 1 mg/L. To go from ppm to mg/L in water, use mg/L ≈ ppm. To go from mg/L to ppm, use ppm ≈ mg/L. Simply keep “Water (~1.000 g/mL)” selected in the density dropdown and enter your value in the calculator.
Is PPM the same as mg/L?
Not exactly. PPM is a mass ratio (mg/kg), while mg/L is mass per volume. However, for dilute aqueous solutions where density is close to 1 kg/L, ppm and mg/L are numerically almost identical, which is why many references treat them as equivalent. When density is not 1 kg/L, use the density-based conversion to switch between the two.
What is 50 PPM in mg/L?
In water at typical conditions, 50 ppm is approximately 50 mg/L. With the exact relation mg/L = ppm × density (kg/L): for density 1.00 kg/L, 50 ppm → 50 mg/L; for a slightly denser solution with density 1.02 kg/L, 50 ppm → about 51 mg/L.
How do you convert ppm to mg/L?
Use mg/L = ppm × density (kg/L). If you are working with clean water, take density ≈ 1 kg/L, so ppm and mg/L are essentially the same. In the calculator, just choose the “PPM → mg/L” direction, select your density, and type the ppm value to see the mg/L result instantly.
Is 1 mg/L equal to 1 ppm?
1 mg/L equals 1 ppm only if the solution density is exactly 1 kg/L. For water and many dilute aqueous solutions this is a good approximation, so 1 mg/L ≈ 1 ppm. If the density differs significantly from 1, you should convert using ppm = mg/L ÷ density (kg/L).
Is 1 ppm equal to 1 mg?
No. PPM is a ratio, not an absolute mass. 1 ppm means one part solute per one million parts solution by mass. To get a mass in milligrams you must multiply by the total mass of solution. In 1 liter of water (mass ≈ 1 kg), 1 ppm corresponds to about 1 mg of solute.
What is 100 ppm in 1 liter?
In 1 liter of water, 100 ppm corresponds to roughly 100 mg of solute, assuming density ≈ 1 kg/L. More generally, mg per liter ≈ ppm × density (kg/L), so for water 100 ppm ≈ 100 mg/L.