PPM Converter

Convert between ppm, ppb, percent and mg/L for water, and between ppm and mg/m³ for gases.

In	Water / dilute solution
Value	250
Unit	ppm

Value

Unit

Parts per million

250

= 250 mg/L ≈ mg/kg, 250,000 ppb, 0.025%. (mg/L equals ppm for water and dilute solutions with density ≈ 1 kg/L.)

ppm (mg/L): 250
ppb (µg/L): 250,000
Percent: 0.025%
g per m³ of water: 250

About the PPM Converter

Parts per million is a ratio: 1 ppm is one part in a million. In water, 1 mg of a substance per litre is 1 ppm by mass, because a litre of water weighs a kilogram. For gases, ppm is by volume, so converting to mg/m³ depends on the molar mass and temperature: at 25 °C and 1 atm a mole of gas takes up 24.45 L.

The formula

1% = 10,000 ppm; 1 ppm = 1,000 ppb; mg/m³ = ppm × M ÷ 24.45 (25 °C)

Worked example

Example: Parts per million = 280

Inputs: In: Water / dilute solution; Value: 280; Unit: ppm.
Formula: 1% = 10,000 ppm; 1 ppm = 1,000 ppb; mg/m³ = ppm × M ÷ 24.45 (25 °C)
Result: Parts per million = 280
ppm (mg/L): 280
ppb (µg/L): 280,000
Percent: 0.028%

Questions people ask

Is TDS in ppm the same as mg/L?

Yes, for water.

What's a safe CO₂ level indoors?

Outdoor air is about 420 ppm; indoor levels below 1,000 ppm are commonly recommended.