Pharmaceutical Chemistry

PPM & PPB Calculator

Works out a concentration in ppm, ppb, mg/L or molarity from a weighed mass, or converts between concentration units.

Concentration result

1000.0000ppm

Very high concentration

Inputs

Mass of solid

Mass weighed out, in grams (1 mg = 0.001 g).

Final solution volume

Total volume after making up, in litres (250 mL = 0.25 L).

Convert to

The unit the result is reported in.

Try an example

Working

The numbers you entered, plugged into the formula.

mg/L = (1 g × 1000) / 1 L = 1000.0000

ppm = 1000.0000 (aqueous: 1 mg/L ≈ 1 ppm) = 1000.0000

In scientific notation1.000e+3ppm

To 4 significant digits1000ppm

Common concentration ranges

Real-world values in ppm, for a sense of scale.

Description	Regulation	Value
Drinking Water (Pb)	EPA limit	0.015ppm
Sea Water (Salt)	Average	35000ppm
Blood Alcohol (0.08%)	Legal limit	800ppm
Vitamin C in Orange	Typical	500ppm
Air (CO₂)	Current average	420ppm
Gold in Seawater	Trace	0.000004ppm

Mass to Concentration

Solid: mg/L = (mass in g × 1000) / volume in L

Liquid: mg/L = (volume in mL × density × 1000) / volume in L

The mg/L figure is then reported in the chosen unit: ppb and μg/L × 1000, ppt and ng/L × 1,000,000, g/L ÷ 1000, and mol/L = mg/L ÷ 1000 ÷ MW.

Key relationships

For water solutions: 1 ppm ≈ 1 mg/L

1 ppm = 1000 ppb = 1,000,000 ppt

1 mg/L = 1000 μg/L = 1,000,000 ng/L

Molarity to ppm: ppm = M × MW × 1000

For other solvents: ppm = (mg/L) ÷ density

Unit Conversion

result = value × factor(from) ÷ factor(to)

Factors: ppm and mg/L 10⁻⁶, ppb and μg/L 10⁻⁹, ppt and ng/L 10⁻¹², g/L 10⁻³, mol/L and M 1. Note: these conversions assume dilute aqueous solutions at room temperature.

Guide: Dilution and Concentration CalculationsThe concept in full, with practice questions.

References

International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (the 'Gold Book'). Source
Bureau International des Poids et Mesures. The International System of Units (SI Brochure). 9th ed. Sèvres: BIPM; 2019. Source

Common questions

Only for dilute water solutions, where a litre weighs about a kilogram. ppm is a mass ratio (mg per kg); mg/L is mass per volume. For a solvent with a different density, divide mg/L by the density in g/mL to get ppm.

Mass of a solid in grams, volume of a liquid solute in millilitres, and the final solution volume in litres. Convert first: 5 mg is 0.005 g, and 250 mL is 0.25 L.

Results below 0.001 are shown in scientific notation: 2.500e-4 means 2.500 × 10⁻⁴. The Working section also gives every result in scientific notation and to 4 significant digits.

Divide mg/L by 1000 to get g/L, then by the molecular weight to get mol/L. Use Mass to Concentration with 'Convert to' set to M — Unit Conversion does not use the molecular weight.

About ppm and ppb

Parts per million (ppm) and parts per billion (ppb) describe very small amounts of one substance in another: 1 ppm is one part in 10⁶, 1 ppb one part in 10⁹. In dilute water solutions, where 1 L weighs about 1 kg, 1 ppm is effectively 1 mg/L and 1 ppb is 1 μg/L.

Use it when

Reporting trace impurities, heavy metals or residual solvents

Preparing a dilute standard from a weighed solid or measured liquid

Comparing a result with a limit given in a different unit

Quick conversions

1 ppm =

1000 ppb

1 ppb =

1000 ppt

1 mg/L =

1000 μg/L

1 M =

MW g/L

Read with care

These conversions assume dilute aqueous solutions at room temperature

ppm is by mass; mg/L is by volume — they are equal only when the solution's density is about 1 g/mL

Unit Conversion mode uses fixed factors and does not use molecular weight for molar units

Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy