A lead concentration in tap water of 15 ppb is equal to what concentration in ppm?

1. ppm multiplies the mass ratio by 10^6 and ppb multiplies it by 10^9. 2. Comparing the two shows that 1 ppm equals 10^3 ppb. 3. So convert by dividing: 15 ppb x 1 ppm / 10^3 ppb. 4. The result is 0.015 ppm. 5. Multiplying by 1000 instead of dividing gives 15000 ppm, which would be an enormous concentration rather than a trace one. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.4 Other Units for Solution Concentrations_