ng/g to PPB Converter
Common Conversions
| ng/g | ppb |
|---|---|
| 0.1 | 0.1 |
| 1 | 1 |
| 5 | 5 |
| 10 | 10 |
| 50 | 50 |
| 100 | 100 |
| 500 | 500 |
| 1000 | 1000 |
| 5000 | 5000 |
| 10000 | 10000 |
| 100000 | 100000 |
| 1000000 | 1000000 |
Why this conversion matters in chemistry
For solid and tissue samples, ng/g and ppb describe the same mass ratio. Both are nanograms of analyte per 10⁹ ng of sample. A 25 ng/g PCB result on a fish-tissue composite is 25 ppb on a regulatory consumption advisory — same number, two unit conventions. The identity rests on the mass per mass framing; for liquid samples reported in ng/mL, the equivalence depends on density. Trace residue analysis runs almost entirely at this scale, which is why the two notations stay interchangeable in environmental and food-chemistry work.
Formula
Where the factor comes from
Divide nanograms by grams and the mass units cancel, leaving 10⁻⁹ — a pure number with no dimension left on it. Part per billion names that same pure number, on two conditions: that billion is read on the short scale as 10⁹, and that the ratio is taken by mass. Meet both and the factor is exactly one, an identity rather than a conversion, with nothing to measure and no constant to look up. The looseness lives in the destination unit rather than the arithmetic. ppb declares neither its basis nor its scale, so the same three letters carry a mole ratio in atmospheric work, a volume ratio in gas blending, and a mass ratio in a sediment report. Writing ng/g strips that ambiguity out, which is the argument for keeping the explicit form on the analytical record.
Precision and significant figures
Whatever the analysis earned is what the ppb figure is worth, since a factor of exactly one shifts no digits — usually two significant figures at this level, occasionally three. Weighing is not the constraint: a one gram aliquot on a four-place balance is good to a hundredth of a percent. Extraction recovery, matrix suppression in the source, and the business of subsampling a heterogeneous solid are the constraints, and they contribute anywhere from percent-level to tens of percent. Results within a few multiples of the quantitation limit deserve fewer digits still. A value reported as 0.8 ng/g should not reappear as 0.80 ppb after the relabel; crossing between notations improves nothing.
Worked Examples
The identity itself — one nanogram per gram is one part per 10⁹ by mass.
A trace contaminant at the low end of routine analytical detection in a solid matrix.
An elevated contaminant level — well above background for many regulated trace analytes in food or sediment.
Equivalently 1 ppm or 1 mg/kg — the boundary where the next prefix up becomes more readable.
Common mistakes
Non-detects lose their qualifier in the relabel
A result written as <0.5 ng/g is a limit, not a concentration. Because the step to ppb changes nothing numerically, the digits copy across cleanly while the less-than sign, the reporting limit it points at, and the flag saying the analyte was never seen are exactly the parts that fall off in transit. Carry the qualifier or carry nothing.
Extract concentration is not sample concentration
An instrument reading of 20 ng/mL on an extract says nothing directly about the solid it came from. Carry the volume and the mass through: 20 ng/mL in 10 mL of final extract is 200 ng, and out of a 5 g subsample that is 40 ng/g. Skipping the bookkeeping because both units already end in ng is a standard way to land off by the extraction ratio.
Billion means different things
Billion is 10⁹ in English-language scientific usage but 10¹² on the long scale that several continental European languages still keep — a factor of a thousand apart. That ambiguity is exactly why ppb draws criticism as a unit of record. When an archived result looks a thousandfold out of family, rule out the scale convention before rethinking the chemistry.