Concentration Converter

All concentration conversions use g/L as the base unit. These conversions assume water-based (aqueous) solutions where 1 L of water weighs 1 kg.

Key conversions:

• 1 g/L = 1,000 mg/L
• 1 g/L = 1,000,000 µg/L
• 1 g/L = 1 kg/m³
• 1 g/L = 1,000 ppm (parts per million, in water)
• 1 g/L = 1,000,000 ppb (parts per billion, in water)

Note on ppm and ppb:

• For water: 1 mg/L = 1 ppm, 1 µg/L = 1 ppb
• This is because water density is approximately 1 kg/L

Common references:

• Drinking water chlorine: about 0.2–4 mg/L (0.2–4 ppm)
• Sea water salt: about 35 g/L (35,000 ppm)

Beyond the water assumption noted above, the conversion most people get wrong is between the percentage forms. Weight/volume (w/v) is grams per 100 mL, weight/weight (w/w) is grams per 100 grams, and volume/volume (v/v) is for mixing two liquids. They give different numbers for the same solution, and a label that just says “5%” rarely tells you which one it means. The percent field above is w/v, the form used in labs and on most medical solutions: 1% w/v is 10 g/L, so normal saline at 0.9% is 9 g/L, which is 9,000 ppm.

Molarity adds one more step, because it counts molecules rather than mass. Converting to or from molarity always needs the solute’s molar mass, so a 1 molar solution of a heavy compound holds far more grams per liter than a 1 molar solution of a light one. That’s why a chemist reaching for “0.1 M” and a technician measuring “10 g/L” can be describing completely different concentrations of the same substance unless they convert carefully.

Molarity (mol/L) = concentration (g/L) / molar mass (g/mol)

Fill in the molar mass, or pick a solute from the dropdown, and the molarity fields come alive. Sodium chloride is 58.44 g/mol, glucose 180.16, calcium carbonate 100.09. Take that saline again: 9 g/L divided by 58.44 gives 0.154 mol/L, which is why you will see it written as 154 millimolar on a blood chemistry panel. Same solution, three notations, and the only way between them is the molar mass.