PPB Formula

Ultra-low concentration measurement

Definition

ppb = (mass_solute / mass_solution) × 10^9

For aqueous solutions, ppb ≈ μg/L when density ≈ 1 g/mL.

Example

Given: 3.0 μg solute in 1.5 L water.

Assuming ρ ≈ 1 g/mL, 1.5 L ≈ 1500 g solution.

ppb = (3.0 μg / 1500 g) × 10^9 = (3.0 × 10⁻⁶ g / 1500 g) × 10^9 ≈ 2000 ppb

Answer: ≈ 2000 ppb

Notes

  • For gases, ppb often refers to volume ratio.
  • Check density and units carefully; ppb is very sensitive to unit mistakes.