g/kg to PPM Converter
Common Conversions
| g/kg | ppm |
|---|---|
| 0.001 | 1 |
| 0.01 | 10 |
| 0.1 | 100 |
| 0.5 | 500 |
| 1 | 1000 |
| 2 | 2000 |
| 5 | 5000 |
| 10 | 10000 |
| 25 | 25000 |
| 50 | 50000 |
| 100 | 100000 |
| 1000 | 1000000 |
Why this conversion matters in chemistry
Brownfield-soil cleanup math sits on top of this conversion. A heavily contaminated former-smelter sample at 5 g/kg lead is 5000 ppm — orders of magnitude above any residential soil screening level. The same g/kg digestion result lands cleanly into the ppm scale the regulator's cleanup threshold is written in. 1000 ppm per g/kg follows from the definition: ppm is g per 10⁶ g, and g/kg is g per 10³ g, so the ratio is exactly 1000. The conversion is a unit step in any soil-contamination, food-analysis, or solid-matrix calculation that crosses between the two notations.
Formula
Where the factor comes from
Nothing in this pair involves a volume, and that is what keeps it exact. Both sides are mass fractions: g/kg is grams of analyte per kilogram of sample, and ppm on a mass basis is grams per million grams. The kilo prefix carries an exact decimal value, so 1 g/kg is 1 g per 10³ g, or 10⁻³ written as a bare fraction, while 1 ppm is 10⁻⁶. Divide one by the other and you get exactly 1000. The gram cancels on both sides, so no molar mass, no density and no solvent property ever enters the calculation. That is worth stating plainly, because ppm is not an SI unit and carries no basis of its own — mass, volume and mole bases all travel under the same three letters, and only the mass reading gives this clean factor.
Precision and significant figures
Because the factor is exact, the digit count survives untouched: 2.4 g/kg is 2400 ppm at two significant figures, not four. Everything that limits the result comes from the sample rather than the arithmetic. Solid matrices are heterogeneous, and for a coarse or poorly ground material the variance between two subsamples of the same lot routinely exceeds the combined uncertainty of the digestion and the instrument. Two significant figures, sometimes three, is what a trace result on a solid honestly supports. Writing 1 g/kg as 1000.00 ppm dresses up a homogenization step that was never that good.
Worked Examples
The conversion anchor — exactly one part per thousand.
1 mg/kg — the typical scale of residential soil-contamination screening work.
100 mg/kg — the same order as residential screening levels for lead.
Exactly 1% by weight — the boundary where ppm starts to feel cumbersome and percent takes over.
Common mistakes
ppm quoted without stating its basis
Mass, volume and mole bases all get written as ppm. Only the mass basis converts to g/kg by a factor of 1000; a gas-phase ppm is a mole fraction and bears no relation to this factor at all. When a result arrives as a bare 'ppm' with no denominator declared, chase down what it was divided by before converting anything.
Wet-weight and dry-weight results compared directly
Soil and food results are reported on either an as-received or an oven-dried basis, and the two differ by the moisture content alone. A sample holding 20% water gives a dry-basis figure 1.25 times the wet-basis one — a 25% shift with no analytical error involved. Converting g/kg to ppm does nothing about this; the bases have to match first.
Carrying the same 1000 into a liquid result
This pair is mass over mass from end to end. The moment the sample is a solution reported in g/L, the same 1000 stops being exact, because ppm by mass then needs the solution density to bridge volume to mass. The two conversions look identical written down and are not: one is definitional, the other rests on an assumption about density.