About the PPM Converter
This PPM converter translates a concentration between parts per million, parts per billion, parts per trillion, percent, mg/L, µg/L, g/L and mg/kg. Enter a value in any of those units and see every other form at once — for example 250 ppm is 0.025%, 250,000 ppb and, in water, 250 mg/L.
It is designed for water testing (TDS, chlorine, nitrate, hardness), pool and aquarium care, hydroponic nutrient mixing, lab work and environmental reports that quote limits in different units. An optional molecular weight turns a gas reading in ppm by volume into mg/m³, the unit used in many workplace exposure limits.
The key assumption is density. For dilute water solutions, one litre weighs about one kilogram, so 1 ppm = 1 mg/L. For brines, seawater or other liquids, enter the actual density in g/mL and the mg/L figures are adjusted: ppm by mass = (mg/L) ÷ density. The gas conversion assumes 25 °C and 1 atm (24.45 L/mol).
With the default inputs, the converted concentration is 250. Change any value above to recalculate instantly.
How to use the ppm converter
- 1Enter the concentration value.
- 2Choose the unit it is expressed in and the unit you want.
- 3For liquids other than fresh water, enter the solution density.
- 4For a gas reading, enter the molecular weight to see mg/m³.
- 5Read the converted value and the full list of equivalents.
Formula and method
Parts per million, billion and trillion are simply ratios multiplied by 10^6, 10^9 and 10^12, and percent is the ratio × 100. So 1% = 10,000 ppm and 1 ppm = 1,000 ppb. The calculator turns your input into a plain mass fraction, then expresses that fraction in the unit you want.
Mass-per-volume units need the solution density ρ in kg/L (numerically equal to g/mL): 1 mg/L equals 1 ÷ ρ mg per kg of solution, i.e. ppm by mass. For dilute water solutions ρ ≈ 1, which is why ppm and mg/L are used interchangeably. For gases, ppm usually means parts per million by volume; multiplying by the molecular weight and dividing by the molar volume (24.45 L/mol at 25 °C and 1 atm) gives mg/m³.
- ρ
- Solution density in g/mL (kg/L)
- MW
- Molecular weight of the gas in g/mol
- ppmv
- Parts per million by volume (gases)
Worked examples
250 ppm in water to mg/L
With a density of 1 g/mL, 1 ppm = 1 mg/L, so 250 ppm is 250 mg/L. It is also 250 ÷ 10,000 = 0.025% or 250 × 1,000 = 250,000 ppb.
0.5% solution to ppm
One percent is 10,000 ppm, so 0.5% × 10,000 = 5,000 ppm — about 5,000 mg/L in a water-based solution.
Seawater salinity from mg/L
Seawater holds about 35,000 mg of salt per litre, but a litre weighs 1.025 kg, so the mass ratio is 35,000 ÷ 1.025 = 34,146 ppm (about 3.4%).
Carbon monoxide alarm reading
A 50 ppm CO reading is 50,000 ppb. As a gas at 25 °C it is 50 × 28.01 ÷ 24.45 = 57.3 mg/m³.
Frequently asked questions
Is ppm the same as mg/L?+
For dilute solutions in water, yes: a litre of water weighs about 1 kg, so 1 mg/L ≈ 1 mg/kg = 1 ppm. For dense liquids like brine or seawater, divide mg/L by the density in g/mL to get true ppm by mass.
How do I convert ppm to percent?+
Divide ppm by 10,000. For example 2,500 ppm = 0.25% and 10,000 ppm = 1%. To go from percent to ppm, multiply by 10,000.
How many ppb are in a ppm?+
One ppm equals 1,000 ppb. So 0.015 ppm of lead is 15 ppb, and 10 ppb of arsenic is 0.01 ppm — the same number in a different scale.
How do I convert ppm to mg/m³ for a gas?+
Use mg/m³ = ppm × molecular weight ÷ 24.45 at 25 °C and 1 atm. For CO₂ (44.01 g/mol), 1,000 ppm is about 1,800 mg/m³. Use 22.41 instead of 24.45 for 0 °C.
Does ppt mean parts per thousand or parts per trillion?+
Both usages exist. In trace-contaminant work (for example PFAS in drinking water) ppt means parts per trillion, 10^−12. In oceanography and aquaculture, salinity in ppt (‰) means parts per thousand, 10^−3 — 35 ppt seawater is 35,000 ppm. This tool uses ppt for parts per trillion.
What does TDS in ppm mean?+
Total dissolved solids meters report the dissolved minerals in ppm, which for drinking water is effectively mg/L. Many meters estimate TDS from electrical conductivity using a conversion factor of about 0.5–0.7.