PPM Concentration Calculator
Work out parts per million from a mass of solute in a solution, convert between ppm, ppb, percent, mg/L, µg/L, g/L, grains per gallon and molarity with a density correction, or convert gas ppm to mg/m³ at any temperature and pressure.
How it works
ppm (by mass) = mg of solute ÷ kg of solution = mass fraction × 10⁶ · mg/L = ppm × density (g/mL) · % = ppm ÷ 10,000 · ppb = ppm × 1,000 · molarity (mol/L) = mg/L ÷ (molar mass × 1,000) · 1 gpg = 17.12 mg/L · gas: mg/m³ = ppm × molar mass ÷ molar volume, molar volume = 0.08206 × T(K) ÷ P(atm) L/mol (24.45 at 25 °C, 1 atm)
Parts per million expresses very dilute concentrations — one part solute in a million parts of the whole. For liquids and solids it is a mass ratio: milligrams of solute per kilogram of solution. Because a litre of dilute water solution weighs about one kilogram, milligrams per litre equal ppm for drinking water, pool water and most lab solutions; for denser liquids such as seawater (about 1.025 g/mL) or brines, mg/L = ppm × density, which the density option handles. Dividing ppm by 10,000 gives the mass percentage, and multiplying by 1,000 gives parts per billion. With the solute’s formula or molar mass, mg/L converts to molarity (mol/L). For gases in air, ppm is by volume (moles of gas per million moles of air) and converts to mg/m³ with the gas’s molar mass and the molar volume from the ideal gas law — 24.45 L/mol at 25 °C and 1 atm, the basis of most workplace exposure limits.
Worked example
5 mg of a substance dissolved in 1 L of water is 5 ÷ 1 = 5 ppm, equal to 5 mg/L, 5,000 ppb or 0.0005%. If the substance is sodium chloride (NaCl, 58.44 g/mol), that is 5 ÷ (58.44 × 1,000) = 0.0000856 mol/L. In seawater (1.025 g/mL), 5 mg/L would be 5 ÷ 1.025 = 4.88 ppm by mass. For a gas, 50 ppm of carbon monoxide (28.01 g/mol) at 25 °C and 1 atm is 50 × 28.01 ÷ 24.47 = 57.2 mg/m³.
Sources: Parts-per notation — Wikipedia · NIOSH Pocket Guide to Chemical Hazards — conversion factors at 25 °C · NIST — CODATA molar gas constant
Frequently asked questions
Why does mg/L equal ppm for water?
One litre of water has a mass of about one million milligrams (1 kg). So milligrams of solute per litre is milligrams per million milligrams — parts per million by mass. For liquids denser or lighter than water, multiply ppm by the density in g/mL to get mg/L.
What is ppm used for?
Trace concentrations: contaminants in drinking water, dissolved oxygen, chlorine in pools, nutrients in hydroponics, or pollutants in air. At these levels percent would be an unwieldy string of zeros.
How do I convert ppm to percent?
Divide by 10,000. So 10,000 ppm is 1%, and 5 ppm is 0.0005%. The calculator shows the percentage, ppb, mg/L and the other units automatically.
How do I convert ppm of a gas to mg/m³?
Multiply ppm by the gas’s molar mass and divide by the molar volume: 24.45 L/mol at 25 °C and 1 atm. 50 ppm of carbon monoxide is about 50 × 28.01 ÷ 24.45 = 57 mg/m³. Choose “Gas in air” to do it at any temperature and pressure.
How do I turn ppm into molarity?
For a water solution, mg/L ≈ ppm; divide by the molar mass × 1,000. 200 ppm of NaOH (40.00 g/mol) is 200 ÷ 40,000 = 0.005 mol/L. Enter the formula in More options and the calculator works out the molar mass for you.
What is the difference between ppm and ppb?
ppb is parts per billion, a thousand times smaller: 1 ppm = 1,000 ppb. It is used for still more dilute traces, such as lead or arsenic in drinking water.
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