Introduction
Concentration is how much solute per solvent. Chemistry uses molarity (mol/L); food labels use percent or mg per serving; medicine uses mg/dL or mmol/L; pollution uses parts per million (ppm) or parts per billion (ppb). This calculator handles the common numeric conversions.
Why concentration units exist and how they diverged
Concentration units aren't always inter-convertible without knowing the molecular weight of the solute. A 1 M (molar) glucose solution is 180 g/L (glucose molecular weight 180); 1 M sodium chloride is 58 g/L. Percent by weight, percent by volume, and percent mass/volume are three different things for dense or volatile solutes.
How to convert concentration
Parts per million (ppm) ≈ mg/L for dilute aqueous solutions. Percent by mass = g solute per 100 g solution. To convert % to ppm: multiply by 10,000. A 0.1% solution is 1,000 ppm.
Units supported by this concentration calculator
- mg/L (= ppm by mass in water)
- ppm (mass)
- ppb
- ppt (parts per trillion)
- Percent (%)
- g/L
- g/mL
- µg/L
- g/kg (for water, ~g/L)
- mg/kg (= ppm by mass)
Common concentration conversion mistakes
- ppm vs mg/L. Approximately equal for water (density 1); different for other solvents. A 1 ppm Hg in mercury (density 13.5) is 13.5 mg/L, not 1 mg/L.
- Percent by mass vs volume. 10% ethanol by volume ≠ 10% by mass (ethanol density 0.789).
- Molar vs molal. Molar (M) is mol per liter of solution; molal (m) is mol per kg of solvent. Different for concentrated or hot solutions.
- mg/dL vs mmol/L in medicine. Blood glucose in US: mg/dL (normal ~90). In most other countries: mmol/L (normal ~5). 90 mg/dL = 5 mmol/L because glucose molecular weight is 180 and 180 mg/dL = 10 mmol/L by arithmetic.
Real-world concentration examples
- Seawater: ~35,000 ppm salt (3.5% salinity).
- Drinking water sodium (US EPA): <20 ppm recommended.
- Blood glucose (normal fasting): 70-100 mg/dL = 3.9-5.6 mmol/L.
- CO₂ in atmosphere (2026): ~425 ppm.
- Lead in drinking water (EPA action level): 15 ppb.
- IV saline: 0.9% w/v (9 g/L NaCl, isotonic).
- Vinegar: 5-8% acetic acid.
- Rubbing alcohol: 70% isopropanol.
Tips for accurate concentration conversion
- For water testing, ppm and mg/L are interchangeable in practice.
- For medical lab results, know the unit — mg/dL vs mmol/L differ by molecular weight.
- For chemistry, always label units and molarity unambiguously.
Related: Density Converter · Cooking Weight Converter · SI Prefix Converter.